diff --git a/python/PyQt6/core/auto_additions/qgsgeometry.py b/python/PyQt6/core/auto_additions/qgsgeometry.py
index c8dc6afb58e6..60f8167f6915 100644
--- a/python/PyQt6/core/auto_additions/qgsgeometry.py
+++ b/python/PyQt6/core/auto_additions/qgsgeometry.py
@@ -12,6 +12,7 @@
     QgsGeometry.fromRect = staticmethod(QgsGeometry.fromRect)
     QgsGeometry.fromBox3D = staticmethod(QgsGeometry.fromBox3D)
     QgsGeometry.collectGeometry = staticmethod(QgsGeometry.collectGeometry)
+    QgsGeometry.collectTinPatches = staticmethod(QgsGeometry.collectTinPatches)
     QgsGeometry.createWedgeBuffer = staticmethod(QgsGeometry.createWedgeBuffer)
     QgsGeometry.createWedgeBufferFromAngles = staticmethod(QgsGeometry.createWedgeBufferFromAngles)
     QgsGeometry.unaryUnion = staticmethod(QgsGeometry.unaryUnion)
diff --git a/python/PyQt6/core/auto_generated/geometry/qgsgeometry.sip.in b/python/PyQt6/core/auto_generated/geometry/qgsgeometry.sip.in
index cfa76dfc0e9a..036dd9352c38 100644
--- a/python/PyQt6/core/auto_generated/geometry/qgsgeometry.sip.in
+++ b/python/PyQt6/core/auto_generated/geometry/qgsgeometry.sip.in
@@ -41,7 +41,6 @@ Encapsulates parameters under which a geometry operation is performed.
 #include "qgsgeometry.h"
 %End
   public:
-
     double gridSize() const;
 %Docstring
 Returns the grid size which will be used to snap vertices of a geometry.
@@ -105,7 +104,6 @@ as the point, line, polygon, curve or other geometry subclasses.
     static const QMetaObject staticMetaObject;
 
   public:
-
     QgsGeometry() /HoldGIL/;
 
     QgsGeometry( const QgsGeometry & );
@@ -290,8 +288,31 @@ surface geometry.
 Creates a new multipart geometry from a list of QgsGeometry objects
 %End
 
-    static QgsGeometry createWedgeBuffer( const QgsPoint &center, double azimuth, double angularWidth,
-                                          double outerRadius, double innerRadius = 0 );
+    static QgsGeometry collectTinPatches( const QVector<QgsGeometry> &geometries );
+%Docstring
+Collects all patches from a list of TIN or Triangle geometries into a
+single TIN geometry.
+
+This method iterates through the input ``geometries`` and extracts all
+triangle patches, combining them into a single
+:py:class:`QgsTriangulatedSurface`. Input geometries can be either
+:py:class:`QgsTriangulatedSurface` (TIN) or :py:class:`QgsTriangle`
+objects. Other geometry types are ignored.
+
+The resulting TIN will preserve Z and M values if present in the first
+valid input geometry.
+
+:param geometries: list of input geometries (should be TIN or Triangle
+                   types)
+
+:return: a QgsGeometry containing a QgsTriangulatedSurface with all
+         collected patches, or a null geometry if no valid TIN/Triangle
+         geometries were found
+
+.. versionadded:: 4.0
+%End
+
+    static QgsGeometry createWedgeBuffer( const QgsPoint &center, double azimuth, double angularWidth, double outerRadius, double innerRadius = 0 );
 %Docstring
 Creates a wedge shaped buffer from a ``center`` point.
 
@@ -310,8 +331,7 @@ Polygon geometry.
 .. versionadded:: 3.2
 %End
 
-    static QgsGeometry createWedgeBufferFromAngles( const QgsPoint &center, double startAngle, double endAngle,
-        double outerRadius, double innerRadius = 0 );
+    static QgsGeometry createWedgeBufferFromAngles( const QgsPoint &center, double startAngle, double endAngle, double outerRadius, double innerRadius = 0 );
 %Docstring
 Creates a wedge shaped buffer from a ``center`` point.
 
@@ -1111,8 +1131,7 @@ Example:
       if ( PyList_Check( a0 ) && PyList_GET_SIZE( a0 ) )
       {
         PyObject *p0 = PyList_GetItem( a0, 0 );
-        if ( sipCanConvertToType( p0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-             sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+        if ( sipCanConvertToType( p0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
         {
           QVector<QgsGeometry> newGeometries;
           QVector<QgsPointXY> topologyTestPoints;
@@ -1134,8 +1153,7 @@ Example:
           sipReleaseType( splitLine, sipType_QVector_0100QgsPointXY, state );
         }
 
-        else if ( sipCanConvertToType( p0, sipType_QgsPoint, SIP_NOT_NONE ) &&
-                  sipCanConvertToType( a0, sipType_QVector_0100QgsPoint, SIP_NOT_NONE ) )
+        else if ( sipCanConvertToType( p0, sipType_QgsPoint, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0100QgsPoint, SIP_NOT_NONE ) )
         {
           QVector<QgsGeometry> newGeometries;
           QVector<QgsPoint> topologyTestPoints;
@@ -1170,7 +1188,7 @@ Example:
     }
 %End
 
-    Qgis::GeometryOperationResult splitGeometry( const QgsCurve *curve,  QVector<QgsGeometry> &newGeometries /Out/, bool preserveCircular, bool topological, QgsPointSequence &topologyTestPoints /Out/, bool splitFeature = true );
+    Qgis::GeometryOperationResult splitGeometry( const QgsCurve *curve, QVector<QgsGeometry> &newGeometries /Out/, bool preserveCircular, bool topological, QgsPointSequence &topologyTestPoints /Out/, bool splitFeature = true );
 %Docstring
 Splits this geometry according to a given curve.
 
@@ -1391,11 +1409,7 @@ will be generated.
 .. versionadded:: 3.24
 %End
 
-    QgsGeometry applyDashPattern( const QVector< double > &pattern,
-                                  Qgis::DashPatternLineEndingRule startRule = Qgis::DashPatternLineEndingRule::NoRule,
-                                  Qgis::DashPatternLineEndingRule endRule = Qgis::DashPatternLineEndingRule::NoRule,
-                                  Qgis::DashPatternSizeAdjustment adjustment = Qgis::DashPatternSizeAdjustment::ScaleBothDashAndGap,
-                                  double patternOffset = 0 ) const;
+    QgsGeometry applyDashPattern( const QVector< double > &pattern, Qgis::DashPatternLineEndingRule startRule = Qgis::DashPatternLineEndingRule::NoRule, Qgis::DashPatternLineEndingRule endRule = Qgis::DashPatternLineEndingRule::NoRule, Qgis::DashPatternSizeAdjustment adjustment = Qgis::DashPatternSizeAdjustment::ScaleBothDashAndGap, double patternOffset = 0 ) const;
 %Docstring
 Applies a dash pattern to a geometry, returning a MultiLineString
 geometry which is the input geometry stroked along each line/ring with
@@ -1629,9 +1643,7 @@ Returns an offset line at a given distance and side from an input line.
                    (JoinStyleMiter only)
 %End
 
-    QgsGeometry singleSidedBuffer( double distance, int segments, Qgis::BufferSide side,
-                                   Qgis::JoinStyle joinStyle = Qgis::JoinStyle::Round,
-                                   double miterLimit = 2.0 ) const;
+    QgsGeometry singleSidedBuffer( double distance, int segments, Qgis::BufferSide side, Qgis::JoinStyle joinStyle = Qgis::JoinStyle::Round, double miterLimit = 2.0 ) const;
 %Docstring
 Returns a single sided buffer for a (multi)line geometry. The buffer is
 only applied to one side of the line.
@@ -2358,6 +2370,8 @@ the specified type. E.g.
 - curved geometries will be segmented if ``type`` is non-curved.
 - multi geometries will be converted to a list of single geometries
 - single geometries will be upgraded to multi geometries
+- PolyhedralSurface/TIN will be converted to multi polygon
+- multipolygon, polygon and triangle will be converted to TIN
 - z or m values will be added or dropped as required.
 
 Since QGIS 3.24, the parameters ``defaultZ`` and ``defaultM`` control
@@ -2375,6 +2389,12 @@ geometries to points. By default duplicated nodes are ignored.
    to coerce geometries to the desired ``type``. It also correctly maintains curves and z/m values
    wherever appropriate.
 
+.. note::
+
+   If an error occurs during conversion (e.g., attempting to convert a polygon with
+   non-triangular vertices to a Triangle or TIN geometry), an empty vector will be returned and the
+   error message can be retrieved by calling :py:func:`~QgsGeometry.lastError` on the returned geometry.
+
 .. versionadded:: 3.14
 %End
 
@@ -3093,18 +3113,14 @@ should match.
       int state1;
       int sipIsErr = 0;
 
-      if ( PyList_Check( a0 ) && PyList_Check( a1 ) &&
-           PyList_GET_SIZE( a0 ) && PyList_GET_SIZE( a1 ) )
+      if ( PyList_Check( a0 ) && PyList_Check( a1 ) && PyList_GET_SIZE( a0 ) && PyList_GET_SIZE( a1 ) )
       {
         PyObject *o0 = PyList_GetItem( a0, 0 );
         PyObject *o1 = PyList_GetItem( a1, 0 );
         if ( o0 && o1 )
         {
           // compare polyline - polyline
-          if ( sipCanConvertToType( o0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-               sipCanConvertToType( o1, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-               sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) &&
-               sipCanConvertToType( a1, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+          if ( sipCanConvertToType( o0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( o1, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a1, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
           {
             QgsPolylineXY *p0;
             QgsPolylineXY *p1;
@@ -3117,18 +3133,14 @@ should match.
             sipReleaseType( p0, sipType_QVector_0100QgsPointXY, state0 );
             sipReleaseType( p1, sipType_QVector_0100QgsPointXY, state1 );
           }
-          else if ( PyList_Check( o0 ) && PyList_Check( o1 ) &&
-                    PyList_GET_SIZE( o0 ) && PyList_GET_SIZE( o1 ) )
+          else if ( PyList_Check( o0 ) && PyList_Check( o1 ) && PyList_GET_SIZE( o0 ) && PyList_GET_SIZE( o1 ) )
           {
             PyObject *oo0 = PyList_GetItem( o0, 0 );
             PyObject *oo1 = PyList_GetItem( o1, 0 );
             if ( oo0 && oo1 )
             {
               // compare polygon - polygon
-              if ( sipCanConvertToType( oo0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                   sipCanConvertToType( oo1, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                   sipCanConvertToType( a0, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) &&
-                   sipCanConvertToType( a1, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+              if ( sipCanConvertToType( oo0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( oo1, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a1, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
               {
                 QgsPolygonXY *p0;
                 QgsPolygonXY *p1;
@@ -3141,18 +3153,14 @@ should match.
                 sipReleaseType( p0, sipType_QVector_0600QVector_0100QgsPointXY, state0 );
                 sipReleaseType( p1, sipType_QVector_0600QVector_0100QgsPointXY, state1 );
               }
-              else if ( PyList_Check( oo0 ) && PyList_Check( oo1 ) &&
-                        PyList_GET_SIZE( oo0 ) && PyList_GET_SIZE( oo1 ) )
+              else if ( PyList_Check( oo0 ) && PyList_Check( oo1 ) && PyList_GET_SIZE( oo0 ) && PyList_GET_SIZE( oo1 ) )
               {
                 PyObject *ooo0 = PyList_GetItem( oo0, 0 );
                 PyObject *ooo1 = PyList_GetItem( oo1, 0 );
                 if ( ooo0 && ooo1 )
                 {
                   // compare multipolygon - multipolygon
-                  if ( sipCanConvertToType( ooo0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                       sipCanConvertToType( ooo1, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                       sipCanConvertToType( a0, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) &&
-                       sipCanConvertToType( a1, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+                  if ( sipCanConvertToType( ooo0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( ooo1, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a1, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
                   {
                     QgsMultiPolygonXY *p0;
                     QgsMultiPolygonXY *p1;
@@ -3174,8 +3182,7 @@ should match.
     }
 %End
 
-    QgsGeometry smooth( unsigned int iterations = 1, double offset = 0.25,
-                        double minimumDistance = -1.0, double maxAngle = 180.0 ) const;
+    QgsGeometry smooth( unsigned int iterations = 1, double offset = 0.25, double minimumDistance = -1.0, double maxAngle = 180.0 ) const;
 %Docstring
 Smooths a geometry by rounding off corners using the Chaikin algorithm.
 This operation roughly doubles the number of vertices in a geometry.
diff --git a/python/core/auto_additions/qgsgeometry.py b/python/core/auto_additions/qgsgeometry.py
index c8dc6afb58e6..60f8167f6915 100644
--- a/python/core/auto_additions/qgsgeometry.py
+++ b/python/core/auto_additions/qgsgeometry.py
@@ -12,6 +12,7 @@
     QgsGeometry.fromRect = staticmethod(QgsGeometry.fromRect)
     QgsGeometry.fromBox3D = staticmethod(QgsGeometry.fromBox3D)
     QgsGeometry.collectGeometry = staticmethod(QgsGeometry.collectGeometry)
+    QgsGeometry.collectTinPatches = staticmethod(QgsGeometry.collectTinPatches)
     QgsGeometry.createWedgeBuffer = staticmethod(QgsGeometry.createWedgeBuffer)
     QgsGeometry.createWedgeBufferFromAngles = staticmethod(QgsGeometry.createWedgeBufferFromAngles)
     QgsGeometry.unaryUnion = staticmethod(QgsGeometry.unaryUnion)
diff --git a/python/core/auto_generated/geometry/qgsgeometry.sip.in b/python/core/auto_generated/geometry/qgsgeometry.sip.in
index f24e1079922a..ce323c5aa897 100644
--- a/python/core/auto_generated/geometry/qgsgeometry.sip.in
+++ b/python/core/auto_generated/geometry/qgsgeometry.sip.in
@@ -41,7 +41,6 @@ Encapsulates parameters under which a geometry operation is performed.
 #include "qgsgeometry.h"
 %End
   public:
-
     double gridSize() const;
 %Docstring
 Returns the grid size which will be used to snap vertices of a geometry.
@@ -105,7 +104,6 @@ as the point, line, polygon, curve or other geometry subclasses.
     static const QMetaObject staticMetaObject;
 
   public:
-
     QgsGeometry() /HoldGIL/;
 
     QgsGeometry( const QgsGeometry & );
@@ -290,8 +288,31 @@ surface geometry.
 Creates a new multipart geometry from a list of QgsGeometry objects
 %End
 
-    static QgsGeometry createWedgeBuffer( const QgsPoint &center, double azimuth, double angularWidth,
-                                          double outerRadius, double innerRadius = 0 );
+    static QgsGeometry collectTinPatches( const QVector<QgsGeometry> &geometries );
+%Docstring
+Collects all patches from a list of TIN or Triangle geometries into a
+single TIN geometry.
+
+This method iterates through the input ``geometries`` and extracts all
+triangle patches, combining them into a single
+:py:class:`QgsTriangulatedSurface`. Input geometries can be either
+:py:class:`QgsTriangulatedSurface` (TIN) or :py:class:`QgsTriangle`
+objects. Other geometry types are ignored.
+
+The resulting TIN will preserve Z and M values if present in the first
+valid input geometry.
+
+:param geometries: list of input geometries (should be TIN or Triangle
+                   types)
+
+:return: a QgsGeometry containing a QgsTriangulatedSurface with all
+         collected patches, or a null geometry if no valid TIN/Triangle
+         geometries were found
+
+.. versionadded:: 4.0
+%End
+
+    static QgsGeometry createWedgeBuffer( const QgsPoint &center, double azimuth, double angularWidth, double outerRadius, double innerRadius = 0 );
 %Docstring
 Creates a wedge shaped buffer from a ``center`` point.
 
@@ -310,8 +331,7 @@ Polygon geometry.
 .. versionadded:: 3.2
 %End
 
-    static QgsGeometry createWedgeBufferFromAngles( const QgsPoint &center, double startAngle, double endAngle,
-        double outerRadius, double innerRadius = 0 );
+    static QgsGeometry createWedgeBufferFromAngles( const QgsPoint &center, double startAngle, double endAngle, double outerRadius, double innerRadius = 0 );
 %Docstring
 Creates a wedge shaped buffer from a ``center`` point.
 
@@ -1111,8 +1131,7 @@ Example:
       if ( PyList_Check( a0 ) && PyList_GET_SIZE( a0 ) )
       {
         PyObject *p0 = PyList_GetItem( a0, 0 );
-        if ( sipCanConvertToType( p0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-             sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+        if ( sipCanConvertToType( p0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
         {
           QVector<QgsGeometry> newGeometries;
           QVector<QgsPointXY> topologyTestPoints;
@@ -1134,8 +1153,7 @@ Example:
           sipReleaseType( splitLine, sipType_QVector_0100QgsPointXY, state );
         }
 
-        else if ( sipCanConvertToType( p0, sipType_QgsPoint, SIP_NOT_NONE ) &&
-                  sipCanConvertToType( a0, sipType_QVector_0100QgsPoint, SIP_NOT_NONE ) )
+        else if ( sipCanConvertToType( p0, sipType_QgsPoint, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0100QgsPoint, SIP_NOT_NONE ) )
         {
           QVector<QgsGeometry> newGeometries;
           QVector<QgsPoint> topologyTestPoints;
@@ -1170,7 +1188,7 @@ Example:
     }
 %End
 
-    Qgis::GeometryOperationResult splitGeometry( const QgsCurve *curve,  QVector<QgsGeometry> &newGeometries /Out/, bool preserveCircular, bool topological, QgsPointSequence &topologyTestPoints /Out/, bool splitFeature = true );
+    Qgis::GeometryOperationResult splitGeometry( const QgsCurve *curve, QVector<QgsGeometry> &newGeometries /Out/, bool preserveCircular, bool topological, QgsPointSequence &topologyTestPoints /Out/, bool splitFeature = true );
 %Docstring
 Splits this geometry according to a given curve.
 
@@ -1391,11 +1409,7 @@ will be generated.
 .. versionadded:: 3.24
 %End
 
-    QgsGeometry applyDashPattern( const QVector< double > &pattern,
-                                  Qgis::DashPatternLineEndingRule startRule = Qgis::DashPatternLineEndingRule::NoRule,
-                                  Qgis::DashPatternLineEndingRule endRule = Qgis::DashPatternLineEndingRule::NoRule,
-                                  Qgis::DashPatternSizeAdjustment adjustment = Qgis::DashPatternSizeAdjustment::ScaleBothDashAndGap,
-                                  double patternOffset = 0 ) const;
+    QgsGeometry applyDashPattern( const QVector< double > &pattern, Qgis::DashPatternLineEndingRule startRule = Qgis::DashPatternLineEndingRule::NoRule, Qgis::DashPatternLineEndingRule endRule = Qgis::DashPatternLineEndingRule::NoRule, Qgis::DashPatternSizeAdjustment adjustment = Qgis::DashPatternSizeAdjustment::ScaleBothDashAndGap, double patternOffset = 0 ) const;
 %Docstring
 Applies a dash pattern to a geometry, returning a MultiLineString
 geometry which is the input geometry stroked along each line/ring with
@@ -1629,9 +1643,7 @@ Returns an offset line at a given distance and side from an input line.
                    (JoinStyleMiter only)
 %End
 
-    QgsGeometry singleSidedBuffer( double distance, int segments, Qgis::BufferSide side,
-                                   Qgis::JoinStyle joinStyle = Qgis::JoinStyle::Round,
-                                   double miterLimit = 2.0 ) const;
+    QgsGeometry singleSidedBuffer( double distance, int segments, Qgis::BufferSide side, Qgis::JoinStyle joinStyle = Qgis::JoinStyle::Round, double miterLimit = 2.0 ) const;
 %Docstring
 Returns a single sided buffer for a (multi)line geometry. The buffer is
 only applied to one side of the line.
@@ -2358,6 +2370,8 @@ the specified type. E.g.
 - curved geometries will be segmented if ``type`` is non-curved.
 - multi geometries will be converted to a list of single geometries
 - single geometries will be upgraded to multi geometries
+- PolyhedralSurface/TIN will be converted to multi polygon
+- multipolygon, polygon and triangle will be converted to TIN
 - z or m values will be added or dropped as required.
 
 Since QGIS 3.24, the parameters ``defaultZ`` and ``defaultM`` control
@@ -2375,6 +2389,12 @@ geometries to points. By default duplicated nodes are ignored.
    to coerce geometries to the desired ``type``. It also correctly maintains curves and z/m values
    wherever appropriate.
 
+.. note::
+
+   If an error occurs during conversion (e.g., attempting to convert a polygon with
+   non-triangular vertices to a Triangle or TIN geometry), an empty vector will be returned and the
+   error message can be retrieved by calling :py:func:`~QgsGeometry.lastError` on the returned geometry.
+
 .. versionadded:: 3.14
 %End
 
@@ -3093,18 +3113,14 @@ should match.
       int state1;
       int sipIsErr = 0;
 
-      if ( PyList_Check( a0 ) && PyList_Check( a1 ) &&
-           PyList_GET_SIZE( a0 ) && PyList_GET_SIZE( a1 ) )
+      if ( PyList_Check( a0 ) && PyList_Check( a1 ) && PyList_GET_SIZE( a0 ) && PyList_GET_SIZE( a1 ) )
       {
         PyObject *o0 = PyList_GetItem( a0, 0 );
         PyObject *o1 = PyList_GetItem( a1, 0 );
         if ( o0 && o1 )
         {
           // compare polyline - polyline
-          if ( sipCanConvertToType( o0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-               sipCanConvertToType( o1, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-               sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) &&
-               sipCanConvertToType( a1, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+          if ( sipCanConvertToType( o0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( o1, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a1, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
           {
             QgsPolylineXY *p0;
             QgsPolylineXY *p1;
@@ -3117,18 +3133,14 @@ should match.
             sipReleaseType( p0, sipType_QVector_0100QgsPointXY, state0 );
             sipReleaseType( p1, sipType_QVector_0100QgsPointXY, state1 );
           }
-          else if ( PyList_Check( o0 ) && PyList_Check( o1 ) &&
-                    PyList_GET_SIZE( o0 ) && PyList_GET_SIZE( o1 ) )
+          else if ( PyList_Check( o0 ) && PyList_Check( o1 ) && PyList_GET_SIZE( o0 ) && PyList_GET_SIZE( o1 ) )
           {
             PyObject *oo0 = PyList_GetItem( o0, 0 );
             PyObject *oo1 = PyList_GetItem( o1, 0 );
             if ( oo0 && oo1 )
             {
               // compare polygon - polygon
-              if ( sipCanConvertToType( oo0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                   sipCanConvertToType( oo1, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                   sipCanConvertToType( a0, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) &&
-                   sipCanConvertToType( a1, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+              if ( sipCanConvertToType( oo0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( oo1, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a1, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
               {
                 QgsPolygonXY *p0;
                 QgsPolygonXY *p1;
@@ -3141,18 +3153,14 @@ should match.
                 sipReleaseType( p0, sipType_QVector_0600QVector_0100QgsPointXY, state0 );
                 sipReleaseType( p1, sipType_QVector_0600QVector_0100QgsPointXY, state1 );
               }
-              else if ( PyList_Check( oo0 ) && PyList_Check( oo1 ) &&
-                        PyList_GET_SIZE( oo0 ) && PyList_GET_SIZE( oo1 ) )
+              else if ( PyList_Check( oo0 ) && PyList_Check( oo1 ) && PyList_GET_SIZE( oo0 ) && PyList_GET_SIZE( oo1 ) )
               {
                 PyObject *ooo0 = PyList_GetItem( oo0, 0 );
                 PyObject *ooo1 = PyList_GetItem( oo1, 0 );
                 if ( ooo0 && ooo1 )
                 {
                   // compare multipolygon - multipolygon
-                  if ( sipCanConvertToType( ooo0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                       sipCanConvertToType( ooo1, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                       sipCanConvertToType( a0, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) &&
-                       sipCanConvertToType( a1, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+                  if ( sipCanConvertToType( ooo0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( ooo1, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a1, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
                   {
                     QgsMultiPolygonXY *p0;
                     QgsMultiPolygonXY *p1;
@@ -3174,8 +3182,7 @@ should match.
     }
 %End
 
-    QgsGeometry smooth( unsigned int iterations = 1, double offset = 0.25,
-                        double minimumDistance = -1.0, double maxAngle = 180.0 ) const;
+    QgsGeometry smooth( unsigned int iterations = 1, double offset = 0.25, double minimumDistance = -1.0, double maxAngle = 180.0 ) const;
 %Docstring
 Smooths a geometry by rounding off corners using the Chaikin algorithm.
 This operation roughly doubles the number of vertices in a geometry.
diff --git a/src/app/qgisapp.cpp b/src/app/qgisapp.cpp
index 635b723efab7..e5c5166fafaa 100644
--- a/src/app/qgisapp.cpp
+++ b/src/app/qgisapp.cpp
@@ -93,6 +93,9 @@
 #include "qgsfixattributedialog.h"
 #include "qgsprojecttimesettings.h"
 #include "qgsgeometrycollection.h"
+#include "qgspolyhedralsurface.h"
+#include "qgstriangle.h"
+#include "qgstriangulatedsurface.h"
 #include "maptools/qgsappmaptools.h"
 #include "qgsexpressioncontextutils.h"
 #include "qgsauxiliarystorage.h"
@@ -8877,6 +8880,24 @@ QgsGeometry QgisApp::unionGeometries( const QgsVectorLayer *vl, QgsFeatureList &
   if ( !featureList.at( 0 ).hasGeometry() )
     return QgsGeometry();
 
+  const Qgis::WkbType layerFlatType = QgsWkbTypes::flatType( vl->wkbType() );
+
+  // Special handling for TIN: collect patches instead of geometric union
+  if ( layerFlatType == Qgis::WkbType::TIN )
+  {
+    QgsTemporaryCursorOverride waitCursor( Qt::WaitCursor );
+
+    QVector<QgsGeometry> geometries;
+    geometries.reserve( featureList.size() );
+    for ( const QgsFeature &feature : std::as_const( featureList ) )
+    {
+      geometries.append( feature.geometry() );
+    }
+
+    return QgsGeometry::collectTinPatches( geometries );
+  }
+
+  // Standard handling for other geometry types: use GEOS combine
   QgsGeometry unionGeom = featureList.at( 0 ).geometry();
 
   QProgressDialog progress( tr( "Merging features…" ), tr( "Abort" ), 0, featureList.size(), this );
@@ -8911,6 +8932,16 @@ QgsGeometry QgisApp::unionGeometries( const QgsVectorLayer *vl, QgsFeatureList &
     unionGeom.convertToMultiType();
   }
 
+  // Convert result to PolyhedralSurface if layer type requires it
+  if ( layerFlatType == Qgis::WkbType::PolyhedralSurface )
+  {
+    QVector<QgsGeometry> converted = unionGeom.coerceToType( vl->wkbType() );
+    if ( !converted.isEmpty() )
+    {
+      unionGeom = converted.at( 0 );
+    }
+  }
+
   QApplication::restoreOverrideCursor();
   progress.setValue( featureList.size() );
   return unionGeom;
diff --git a/src/app/qgsmaptooladdpart.cpp b/src/app/qgsmaptooladdpart.cpp
index 6637f1164660..2eb087faea48 100644
--- a/src/app/qgsmaptooladdpart.cpp
+++ b/src/app/qgsmaptooladdpart.cpp
@@ -211,10 +211,13 @@ QgsVectorLayer *QgsMapToolAddPart::getLayerAndCheckSelection()
   {
     // Only one selected feature
     // For single-type layers only allow features without geometry
+    // Exception: TIN and PolyhedralSurface can hold multiple patches even though they are "single" types
     QgsFeatureIterator selectedFeatures = layer->getSelectedFeatures();
     QgsFeature selectedFeature;
     selectedFeatures.nextFeature( selectedFeature );
-    if ( QgsWkbTypes::isSingleType( layer->wkbType() ) && selectedFeature.geometry().constGet() )
+    const Qgis::WkbType layerFlatType = QgsWkbTypes::flatType( layer->wkbType() );
+    const bool isSurfaceWithPatches = ( layerFlatType == Qgis::WkbType::TIN || layerFlatType == Qgis::WkbType::PolyhedralSurface );
+    if ( QgsWkbTypes::isSingleType( layer->wkbType() ) && !isSurfaceWithPatches && selectedFeature.geometry().constGet() )
     {
       selectionErrorMsg = tr( "This layer does not support multipart geometries." );
     }
diff --git a/src/core/geometry/qgsgeometry.cpp b/src/core/geometry/qgsgeometry.cpp
index f24f5074983a..483eac205b58 100644
--- a/src/core/geometry/qgsgeometry.cpp
+++ b/src/core/geometry/qgsgeometry.cpp
@@ -43,6 +43,7 @@ email                : morb at ozemail dot com dot au
 #include "qgspolyhedralsurface.h"
 #include "qgsrectangle.h"
 #include "qgstriangle.h"
+#include "qgstriangulatedsurface.h"
 #include "qgsvectorlayer.h"
 
 #include <QCache>
@@ -410,6 +411,61 @@ QgsGeometry QgsGeometry::collectGeometry( const QVector< QgsGeometry > &geometri
   return collected;
 }
 
+QgsGeometry QgsGeometry::collectTinPatches( const QVector<QgsGeometry> &geometries )
+{
+  auto resultTin = std::make_unique<QgsTriangulatedSurface>();
+  bool first = true;
+
+  for ( const QgsGeometry &geom : geometries )
+  {
+    if ( geom.isNull() )
+      continue;
+
+    const QgsAbstractGeometry *abstractGeom = geom.constGet();
+
+    if ( const QgsTriangulatedSurface *tin = qgsgeometry_cast<const QgsTriangulatedSurface *>( abstractGeom ) )
+    {
+      // Preserve Z/M from first valid geometry
+      if ( first )
+      {
+        if ( tin->is3D() )
+          resultTin->addZValue( 0 );
+        if ( tin->isMeasure() )
+          resultTin->addMValue( 0 );
+        first = false;
+      }
+
+      // Copy all patches (triangles) from the TIN
+      for ( int j = 0; j < tin->numPatches(); ++j )
+      {
+        if ( const QgsPolygon *patch = tin->patchN( j ) )
+        {
+          resultTin->addPatch( patch->clone() );
+        }
+      }
+    }
+    else if ( const QgsTriangle *triangle = qgsgeometry_cast<const QgsTriangle *>( abstractGeom ) )
+    {
+      // Preserve Z/M from first valid geometry
+      if ( first )
+      {
+        if ( triangle->is3D() )
+          resultTin->addZValue( 0 );
+        if ( triangle->isMeasure() )
+          resultTin->addMValue( 0 );
+        first = false;
+      }
+
+      resultTin->addPatch( triangle->clone() );
+    }
+  }
+
+  if ( resultTin->numPatches() == 0 )
+    return QgsGeometry();
+
+  return QgsGeometry( std::move( resultTin ) );
+}
+
 QgsGeometry QgsGeometry::createWedgeBuffer( const QgsPoint &center, const double azimuth, const double angularWidth, const double outerRadius, const double innerRadius )
 {
   const double startAngle = azimuth - angularWidth * 0.5;
@@ -1039,6 +1095,7 @@ Qgis::GeometryOperationResult QgsGeometry::addPartV2( QgsAbstractGeometry *part,
   std::unique_ptr< QgsAbstractGeometry > p( part );
   if ( !d->geometry )
   {
+    // NOLINTBEGIN(bugprone-branch-clone)
     switch ( QgsWkbTypes::singleType( QgsWkbTypes::flatType( wkbType ) ) )
     {
       case Qgis::WkbType::Point:
@@ -1058,15 +1115,27 @@ Qgis::GeometryOperationResult QgsGeometry::addPartV2( QgsAbstractGeometry *part,
       case Qgis::WkbType::CircularString:
         reset( std::make_unique< QgsMultiCurve >() );
         break;
+      case Qgis::WkbType::PolyhedralSurface:
+        reset( std::make_unique< QgsPolyhedralSurface >() );
+        break;
+      case Qgis::WkbType::TIN:
+        reset( std::make_unique< QgsTriangulatedSurface >() );
+        break;
       default:
         reset( nullptr );
         return Qgis::GeometryOperationResult::AddPartNotMultiGeometry;
+        // NOLINTEND(bugprone-branch-clone)
     }
   }
   else
   {
     detach();
-    convertToMultiType();
+    // For TIN and PolyhedralSurface, they already support multiple patches, no conversion needed
+    const Qgis::WkbType flatType = QgsWkbTypes::flatType( d->geometry->wkbType() );
+    if ( flatType != Qgis::WkbType::TIN && flatType != Qgis::WkbType::PolyhedralSurface )
+    {
+      convertToMultiType();
+    }
   }
 
   return QgsGeometryEditUtils::addPart( d->geometry.get(), std::move( p ) );
@@ -1719,6 +1788,7 @@ json QgsGeometry::asJsonObject( int precision ) const
 
 QVector<QgsGeometry> QgsGeometry::coerceToType( const Qgis::WkbType type, double defaultZ, double defaultM, bool avoidDuplicates ) const
 {
+  mLastError.clear();
   QVector< QgsGeometry > res;
   if ( isNull() )
     return res;
@@ -1814,17 +1884,82 @@ QVector<QgsGeometry> QgsGeometry::coerceToType( const Qgis::WkbType type, double
     newGeom = QgsGeometry( std::move( polySurface ) );
   }
 
+  //(Multi)Polygon/Triangle to TIN
+  if ( QgsWkbTypes::flatType( type ) == Qgis::WkbType::TIN &&
+       ( QgsWkbTypes::flatType( QgsWkbTypes::singleType( newGeom.wkbType() ) ) == Qgis::WkbType::Polygon ||
+         QgsWkbTypes::flatType( QgsWkbTypes::singleType( newGeom.wkbType() ) ) == Qgis::WkbType::Triangle ) )
+  {
+    auto tin = std::make_unique< QgsTriangulatedSurface >();
+    const QgsGeometry source = newGeom;
+    for ( auto part = source.const_parts_begin(); part != source.const_parts_end(); ++part )
+    {
+      if ( const QgsTriangle *triangle = qgsgeometry_cast< const QgsTriangle * >( *part ) )
+      {
+        tin->addPatch( triangle->clone() );
+      }
+      else if ( const QgsPolygon *polygon = qgsgeometry_cast< const QgsPolygon * >( *part ) )
+      {
+        // Validate that the polygon can be converted to a triangle (must have exactly 3 vertices + closing point)
+        if ( polygon->exteriorRing() )
+        {
+          const int numPoints = polygon->exteriorRing()->numPoints();
+          if ( numPoints != 4 )
+          {
+            mLastError = QObject::tr( "Cannot convert polygon with %1 vertices to a triangle. A triangle requires exactly 3 vertices." ).arg( numPoints > 0 ? numPoints - 1 : 0 );
+            return res;
+          }
+          auto triangle = std::make_unique< QgsTriangle >();
+          triangle->setExteriorRing( polygon->exteriorRing()->clone() );
+          tin->addPatch( triangle.release() );
+        }
+      }
+    }
+    newGeom = QgsGeometry( std::move( tin ) );
+  }
+
+  // PolyhedralSurface/TIN to (Multi)Polygon
+  if ( QgsWkbTypes::flatType( QgsWkbTypes::singleType( type ) ) == Qgis::WkbType::Polygon &&
+       ( QgsWkbTypes::flatType( newGeom.wkbType() ) == Qgis::WkbType::PolyhedralSurface ||
+         QgsWkbTypes::flatType( newGeom.wkbType() ) == Qgis::WkbType::TIN ) )
+  {
+    auto multiPolygon = std::make_unique< QgsMultiPolygon >();
+    if ( const QgsPolyhedralSurface *polySurface = qgsgeometry_cast< const QgsPolyhedralSurface * >( newGeom.constGet() ) )
+    {
+      for ( int i = 0; i < polySurface->numPatches(); ++i )
+      {
+        const QgsPolygon *patch = polySurface->patchN( i );
+        auto polygon = std::make_unique< QgsPolygon >();
+        polygon->setExteriorRing( patch->exteriorRing()->clone() );
+        for ( int j = 0; j < patch->numInteriorRings(); ++j )
+        {
+          polygon->addInteriorRing( patch->interiorRing( j )->clone() );
+        }
+        multiPolygon->addGeometry( polygon.release() );
+      }
+    }
+    newGeom = QgsGeometry( std::move( multiPolygon ) );
+  }
+
   // Polygon -> Triangle
   if ( QgsWkbTypes::flatType( type ) == Qgis::WkbType::Triangle &&
        QgsWkbTypes::flatType( newGeom.wkbType() ) == Qgis::WkbType::Polygon )
   {
-    auto triangle = std::make_unique< QgsTriangle >();
-    const QgsGeometry source = newGeom;
     if ( const QgsPolygon *polygon = qgsgeometry_cast< const QgsPolygon * >( newGeom.constGet() ) )
     {
-      triangle->setExteriorRing( polygon->exteriorRing()->clone() );
+      // Validate that the polygon can be converted to a triangle (must have exactly 3 vertices + closing point)
+      if ( polygon->exteriorRing() )
+      {
+        const int numPoints = polygon->exteriorRing()->numPoints();
+        if ( numPoints != 4 )
+        {
+          mLastError = QObject::tr( "Cannot convert polygon with %1 vertices to a triangle. A triangle requires exactly 3 vertices." ).arg( numPoints > 0 ? numPoints - 1 : 0 );
+          return res;
+        }
+        auto triangle = std::make_unique< QgsTriangle >();
+        triangle->setExteriorRing( polygon->exteriorRing()->clone() );
+        newGeom = QgsGeometry( std::move( triangle ) );
+      }
     }
-    newGeom = QgsGeometry( std::move( triangle ) );
   }
 
 
@@ -3786,6 +3921,27 @@ static bool vertexIndexInfo( const QgsAbstractGeometry *g, int vertexIndex, int
       partIndex++;
     }
   }
+  else if ( const QgsPolyhedralSurface *polySurface = qgsgeometry_cast<const QgsPolyhedralSurface *>( g ) )
+  {
+    // PolyhedralSurface: patches are the parts
+    partIndex = 0;
+    for ( int i = 0; i < polySurface->numPatches(); ++i )
+    {
+      const QgsPolygon *patch = polySurface->patchN( i );
+      // count total number of vertices in the patch
+      int numPoints = 0;
+      for ( int k = 0; k < patch->ringCount(); ++k )
+        numPoints += patch->vertexCount( 0, k );
+
+      if ( vertexIndex < numPoints )
+      {
+        int nothing;
+        return vertexIndexInfo( patch, vertexIndex, nothing, ringIndex, vertex );
+      }
+      vertexIndex -= numPoints;
+      partIndex++;
+    }
+  }
   else if ( const QgsCurvePolygon *curvePolygon = qgsgeometry_cast<const QgsCurvePolygon *>( g ) )
   {
     const QgsCurve *ring = curvePolygon->exteriorRing();
@@ -3854,6 +4010,10 @@ bool QgsGeometry::vertexIdFromVertexNr( int nr, QgsVertexId &id ) const
   {
     g = geomCollection->geometryN( id.part );
   }
+  else if ( const QgsPolyhedralSurface *polySurface = qgsgeometry_cast<const QgsPolyhedralSurface *>( g ) )
+  {
+    g = polySurface->patchN( id.part );
+  }
 
   if ( const QgsCurvePolygon *curvePolygon = qgsgeometry_cast<const QgsCurvePolygon *>( g ) )
   {
diff --git a/src/core/geometry/qgsgeometry.h b/src/core/geometry/qgsgeometry.h
index a773128add36..d3adbbe67840 100644
--- a/src/core/geometry/qgsgeometry.h
+++ b/src/core/geometry/qgsgeometry.h
@@ -124,7 +124,6 @@ struct QgsGeometryPrivate;
 class CORE_EXPORT QgsGeometryParameters
 {
   public:
-
     /**
      * Returns the grid size which will be used to snap vertices of a geometry.
      *
@@ -150,7 +149,6 @@ class CORE_EXPORT QgsGeometryParameters
     void setGridSize( double size ) { mGridSize = size; }
 
   private:
-
     double mGridSize = -1;
 };
 
@@ -181,7 +179,6 @@ class CORE_EXPORT QgsGeometry
     Q_PROPERTY( Qgis::GeometryType type READ type )
 
   public:
-
     QgsGeometry() SIP_HOLDGIL;
 
     //! Copy constructor will prompt a shallow copy of the geometry
@@ -345,6 +342,23 @@ class CORE_EXPORT QgsGeometry
     //! Creates a new multipart geometry from a list of QgsGeometry objects
     static QgsGeometry collectGeometry( const QVector<QgsGeometry> &geometries );
 
+    /**
+     * Collects all patches from a list of TIN or Triangle geometries into a single TIN geometry.
+     *
+     * This method iterates through the input \a geometries and extracts all triangle patches,
+     * combining them into a single QgsTriangulatedSurface. Input geometries can be either
+     * QgsTriangulatedSurface (TIN) or QgsTriangle objects. Other geometry types are ignored.
+     *
+     * The resulting TIN will preserve Z and M values if present in the first valid input geometry.
+     *
+     * \param geometries list of input geometries (should be TIN or Triangle types)
+     * \returns a QgsGeometry containing a QgsTriangulatedSurface with all collected patches,
+     *          or a null geometry if no valid TIN/Triangle geometries were found
+     *
+     * \since QGIS 4.0
+     */
+    static QgsGeometry collectTinPatches( const QVector<QgsGeometry> &geometries );
+
     /**
      * Creates a wedge shaped buffer from a \a center point.
      *
@@ -360,8 +374,7 @@ class CORE_EXPORT QgsGeometry
      *
      * \since QGIS 3.2
      */
-    static QgsGeometry createWedgeBuffer( const QgsPoint &center, double azimuth, double angularWidth,
-                                          double outerRadius, double innerRadius = 0 );
+    static QgsGeometry createWedgeBuffer( const QgsPoint &center, double azimuth, double angularWidth, double outerRadius, double innerRadius = 0 );
 
     /**
      * Creates a wedge shaped buffer from a \a center point.
@@ -376,8 +389,7 @@ class CORE_EXPORT QgsGeometry
      *
      * \since QGIS 3.40
      */
-    static QgsGeometry createWedgeBufferFromAngles( const QgsPoint &center, double startAngle, double endAngle,
-        double outerRadius, double innerRadius = 0 );
+    static QgsGeometry createWedgeBufferFromAngles( const QgsPoint &center, double startAngle, double endAngle, double outerRadius, double innerRadius = 0 );
 
     /**
      * Set the geometry, feeding in the buffer containing OGC Well-Known Binary and the buffer's length.
@@ -1131,8 +1143,7 @@ class CORE_EXPORT QgsGeometry
       if ( PyList_Check( a0 ) && PyList_GET_SIZE( a0 ) )
       {
         PyObject *p0 = PyList_GetItem( a0, 0 );
-        if ( sipCanConvertToType( p0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-             sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+        if ( sipCanConvertToType( p0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
         {
           QVector<QgsGeometry> newGeometries;
           QVector<QgsPointXY> topologyTestPoints;
@@ -1154,8 +1165,7 @@ class CORE_EXPORT QgsGeometry
           sipReleaseType( splitLine, sipType_QVector_0100QgsPointXY, state );
         }
 
-        else if ( sipCanConvertToType( p0, sipType_QgsPoint, SIP_NOT_NONE ) &&
-                  sipCanConvertToType( a0, sipType_QVector_0100QgsPoint, SIP_NOT_NONE ) )
+        else if ( sipCanConvertToType( p0, sipType_QgsPoint, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0100QgsPoint, SIP_NOT_NONE ) )
         {
           QVector<QgsGeometry> newGeometries;
           QVector<QgsPoint> topologyTestPoints;
@@ -1192,17 +1202,17 @@ class CORE_EXPORT QgsGeometry
 #endif
 
     /**
-     * Splits this geometry according to a given curve.
-     * \param curve the curve that splits the geometry
-     * \param[out] newGeometries list of new geometries that have been created with the ``splitLine``. If the geometry is 3D, a linear interpolation of the z value is performed on the geometry at split points, see example.
-     * \param preserveCircular whether if circular strings are preserved after splitting
-     * \param topological TRUE if topological editing is enabled
-     * \param[out] topologyTestPoints points that need to be tested for topological completeness in the dataset
-     * \param splitFeature Set to TRUE if you want to split a feature, otherwise set to FALSE to split parts
-     * \returns OperationResult a result code: success or reason of failure
-     * \since QGIS 3.16
-     */
-    Qgis::GeometryOperationResult splitGeometry( const QgsCurve *curve,  QVector<QgsGeometry> &newGeometries SIP_OUT, bool preserveCircular, bool topological, QgsPointSequence &topologyTestPoints SIP_OUT, bool splitFeature = true );
+    * Splits this geometry according to a given curve.
+    * \param curve the curve that splits the geometry
+    * \param[out] newGeometries list of new geometries that have been created with the ``splitLine``. If the geometry is 3D, a linear interpolation of the z value is performed on the geometry at split points, see example.
+    * \param preserveCircular whether if circular strings are preserved after splitting
+    * \param topological TRUE if topological editing is enabled
+    * \param[out] topologyTestPoints points that need to be tested for topological completeness in the dataset
+    * \param splitFeature Set to TRUE if you want to split a feature, otherwise set to FALSE to split parts
+    * \returns OperationResult a result code: success or reason of failure
+    * \since QGIS 3.16
+    */
+    Qgis::GeometryOperationResult splitGeometry( const QgsCurve *curve, QVector<QgsGeometry> &newGeometries SIP_OUT, bool preserveCircular, bool topological, QgsPointSequence &topologyTestPoints SIP_OUT, bool splitFeature = true );
 
     /**
      * Replaces a part of this geometry with another line
@@ -1402,11 +1412,7 @@ class CORE_EXPORT QgsGeometry
      *
      * \since QGIS 3.24
      */
-    QgsGeometry applyDashPattern( const QVector< double > &pattern,
-                                  Qgis::DashPatternLineEndingRule startRule = Qgis::DashPatternLineEndingRule::NoRule,
-                                  Qgis::DashPatternLineEndingRule endRule = Qgis::DashPatternLineEndingRule::NoRule,
-                                  Qgis::DashPatternSizeAdjustment adjustment = Qgis::DashPatternSizeAdjustment::ScaleBothDashAndGap,
-                                  double patternOffset = 0 ) const;
+    QgsGeometry applyDashPattern( const QVector< double > &pattern, Qgis::DashPatternLineEndingRule startRule = Qgis::DashPatternLineEndingRule::NoRule, Qgis::DashPatternLineEndingRule endRule = Qgis::DashPatternLineEndingRule::NoRule, Qgis::DashPatternSizeAdjustment adjustment = Qgis::DashPatternSizeAdjustment::ScaleBothDashAndGap, double patternOffset = 0 ) const;
 
     /**
      * Returns a new geometry with all points or vertices snapped to the closest point of the grid.
@@ -1612,9 +1618,7 @@ class CORE_EXPORT QgsGeometry
      * \see buffer()
      * \see taperedBuffer()
      */
-    QgsGeometry singleSidedBuffer( double distance, int segments, Qgis::BufferSide side,
-                                   Qgis::JoinStyle joinStyle = Qgis::JoinStyle::Round,
-                                   double miterLimit = 2.0 ) const;
+    QgsGeometry singleSidedBuffer( double distance, int segments, Qgis::BufferSide side, Qgis::JoinStyle joinStyle = Qgis::JoinStyle::Round, double miterLimit = 2.0 ) const;
 
     /**
      * Calculates a variable width buffer ("tapered buffer") for a (multi)curve geometry.
@@ -2188,7 +2192,7 @@ class CORE_EXPORT QgsGeometry
 
 
 #endif
-///@endcond
+    ///@endcond
 
     /**
      * Returns the length of the QByteArray returned by asWkb()
@@ -2232,8 +2236,8 @@ class CORE_EXPORT QgsGeometry
 #endif
 
     /**
-     * Exports the geometry to a GeoJSON string.
-     */
+    * Exports the geometry to a GeoJSON string.
+    */
     QString asJson( int precision = 17 ) const;
 
     /**
@@ -2256,6 +2260,8 @@ class CORE_EXPORT QgsGeometry
      * - curved geometries will be segmented if \a type is non-curved.
      * - multi geometries will be converted to a list of single geometries
      * - single geometries will be upgraded to multi geometries
+     * - PolyhedralSurface/TIN will be converted to  multi polygon
+     * - multipolygon, polygon and triangle will be converted to TIN
      * - z or m values will be added or dropped as required.
      *
      * Since QGIS 3.24, the parameters \a defaultZ and \a defaultM control the dimension value added when promoting geometries
@@ -2271,6 +2277,10 @@ class CORE_EXPORT QgsGeometry
      * to coerce geometries to the desired \a type. It also correctly maintains curves and z/m values
      * wherever appropriate.
      *
+     * \note If an error occurs during conversion (e.g., attempting to convert a polygon with
+     * non-triangular vertices to a Triangle or TIN geometry), an empty vector will be returned and the
+     * error message can be retrieved by calling lastError() on the returned geometry.
+     *
      * \since QGIS 3.14
      */
     QVector< QgsGeometry > coerceToType( Qgis::WkbType type, double defaultZ = 0, double defaultM = 0, bool avoidDuplicates = true ) const;
@@ -2350,16 +2360,16 @@ class CORE_EXPORT QgsGeometry
 #else
 
     /**
-     * Returns the contents of the geometry as a polyline.
-     *
-     * Any z or m values present in the geometry will be discarded. If the geometry is a curved line type
-     * (such as a CircularString), it will be automatically segmentized.
-     *
-     * This method works only with single-line (or single-curve).
-     *
-     * \throws TypeError if the geometry is not a single-line type
-     * \throws ValueError if the geometry is null
-     */
+    * Returns the contents of the geometry as a polyline.
+    *
+    * Any z or m values present in the geometry will be discarded. If the geometry is a curved line type
+    * (such as a CircularString), it will be automatically segmentized.
+    *
+    * This method works only with single-line (or single-curve).
+    *
+    * \throws TypeError if the geometry is not a single-line type
+    * \throws ValueError if the geometry is null
+    */
     SIP_PYOBJECT asPolyline() const SIP_TYPEHINT( QgsPolylineXY );
     % MethodCode
     const Qgis::WkbType type = sipCpp->wkbType();
@@ -2395,16 +2405,16 @@ class CORE_EXPORT QgsGeometry
 #else
 
     /**
-     * Returns the contents of the geometry as a polygon.
-     *
-     * Any z or m values present in the geometry will be discarded. If the geometry is a curved polygon type
-     * (such as a CurvePolygon), it will be automatically segmentized.
-     *
-     * This method works only with single-polygon (or single-curve polygon) geometry types.
-     *
-     * \throws TypeError if the geometry is not a single-polygon type
-     * \throws ValueError if the geometry is null
-     */
+    * Returns the contents of the geometry as a polygon.
+    *
+    * Any z or m values present in the geometry will be discarded. If the geometry is a curved polygon type
+    * (such as a CurvePolygon), it will be automatically segmentized.
+    *
+    * This method works only with single-polygon (or single-curve polygon) geometry types.
+    *
+    * \throws TypeError if the geometry is not a single-polygon type
+    * \throws ValueError if the geometry is null
+    */
     SIP_PYOBJECT asPolygon() const SIP_TYPEHINT( QgsPolygonXY );
     % MethodCode
     const Qgis::WkbType type = sipCpp->wkbType();
@@ -2439,15 +2449,15 @@ class CORE_EXPORT QgsGeometry
 #else
 
     /**
-     * Returns the contents of the geometry as a multi-point.
-     *
-     * Any z or m values present in the geometry will be discarded.
-     *
-     * This method works only with multi-point geometry types.
-     *
-     * \throws TypeError if the geometry is not a multi-point type
-     * \throws ValueError if the geometry is null
-     */
+    * Returns the contents of the geometry as a multi-point.
+    *
+    * Any z or m values present in the geometry will be discarded.
+    *
+    * This method works only with multi-point geometry types.
+    *
+    * \throws TypeError if the geometry is not a multi-point type
+    * \throws ValueError if the geometry is null
+    */
     SIP_PYOBJECT asMultiPoint() const SIP_TYPEHINT( QgsMultiPointXY );
     % MethodCode
     const Qgis::WkbType type = sipCpp->wkbType();
@@ -2483,16 +2493,16 @@ class CORE_EXPORT QgsGeometry
 #else
 
     /**
-     * Returns the contents of the geometry as a multi-linestring.
-     *
-     * Any z or m values present in the geometry will be discarded. If the geometry is a curved line type
-     * (such as a MultiCurve), it will be automatically segmentized.
-     *
-     * This method works only with multi-linestring (or multi-curve) geometry types.
-     *
-     * \throws TypeError if the geometry is not a multi-linestring type
-     * \throws ValueError if the geometry is null
-     */
+    * Returns the contents of the geometry as a multi-linestring.
+    *
+    * Any z or m values present in the geometry will be discarded. If the geometry is a curved line type
+    * (such as a MultiCurve), it will be automatically segmentized.
+    *
+    * This method works only with multi-linestring (or multi-curve) geometry types.
+    *
+    * \throws TypeError if the geometry is not a multi-linestring type
+    * \throws ValueError if the geometry is null
+    */
     SIP_PYOBJECT asMultiPolyline() const SIP_TYPEHINT( QgsMultiPolylineXY );
     % MethodCode
     const Qgis::WkbType type = sipCpp->wkbType();
@@ -2528,16 +2538,16 @@ class CORE_EXPORT QgsGeometry
 #else
 
     /**
-     * Returns the contents of the geometry as a multi-polygon.
-     *
-     * Any z or m values present in the geometry will be discarded. If the geometry is a curved polygon type
-     * (such as a MultiSurface), it will be automatically segmentized.
-     *
-     * This method works only with multi-polygon (or multi-curve polygon) geometry types.
-     *
-     * \throws TypeError if the geometry is not a multi-polygon type
-     * \throws ValueError if the geometry is null
-     */
+    * Returns the contents of the geometry as a multi-polygon.
+    *
+    * Any z or m values present in the geometry will be discarded. If the geometry is a curved polygon type
+    * (such as a MultiSurface), it will be automatically segmentized.
+    *
+    * This method works only with multi-polygon (or multi-curve polygon) geometry types.
+    *
+    * \throws TypeError if the geometry is not a multi-polygon type
+    * \throws ValueError if the geometry is null
+    */
     SIP_PYOBJECT asMultiPolygon() const SIP_TYPEHINT( QgsMultiPolygonXY );
     % MethodCode
     const Qgis::WkbType type = sipCpp->wkbType();
@@ -2656,8 +2666,7 @@ class CORE_EXPORT QgsGeometry
      *          4 if the geometry is not intersected by one of the geometries present in the provided layers.
      * \deprecated QGIS 3.34
      */
-    Q_DECL_DEPRECATED int avoidIntersections( const QList<QgsVectorLayer *> &avoidIntersectionsLayers,
-        const QHash<QgsVectorLayer *, QSet<QgsFeatureId> > &ignoreFeatures SIP_PYARGREMOVE = ( QHash<QgsVectorLayer *, QSet<QgsFeatureId> >() ) ) SIP_DEPRECATED;
+    Q_DECL_DEPRECATED int avoidIntersections( const QList<QgsVectorLayer *> &avoidIntersectionsLayers, const QHash<QgsVectorLayer *, QSet<QgsFeatureId> > &ignoreFeatures SIP_PYARGREMOVE = ( QHash<QgsVectorLayer *, QSet<QgsFeatureId> >() ) ) SIP_DEPRECATED;
 
     /**
      * Modifies geometry to avoid intersections with the layers specified in project properties
@@ -2670,8 +2679,7 @@ class CORE_EXPORT QgsGeometry
      *          NothingHappened          if the geometry is not intersected by one of the geometries present in the provided layers.
      * \since QGIS 3.34
      */
-    Qgis::GeometryOperationResult avoidIntersectionsV2( const QList<QgsVectorLayer *> &avoidIntersectionsLayers,
-        const QHash<QgsVectorLayer *, QSet<QgsFeatureId> > &ignoreFeatures SIP_PYARGREMOVE = ( QHash<QgsVectorLayer *, QSet<QgsFeatureId> >() ) );
+    Qgis::GeometryOperationResult avoidIntersectionsV2( const QList<QgsVectorLayer *> &avoidIntersectionsLayers, const QHash<QgsVectorLayer *, QSet<QgsFeatureId> > &ignoreFeatures SIP_PYARGREMOVE = ( QHash<QgsVectorLayer *, QSet<QgsFeatureId> >() ) );
 
     /**
      * Attempts to make an invalid geometry valid without losing vertices.
@@ -2998,8 +3006,7 @@ class CORE_EXPORT QgsGeometry
      * \returns TRUE if polylines have the same number of points and all
      * points are equal within the specified tolerance
      */
-    static bool compare( const QgsPolylineXY &p1, const QgsPolylineXY &p2,
-                         double epsilon = 4 * std::numeric_limits<double>::epsilon() );
+    static bool compare( const QgsPolylineXY &p1, const QgsPolylineXY &p2, double epsilon = 4 * std::numeric_limits<double>::epsilon() );
 
     /**
      * Compares two polygons for equality within a specified tolerance.
@@ -3009,8 +3016,7 @@ class CORE_EXPORT QgsGeometry
      * \returns TRUE if polygons have the same number of rings, and each ring has the same
      * number of points and all points are equal within the specified tolerance
      */
-    static bool compare( const QgsPolygonXY &p1, const QgsPolygonXY &p2,
-                         double epsilon = 4 * std::numeric_limits<double>::epsilon() );
+    static bool compare( const QgsPolygonXY &p1, const QgsPolygonXY &p2, double epsilon = 4 * std::numeric_limits<double>::epsilon() );
 
     /**
      * Compares two multipolygons for equality within a specified tolerance.
@@ -3021,8 +3027,7 @@ class CORE_EXPORT QgsGeometry
      * of rings, and each ring has the same number of points and all points are equal within the specified
      * tolerance
      */
-    static bool compare( const QgsMultiPolygonXY &p1, const QgsMultiPolygonXY &p2,
-                         double epsilon = 4 * std::numeric_limits<double>::epsilon() );
+    static bool compare( const QgsMultiPolygonXY &p1, const QgsMultiPolygonXY &p2, double epsilon = 4 * std::numeric_limits<double>::epsilon() );
 #else
 
     /**
@@ -3051,18 +3056,14 @@ class CORE_EXPORT QgsGeometry
       int state1;
       int sipIsErr = 0;
 
-      if ( PyList_Check( a0 ) && PyList_Check( a1 ) &&
-           PyList_GET_SIZE( a0 ) && PyList_GET_SIZE( a1 ) )
+      if ( PyList_Check( a0 ) && PyList_Check( a1 ) && PyList_GET_SIZE( a0 ) && PyList_GET_SIZE( a1 ) )
       {
         PyObject *o0 = PyList_GetItem( a0, 0 );
         PyObject *o1 = PyList_GetItem( a1, 0 );
         if ( o0 && o1 )
         {
           // compare polyline - polyline
-          if ( sipCanConvertToType( o0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-               sipCanConvertToType( o1, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-               sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) &&
-               sipCanConvertToType( a1, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+          if ( sipCanConvertToType( o0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( o1, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a1, sipType_QVector_0100QgsPointXY, SIP_NOT_NONE ) )
           {
             QgsPolylineXY *p0;
             QgsPolylineXY *p1;
@@ -3075,18 +3076,14 @@ class CORE_EXPORT QgsGeometry
             sipReleaseType( p0, sipType_QVector_0100QgsPointXY, state0 );
             sipReleaseType( p1, sipType_QVector_0100QgsPointXY, state1 );
           }
-          else if ( PyList_Check( o0 ) && PyList_Check( o1 ) &&
-                    PyList_GET_SIZE( o0 ) && PyList_GET_SIZE( o1 ) )
+          else if ( PyList_Check( o0 ) && PyList_Check( o1 ) && PyList_GET_SIZE( o0 ) && PyList_GET_SIZE( o1 ) )
           {
             PyObject *oo0 = PyList_GetItem( o0, 0 );
             PyObject *oo1 = PyList_GetItem( o1, 0 );
             if ( oo0 && oo1 )
             {
               // compare polygon - polygon
-              if ( sipCanConvertToType( oo0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                   sipCanConvertToType( oo1, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                   sipCanConvertToType( a0, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) &&
-                   sipCanConvertToType( a1, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+              if ( sipCanConvertToType( oo0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( oo1, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a1, sipType_QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
               {
                 QgsPolygonXY *p0;
                 QgsPolygonXY *p1;
@@ -3099,18 +3096,14 @@ class CORE_EXPORT QgsGeometry
                 sipReleaseType( p0, sipType_QVector_0600QVector_0100QgsPointXY, state0 );
                 sipReleaseType( p1, sipType_QVector_0600QVector_0100QgsPointXY, state1 );
               }
-              else if ( PyList_Check( oo0 ) && PyList_Check( oo1 ) &&
-                        PyList_GET_SIZE( oo0 ) && PyList_GET_SIZE( oo1 ) )
+              else if ( PyList_Check( oo0 ) && PyList_Check( oo1 ) && PyList_GET_SIZE( oo0 ) && PyList_GET_SIZE( oo1 ) )
               {
                 PyObject *ooo0 = PyList_GetItem( oo0, 0 );
                 PyObject *ooo1 = PyList_GetItem( oo1, 0 );
                 if ( ooo0 && ooo1 )
                 {
                   // compare multipolygon - multipolygon
-                  if ( sipCanConvertToType( ooo0, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                       sipCanConvertToType( ooo1, sipType_QgsPointXY, SIP_NOT_NONE ) &&
-                       sipCanConvertToType( a0, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) &&
-                       sipCanConvertToType( a1, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
+                  if ( sipCanConvertToType( ooo0, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( ooo1, sipType_QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a0, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) && sipCanConvertToType( a1, sipType_QVector_0600QVector_0600QVector_0100QgsPointXY, SIP_NOT_NONE ) )
                   {
                     QgsMultiPolygonXY *p0;
                     QgsMultiPolygonXY *p1;
@@ -3148,8 +3141,7 @@ class CORE_EXPORT QgsGeometry
      * \param minimumDistance minimum segment length to apply smoothing to
      * \param maxAngle maximum angle at node (0-180) at which smoothing will be applied
      */
-    QgsGeometry smooth( unsigned int iterations = 1, double offset = 0.25,
-                        double minimumDistance = -1.0, double maxAngle = 180.0 ) const;
+    QgsGeometry smooth( unsigned int iterations = 1, double offset = 0.25, double minimumDistance = -1.0, double maxAngle = 180.0 ) const;
 
     /**
      * Creates and returns a new geometry engine representing the specified \a geometry using \a precision on a grid. The \a precision argument was added in 3.36.
@@ -3300,7 +3292,6 @@ class CORE_EXPORT QgsGeometry
 
 
   private:
-
     QgsGeometryPrivate *d; //implicitly shared data pointer
 
     //! Last error encountered
@@ -3338,8 +3329,7 @@ class CORE_EXPORT QgsGeometry
      * \param minimumDistance minimum segment length to apply smoothing to
      * \param maxAngle maximum angle at node (0-180) at which smoothing will be applied
     */
-    std::unique_ptr< QgsLineString > smoothLine( const QgsLineString &line, unsigned int iterations = 1, double offset = 0.25,
-        double minimumDistance = -1, double maxAngle = 180.0 ) const;
+    std::unique_ptr< QgsLineString > smoothLine( const QgsLineString &line, unsigned int iterations = 1, double offset = 0.25, double minimumDistance = -1, double maxAngle = 180.0 ) const;
 
     /**
      * Smooths a polygon using the Chaikin algorithm
@@ -3352,8 +3342,7 @@ class CORE_EXPORT QgsGeometry
      * \param minimumDistance minimum segment length to apply smoothing to
      * \param maxAngle maximum angle at node (0-180) at which smoothing will be applied
     */
-    std::unique_ptr< QgsPolygon > smoothPolygon( const QgsPolygon &polygon, unsigned int iterations = 1, double offset = 0.25,
-        double minimumDistance = -1, double maxAngle = 180.0 ) const;
+    std::unique_ptr< QgsPolygon > smoothPolygon( const QgsPolygon &polygon, unsigned int iterations = 1, double offset = 0.25, double minimumDistance = -1, double maxAngle = 180.0 ) const;
 
     QgsGeometry doChamferFillet( ChamferFilletOperationType op, int vertexIndex, double distance1, double distance2, int segments ) const;
 
diff --git a/src/core/geometry/qgsgeometryeditutils.cpp b/src/core/geometry/qgsgeometryeditutils.cpp
index 6e56b2c9d5d2..6f429fc89aff 100644
--- a/src/core/geometry/qgsgeometryeditutils.cpp
+++ b/src/core/geometry/qgsgeometryeditutils.cpp
@@ -24,6 +24,9 @@ email                : marco.hugentobler at sourcepole dot com
 #include "qgsgeometrycollection.h"
 #include "qgsgeometryengine.h"
 #include "qgspolygon.h"
+#include "qgspolyhedralsurface.h"
+#include "qgstriangle.h"
+#include "qgstriangulatedsurface.h"
 #include "qgsvectorlayer.h"
 
 Qgis::GeometryOperationResult QgsGeometryEditUtils::addRing( QgsAbstractGeometry *geom, std::unique_ptr<QgsCurve> ring )
@@ -36,10 +39,21 @@ Qgis::GeometryOperationResult QgsGeometryEditUtils::addRing( QgsAbstractGeometry
   QVector< QgsCurvePolygon * > polygonList;
   QgsCurvePolygon *curvePoly = qgsgeometry_cast< QgsCurvePolygon * >( geom );
   QgsGeometryCollection *multiGeom = qgsgeometry_cast< QgsGeometryCollection * >( geom );
+  QgsPolyhedralSurface *polySurface = qgsgeometry_cast< QgsPolyhedralSurface * >( geom );
+
   if ( curvePoly )
   {
     polygonList.append( curvePoly );
   }
+  else if ( polySurface )
+  {
+    // PolyhedralSurface: collect all patches (which are QgsPolygon* that inherit from QgsCurvePolygon)
+    polygonList.reserve( polySurface->numPatches() );
+    for ( int i = 0; i < polySurface->numPatches(); ++i )
+    {
+      polygonList.append( polySurface->patchN( i ) );
+    }
+  }
   else if ( multiGeom )
   {
     polygonList.reserve( multiGeom->numGeometries() );
@@ -50,7 +64,7 @@ Qgis::GeometryOperationResult QgsGeometryEditUtils::addRing( QgsAbstractGeometry
   }
   else
   {
-    return Qgis::GeometryOperationResult::InvalidInputGeometryType; //not polygon / multipolygon;
+    return Qgis::GeometryOperationResult::InvalidInputGeometryType; //not polygon / multipolygon / polyhedral surface;
   }
 
   //ring must be closed
@@ -107,6 +121,91 @@ Qgis::GeometryOperationResult QgsGeometryEditUtils::addPart( QgsAbstractGeometry
     return Qgis::GeometryOperationResult::InvalidInputGeometryType;
   }
 
+  // Handle TIN - add triangle as patch
+  if ( QgsWkbTypes::flatType( geom->wkbType() ) == Qgis::WkbType::TIN )
+  {
+    QgsTriangulatedSurface *tin = qgsgeometry_cast<QgsTriangulatedSurface *>( geom );
+    if ( !tin )
+    {
+      return Qgis::GeometryOperationResult::InvalidBaseGeometry;
+    }
+
+    // Part can be a Triangle or a Polygon (that must be a triangle)
+    if ( QgsTriangle *triangle = qgsgeometry_cast<QgsTriangle *>( part.get() ) )
+    {
+      tin->addPatch( triangle->clone() );
+      return Qgis::GeometryOperationResult::Success;
+    }
+    else if ( QgsPolygon *polygon = qgsgeometry_cast<QgsPolygon *>( part.get() ) )
+    {
+      // Validate that the polygon can be converted to a triangle (3 vertices + closing point)
+      if ( polygon->exteriorRing() && polygon->exteriorRing()->numPoints() == 4 )
+      {
+        auto triangle = std::make_unique<QgsTriangle>();
+        triangle->setExteriorRing( polygon->exteriorRing()->clone() );
+        if ( !triangle->isEmpty() )
+        {
+          tin->addPatch( triangle.release() );
+          return Qgis::GeometryOperationResult::Success;
+        }
+      }
+      return Qgis::GeometryOperationResult::InvalidInputGeometryType;
+    }
+    else if ( QgsCurve *curve = qgsgeometry_cast<QgsCurve *>( part.get() ) )
+    {
+      // A closed curve with exactly 4 points (3 vertices + closing)
+      if ( curve->isClosed() && curve->numPoints() == 4 )
+      {
+        auto triangle = std::make_unique<QgsTriangle>();
+        triangle->setExteriorRing( curve->clone() );
+        if ( !triangle->isEmpty() )
+        {
+          tin->addPatch( triangle.release() );
+          return Qgis::GeometryOperationResult::Success;
+        }
+      }
+      return Qgis::GeometryOperationResult::InvalidInputGeometryType;
+    }
+    return Qgis::GeometryOperationResult::InvalidInputGeometryType;
+  }
+
+  // Handle PolyhedralSurface - add polygon as patch
+  if ( QgsWkbTypes::flatType( geom->wkbType() ) == Qgis::WkbType::PolyhedralSurface )
+  {
+    QgsPolyhedralSurface *polySurface = qgsgeometry_cast<QgsPolyhedralSurface *>( geom );
+    if ( !polySurface )
+    {
+      return Qgis::GeometryOperationResult::InvalidBaseGeometry;
+    }
+
+    // Part can be a Polygon or a CurvePolygon
+    if ( QgsPolygon *polygon = qgsgeometry_cast<QgsPolygon *>( part.get() ) )
+    {
+      polySurface->addPatch( polygon->clone() );
+      return Qgis::GeometryOperationResult::Success;
+    }
+    else if ( const QgsCurvePolygon *curvePolygon = qgsgeometry_cast<const QgsCurvePolygon *>( part.get() ) )
+    {
+      // Convert curve polygon to polygon
+      std::unique_ptr<QgsPolygon> polygon( curvePolygon->toPolygon() );
+      polySurface->addPatch( polygon.release() );
+      return Qgis::GeometryOperationResult::Success;
+    }
+    else if ( QgsCurve *curve = qgsgeometry_cast<QgsCurve *>( part.get() ) )
+    {
+      // A closed curve becomes a polygon patch
+      if ( curve->isClosed() && curve->numPoints() >= 4 )
+      {
+        auto polygon = std::make_unique<QgsPolygon>();
+        polygon->setExteriorRing( curve->clone() );
+        polySurface->addPatch( polygon.release() );
+        return Qgis::GeometryOperationResult::Success;
+      }
+      return Qgis::GeometryOperationResult::InvalidInputGeometryType;
+    }
+    return Qgis::GeometryOperationResult::InvalidInputGeometryType;
+  }
+
   //multitype?
   QgsGeometryCollection *geomCollection = qgsgeometry_cast<QgsGeometryCollection *>( geom );
   if ( !geomCollection )
diff --git a/src/gui/maptools/qgsmaptooldigitizefeature.cpp b/src/gui/maptools/qgsmaptooldigitizefeature.cpp
index 70e5803c6922..c89bd540c12c 100644
--- a/src/gui/maptools/qgsmaptooldigitizefeature.cpp
+++ b/src/gui/maptools/qgsmaptooldigitizefeature.cpp
@@ -80,13 +80,21 @@ void QgsMapToolDigitizeFeature::layerGeometryCaptured( const QgsGeometry &geomet
     {
       double defaultZ = QgsSettingsRegistryCore::settingsDigitizingDefaultZValue->value();
       double defaultM = QgsSettingsRegistryCore::settingsDigitizingDefaultMValue->value();
-      QVector<QgsGeometry> layerGeometries = geometry.coerceToType( layerWKBType, defaultZ, defaultM );
+      QVector<QgsGeometry> layerGeometries = geometry.coerceToType( layerWKBType, defaultZ, defaultM, true );
       if ( layerGeometries.count() > 0 )
         layerGeometry = layerGeometries.at( 0 );
 
       if ( layerGeometry.wkbType() != layerWKBType && layerGeometry.wkbType() != QgsWkbTypes::linearType( layerWKBType ) )
       {
-        emit messageEmitted( tr( "The digitized geometry type (%1) does not correspond to the layer geometry type (%2)." ).arg( QgsWkbTypes::displayString( layerGeometry.wkbType() ), QgsWkbTypes::displayString( layerWKBType ) ), Qgis::MessageLevel::Warning );
+        const QString coerceError = geometry.lastError();
+        if ( !coerceError.isEmpty() )
+        {
+          emit messageEmitted( coerceError, Qgis::MessageLevel::Warning );
+        }
+        else
+        {
+          emit messageEmitted( tr( "The digitized geometry type (%1) does not correspond to the layer geometry type (%2)." ).arg( QgsWkbTypes::displayString( layerGeometry.wkbType() ), QgsWkbTypes::displayString( layerWKBType ) ), Qgis::MessageLevel::Warning );
+        }
         return;
       }
     }
diff --git a/tests/src/core/geometry/testqgsgeometry.cpp b/tests/src/core/geometry/testqgsgeometry.cpp
index 1cd2ead43555..0a9683cd8521 100644
--- a/tests/src/core/geometry/testqgsgeometry.cpp
+++ b/tests/src/core/geometry/testqgsgeometry.cpp
@@ -38,6 +38,8 @@
 #include "qgslinestring.h"
 #include "qgspolygon.h"
 #include "qgstriangle.h"
+#include "qgstriangulatedsurface.h"
+#include "qgspolyhedralsurface.h"
 #include "qgsgeometryengine.h"
 #include "qgscircle.h"
 #include "qgsmultipoint.h"
@@ -178,6 +180,8 @@ class TestQgsGeometry : public QgsTest
 
     void chamferFillet();
 
+    void collectTinPatches();
+
   private:
     //! Must be called before each render test
     void initPainterTest();
@@ -3322,5 +3326,97 @@ void TestQgsGeometry::chamferFillet()
   QCOMPARE( g2.asWkt( 2 ), "MultiPolygon (((5 15, 10 15, 10 20, 5 20, 5 15)),((105 15, 108 15, 108.77 15.15, 109.41 15.59, 109.85 16.23, 110 17, 110 20, 105 20, 105 15)))" );
 }
 
+void TestQgsGeometry::collectTinPatches()
+{
+  QgsTriangle triangle1( QgsPoint( 0, 0, 0 ), QgsPoint( 1, 0, 0 ), QgsPoint( 0.5, 1, 0 ) );
+  QgsTriangle triangle2( QgsPoint( 1, 0, 0 ), QgsPoint( 2, 0, 0 ), QgsPoint( 1.5, 1, 0 ) );
+
+  QgsGeometry geom1( triangle1.clone() );
+  QgsGeometry geom2( triangle2.clone() );
+
+  QVector<QgsGeometry> geometries;
+  geometries << geom1 << geom2;
+
+  QgsGeometry result = QgsGeometry::collectTinPatches( geometries );
+
+  QVERIFY( !result.isNull() );
+
+  QVERIFY( result.wkbType() == Qgis::WkbType::TINZ );
+
+  const QgsTriangulatedSurface *tin = qgsgeometry_cast<const QgsTriangulatedSurface *>( result.constGet() );
+  QVERIFY( tin != nullptr );
+  QCOMPARE( tin->numPatches(), 2 );
+
+  // Test with mixed TIN and Triangle inputs
+  QgsTriangulatedSurface tinSurface;
+  QgsTriangle triangle3( QgsPoint( 2, 0, 0 ), QgsPoint( 3, 0, 0 ), QgsPoint( 2.5, 1, 0 ) );
+  tinSurface.addPatch( triangle3.clone() );
+
+  QgsGeometry geom3( tinSurface.clone() );
+  QgsGeometry geom4( triangle1.clone() );
+
+  QVector<QgsGeometry> mixedGeometries;
+  mixedGeometries << geom3 << geom4;
+
+  QgsGeometry mixedResult = QgsGeometry::collectTinPatches( mixedGeometries );
+  QVERIFY( !mixedResult.isNull() );
+  QVERIFY( mixedResult.wkbType() == Qgis::WkbType::TINZ );
+
+  const QgsTriangulatedSurface *mixedTin = qgsgeometry_cast<const QgsTriangulatedSurface *>( mixedResult.constGet() );
+  QVERIFY( mixedTin != nullptr );
+  QCOMPARE( mixedTin->numPatches(), 2 ); // 1 from the TIN + 1 from the triangle
+
+  // Test with null geometries
+  QgsGeometry nullGeom;
+  QVector<QgsGeometry> geometriesWithNull;
+  geometriesWithNull << geom1 << nullGeom << geom2;
+
+  QgsGeometry resultWithNull = QgsGeometry::collectTinPatches( geometriesWithNull );
+  QVERIFY( !resultWithNull.isNull() );
+  QVERIFY( resultWithNull.wkbType() == Qgis::WkbType::TINZ );
+
+  const QgsTriangulatedSurface *tinWithNull = qgsgeometry_cast<const QgsTriangulatedSurface *>( resultWithNull.constGet() );
+  QVERIFY( tinWithNull != nullptr );
+  QCOMPARE( tinWithNull->numPatches(), 2 ); // Should still have 2 patches
+
+  // Test with empty input
+  QVector<QgsGeometry> emptyGeometries;
+  QgsGeometry emptyResult = QgsGeometry::collectTinPatches( emptyGeometries );
+  QVERIFY( emptyResult.isNull() );
+
+  // Test with only null geometries
+  QVector<QgsGeometry> onlyNulls;
+  onlyNulls << nullGeom << nullGeom;
+  QgsGeometry onlyNullResult = QgsGeometry::collectTinPatches( onlyNulls );
+  QVERIFY( onlyNullResult.isNull() );
+
+  // Test with non-TIN/non-triangle geometries
+  QgsGeometry pointGeom = QgsGeometry::fromPointXY( QgsPointXY( 0, 0 ) );
+  QgsGeometry lineGeom = QgsGeometry::fromPolylineXY( QgsPolylineXY() << QgsPointXY( 0, 0 ) << QgsPointXY( 1, 1 ) );
+
+  QVector<QgsGeometry> nonTinGeometries;
+  nonTinGeometries << pointGeom << lineGeom;
+
+  QgsGeometry nonTinResult = QgsGeometry::collectTinPatches( nonTinGeometries );
+  QVERIFY( nonTinResult.isNull() );
+
+  // Test preserving Z and M values from first valid geometry
+  QgsTriangle triangleZM( QgsPoint( 0, 0, 10, 20 ), QgsPoint( 1, 0, 11, 21 ), QgsPoint( 0.5, 1, 12, 22 ) );
+  QgsGeometry geomZM( triangleZM.clone() );
+
+  QVector<QgsGeometry> zmGeometries;
+  zmGeometries << geomZM << geom1; // geom1 has no Z/M
+
+  QgsGeometry zmResult = QgsGeometry::collectTinPatches( zmGeometries );
+  QVERIFY( !zmResult.isNull() );
+  QCOMPARE( zmResult.wkbType(), Qgis::WkbType::TINZM );
+
+  const QgsTriangulatedSurface *zmTin = qgsgeometry_cast<const QgsTriangulatedSurface *>( zmResult.constGet() );
+  QVERIFY( zmTin != nullptr );
+  QCOMPARE( zmTin->numPatches(), 2 );
+  QVERIFY( zmTin->is3D() );
+  QVERIFY( zmTin->isMeasure() );
+}
+
 QGSTEST_MAIN( TestQgsGeometry )
 #include "testqgsgeometry.moc"
diff --git a/tests/src/core/geometry/testqgspolyhedralsurface.cpp b/tests/src/core/geometry/testqgspolyhedralsurface.cpp
index 612802745551..dbbf22ba283a 100644
--- a/tests/src/core/geometry/testqgspolyhedralsurface.cpp
+++ b/tests/src/core/geometry/testqgspolyhedralsurface.cpp
@@ -12,6 +12,7 @@
  *   (at your option) any later version.                                   *
  *                                                                         *
  ***************************************************************************/
+#include "qgsgeometry.h"
 #include "qgslinestring.h"
 #include "qgsmultilinestring.h"
 #include "qgsmultipolygon.h"
@@ -63,6 +64,8 @@ class TestQgsPolyhedralSurface : public QObject
     void testExport();
     void testCast();
     void testIsValid();
+    void testGeometryEditUtilsAddPart();
+    void testGeometryEditUtilsAddRing();
 };
 
 void TestQgsPolyhedralSurface::testConstructor()
@@ -1602,6 +1605,76 @@ void TestQgsPolyhedralSurface::testIsValid()
   QVERIFY( !isValid );
 }
 
+void TestQgsPolyhedralSurface::testGeometryEditUtilsAddPart()
+{
+  // Test Phase 2: QgsGeometry::addPartV2 for PolyhedralSurface
+
+  // Create an empty PolyhedralSurface geometry
+  QgsGeometry polySurfaceGeom( std::make_unique<QgsPolyhedralSurface>() );
+  QCOMPARE( qgsgeometry_cast<const QgsPolyhedralSurface *>( polySurfaceGeom.constGet() )->numPatches(), 0 );
+
+  // Add a polygon
+  QgsPolygon polygon1;
+  QgsLineString *ring1 = new QgsLineString();
+  ring1->setPoints( QgsPointSequence() << QgsPoint( 0, 0 ) << QgsPoint( 1, 0 ) << QgsPoint( 1, 1 ) << QgsPoint( 0, 1 ) << QgsPoint( 0, 0 ) );
+  polygon1.setExteriorRing( ring1 );
+
+  Qgis::GeometryOperationResult result = polySurfaceGeom.addPartV2( polygon1.clone(), Qgis::WkbType::PolyhedralSurface );
+  QCOMPARE( result, Qgis::GeometryOperationResult::Success );
+  QCOMPARE( qgsgeometry_cast<const QgsPolyhedralSurface *>( polySurfaceGeom.constGet() )->numPatches(), 1 );
+
+  // Add another polygon
+  QgsPolygon polygon2;
+  QgsLineString *ring2 = new QgsLineString();
+  ring2->setPoints( QgsPointSequence() << QgsPoint( 2, 0 ) << QgsPoint( 3, 0 ) << QgsPoint( 3, 1 ) << QgsPoint( 2, 1 ) << QgsPoint( 2, 0 ) );
+  polygon2.setExteriorRing( ring2 );
+
+  result = polySurfaceGeom.addPartV2( polygon2.clone(), Qgis::WkbType::PolyhedralSurface );
+  QCOMPARE( result, Qgis::GeometryOperationResult::Success );
+  QCOMPARE( qgsgeometry_cast<const QgsPolyhedralSurface *>( polySurfaceGeom.constGet() )->numPatches(), 2 );
+
+  // Add a closed curve (should be converted to polygon)
+  QgsLineString curve;
+  curve.setPoints( QgsPointSequence() << QgsPoint( 4, 0 ) << QgsPoint( 5, 0 ) << QgsPoint( 5, 1 ) << QgsPoint( 4, 1 ) << QgsPoint( 4, 0 ) );
+
+  result = polySurfaceGeom.addPartV2( curve.clone(), Qgis::WkbType::PolyhedralSurface );
+  QCOMPARE( result, Qgis::GeometryOperationResult::Success );
+  QCOMPARE( qgsgeometry_cast<const QgsPolyhedralSurface *>( polySurfaceGeom.constGet() )->numPatches(), 3 );
+}
+
+void TestQgsPolyhedralSurface::testGeometryEditUtilsAddRing()
+{
+  // Test Phase 3: QgsGeometry::addRing for PolyhedralSurface
+
+  // Create a PolyhedralSurface with one patch
+  QgsPolyhedralSurface polySurface;
+  QgsPolygon *patch = new QgsPolygon();
+  QgsLineString *exteriorRing = new QgsLineString();
+  exteriorRing->setPoints( QgsPointSequence() << QgsPoint( 0, 0 ) << QgsPoint( 10, 0 ) << QgsPoint( 10, 10 ) << QgsPoint( 0, 10 ) << QgsPoint( 0, 0 ) );
+  patch->setExteriorRing( exteriorRing );
+  polySurface.addPatch( patch );
+
+  QgsGeometry polySurfaceGeom( polySurface.clone() );
+  QCOMPARE( qgsgeometry_cast<const QgsPolyhedralSurface *>( polySurfaceGeom.constGet() )->numPatches(), 1 );
+  QCOMPARE( qgsgeometry_cast<const QgsPolyhedralSurface *>( polySurfaceGeom.constGet() )->patchN( 0 )->numInteriorRings(), 0 );
+
+  // Add a ring inside the patch
+  QgsLineString *innerRing = new QgsLineString();
+  innerRing->setPoints( QgsPointSequence() << QgsPoint( 2, 2 ) << QgsPoint( 8, 2 ) << QgsPoint( 8, 8 ) << QgsPoint( 2, 8 ) << QgsPoint( 2, 2 ) );
+
+  Qgis::GeometryOperationResult result = polySurfaceGeom.addRing( innerRing );
+  QCOMPARE( result, Qgis::GeometryOperationResult::Success );
+  QCOMPARE( qgsgeometry_cast<const QgsPolyhedralSurface *>( polySurfaceGeom.constGet() )->patchN( 0 )->numInteriorRings(), 1 );
+
+  // Try to add a ring outside all patches - should fail
+  QgsLineString *outerRing = new QgsLineString();
+  outerRing->setPoints( QgsPointSequence() << QgsPoint( 20, 20 ) << QgsPoint( 30, 20 ) << QgsPoint( 30, 30 ) << QgsPoint( 20, 30 ) << QgsPoint( 20, 20 ) );
+
+  result = polySurfaceGeom.addRing( outerRing );
+  QCOMPARE( result, Qgis::GeometryOperationResult::AddRingNotInExistingFeature );
+  QCOMPARE( qgsgeometry_cast<const QgsPolyhedralSurface *>( polySurfaceGeom.constGet() )->patchN( 0 )->numInteriorRings(), 1 ); // unchanged
+}
+
 
 QGSTEST_MAIN( TestQgsPolyhedralSurface )
 #include "testqgspolyhedralsurface.moc"
diff --git a/tests/src/core/geometry/testqgstriangulatedsurface.cpp b/tests/src/core/geometry/testqgstriangulatedsurface.cpp
index 82d2bb42a47c..1ca220fc9eeb 100644
--- a/tests/src/core/geometry/testqgstriangulatedsurface.cpp
+++ b/tests/src/core/geometry/testqgstriangulatedsurface.cpp
@@ -12,6 +12,7 @@
  *   (at your option) any later version.                                   *
  *                                                                         *
  ***************************************************************************/
+#include "qgsgeometry.h"
 #include "qgslinestring.h"
 #include "qgspolygon.h"
 #include "qgssurface.h"
@@ -58,6 +59,8 @@ class TestQgsTriangulatedSurface : public QObject
     void testWKT();
     void testExport();
     void testCast();
+    void testCoerceToTypeErrorMessage();
+    void testGeometryEditUtilsAddPart();
 };
 
 void TestQgsTriangulatedSurface::testConstructor()
@@ -1125,6 +1128,74 @@ void TestQgsTriangulatedSurface::testCast()
   QVERIFY( !pCast2.fromWkt( u"TINZ((111111))"_s ) );
 }
 
+void TestQgsTriangulatedSurface::testCoerceToTypeErrorMessage()
+{
+  // Test Phase 1: coerceToType should return error message when polygon has too many vertices for TIN
+
+  // Create a polygon with 4 vertices (5 points including closing) - too many for a triangle
+  QgsPolygon polygon;
+  QgsLineString *exteriorRing = new QgsLineString();
+  exteriorRing->setPoints( QgsPointSequence() << QgsPoint( 0, 0 ) << QgsPoint( 1, 0 ) << QgsPoint( 1, 1 ) << QgsPoint( 0, 1 ) << QgsPoint( 0, 0 ) );
+  polygon.setExteriorRing( exteriorRing );
+  QgsGeometry geom( polygon.clone() );
+
+  QVector<QgsGeometry> result = geom.coerceToType( Qgis::WkbType::TIN, 0, 0, true );
+
+  // Should fail with empty result
+  QVERIFY( result.isEmpty() );
+
+  // Test with a valid triangle (3 vertices = 4 points including closing)
+  QgsPolygon trianglePolygon;
+  QgsLineString *triangleRing = new QgsLineString();
+  triangleRing->setPoints( QgsPointSequence() << QgsPoint( 0, 0 ) << QgsPoint( 1, 0 ) << QgsPoint( 0.5, 1 ) << QgsPoint( 0, 0 ) );
+  trianglePolygon.setExteriorRing( triangleRing );
+  QgsGeometry triangleGeom( trianglePolygon.clone() );
+
+  result = triangleGeom.coerceToType( Qgis::WkbType::TIN, 0, 0, true );
+
+  // Should succeed
+  QVERIFY( !result.isEmpty() );
+}
+
+void TestQgsTriangulatedSurface::testGeometryEditUtilsAddPart()
+{
+  // Test Phase 2: QgsGeometry::addPartV2 for TIN
+
+  // Create an empty TIN geometry
+  QgsGeometry tinGeom( std::make_unique<QgsTriangulatedSurface>() );
+  QCOMPARE( qgsgeometry_cast<const QgsTriangulatedSurface *>( tinGeom.constGet() )->numPatches(), 0 );
+
+  // Add a triangle
+  QgsTriangle triangle1( QgsPoint( 0, 0 ), QgsPoint( 1, 0 ), QgsPoint( 0.5, 1 ) );
+  Qgis::GeometryOperationResult result = tinGeom.addPartV2( triangle1.clone(), Qgis::WkbType::TIN );
+  QCOMPARE( result, Qgis::GeometryOperationResult::Success );
+  QCOMPARE( qgsgeometry_cast<const QgsTriangulatedSurface *>( tinGeom.constGet() )->numPatches(), 1 );
+
+  // Add another triangle
+  QgsTriangle triangle2( QgsPoint( 1, 0 ), QgsPoint( 2, 0 ), QgsPoint( 1.5, 1 ) );
+  result = tinGeom.addPartV2( triangle2.clone(), Qgis::WkbType::TIN );
+  QCOMPARE( result, Qgis::GeometryOperationResult::Success );
+  QCOMPARE( qgsgeometry_cast<const QgsTriangulatedSurface *>( tinGeom.constGet() )->numPatches(), 2 );
+
+  // Try to add a polygon that is a valid triangle (3 vertices)
+  QgsPolygon validPolygon;
+  QgsLineString *ring = new QgsLineString();
+  ring->setPoints( QgsPointSequence() << QgsPoint( 2, 0 ) << QgsPoint( 3, 0 ) << QgsPoint( 2.5, 1 ) << QgsPoint( 2, 0 ) );
+  validPolygon.setExteriorRing( ring );
+  result = tinGeom.addPartV2( validPolygon.clone(), Qgis::WkbType::TIN );
+  QCOMPARE( result, Qgis::GeometryOperationResult::Success );
+  QCOMPARE( qgsgeometry_cast<const QgsTriangulatedSurface *>( tinGeom.constGet() )->numPatches(), 3 );
+
+  // Try to add a polygon that is NOT a triangle (4 vertices) - should fail
+  QgsPolygon invalidPolygon;
+  ring = new QgsLineString();
+  ring->setPoints( QgsPointSequence() << QgsPoint( 0, 0 ) << QgsPoint( 1, 0 ) << QgsPoint( 1, 1 ) << QgsPoint( 0, 1 ) << QgsPoint( 0, 0 ) );
+  invalidPolygon.setExteriorRing( ring );
+  result = tinGeom.addPartV2( invalidPolygon.clone(), Qgis::WkbType::TIN );
+  QCOMPARE( result, Qgis::GeometryOperationResult::InvalidInputGeometryType );
+  QCOMPARE( qgsgeometry_cast<const QgsTriangulatedSurface *>( tinGeom.constGet() )->numPatches(), 3 ); // unchanged
+}
+
 
 QGSTEST_MAIN( TestQgsTriangulatedSurface )
 #include "testqgstriangulatedsurface.moc"
diff --git a/tests/src/python/test_qgsgeometry.py b/tests/src/python/test_qgsgeometry.py
index 0e77d553e04f..09c999238883 100644
--- a/tests/src/python/test_qgsgeometry.py
+++ b/tests/src/python/test_qgsgeometry.py
@@ -12488,6 +12488,96 @@ def coerce_to_wkt(
             ["PolyhedralSurface Z (((1 1 2, 1 2 2, 2 2 3, 5 5 3, 1 1 2)))"],
         )
 
+        # Polygon/Triangle to TIN
+        self.assertEqual(
+            coerce_to_wkt(
+                "Polygon ((1 1, 1 2, 2 2, 1 1))",
+                QgsWkbTypes.Type.TIN,
+            ),
+            ["TIN (((1 1, 1 2, 2 2, 1 1)))"],
+        )
+        self.assertEqual(
+            coerce_to_wkt(
+                "Polygon Z((1 1 0, 1 2 0, 2 2 0, 1 1 0))",
+                QgsWkbTypes.Type.TINZ,
+            ),
+            ["TIN Z (((1 1 0, 1 2 0, 2 2 0, 1 1 0)))"],
+        )
+        self.assertEqual(
+            coerce_to_wkt(
+                "Triangle ((1 1, 1 2, 2 2, 1 1))",
+                QgsWkbTypes.Type.TIN,
+            ),
+            ["TIN (((1 1, 1 2, 2 2, 1 1)))"],
+        )
+        self.assertEqual(
+            coerce_to_wkt(
+                "MultiPolygon (((1 1, 1 2, 2 2, 1 1)),((3 3, 4 3, 4 4, 3 3)))",
+                QgsWkbTypes.Type.TIN,
+            ),
+            ["TIN (((1 1, 1 2, 2 2, 1 1)),((3 3, 4 3, 4 4, 3 3)))"],
+        )
+
+        # PolyhedralSurface to MultiPolygon
+        self.assertEqual(
+            coerce_to_wkt(
+                "PolyhedralSurface (((1 1, 1 2, 2 2, 1 1)),((3 3, 4 3, 4 4, 3 3)))",
+                QgsWkbTypes.Type.MultiPolygon,
+            ),
+            ["MultiPolygon (((1 1, 1 2, 2 2, 1 1)),((3 3, 4 3, 4 4, 3 3)))"],
+        )
+        self.assertEqual(
+            coerce_to_wkt(
+                "PolyhedralSurface Z (((1 1 0, 1 2 0, 2 2 0, 1 1 0)),((3 3 0, 4 3 0, 4 4 0, 3 3 0)))",
+                QgsWkbTypes.Type.MultiPolygonZ,
+            ),
+            [
+                "MultiPolygon Z (((1 1 0, 1 2 0, 2 2 0, 1 1 0)),((3 3 0, 4 3 0, 4 4 0, 3 3 0)))"
+            ],
+        )
+        # PolyhedralSurface to Polygon (single patch)
+        self.assertEqual(
+            coerce_to_wkt(
+                "PolyhedralSurface (((1 1, 1 2, 2 2, 1 1)))",
+                QgsWkbTypes.Type.Polygon,
+            ),
+            ["Polygon ((1 1, 1 2, 2 2, 1 1))"],
+        )
+        # PolyhedralSurface to Polygon (multi patches -> multiple results)
+        self.assertEqual(
+            coerce_to_wkt(
+                "PolyhedralSurface (((1 1, 1 2, 2 2, 1 1)),((3 3, 4 3, 4 4, 3 3)))",
+                QgsWkbTypes.Type.Polygon,
+            ),
+            ["Polygon ((1 1, 1 2, 2 2, 1 1))", "Polygon ((3 3, 4 3, 4 4, 3 3))"],
+        )
+
+        # TIN to MultiPolygon
+        self.assertEqual(
+            coerce_to_wkt(
+                "TIN (((1 1, 1 2, 2 2, 1 1)),((3 3, 4 3, 4 4, 3 3)))",
+                QgsWkbTypes.Type.MultiPolygon,
+            ),
+            ["MultiPolygon (((1 1, 1 2, 2 2, 1 1)),((3 3, 4 3, 4 4, 3 3)))"],
+        )
+        self.assertEqual(
+            coerce_to_wkt(
+                "TIN Z (((1 1 0, 1 2 0, 2 2 0, 1 1 0)),((3 3 0, 4 3 0, 4 4 0, 3 3 0)))",
+                QgsWkbTypes.Type.MultiPolygonZ,
+            ),
+            [
+                "MultiPolygon Z (((1 1 0, 1 2 0, 2 2 0, 1 1 0)),((3 3 0, 4 3 0, 4 4 0, 3 3 0)))"
+            ],
+        )
+        # TIN to Polygon (single patch)
+        self.assertEqual(
+            coerce_to_wkt(
+                "TIN (((1 1, 1 2, 2 2, 1 1)))",
+                QgsWkbTypes.Type.Polygon,
+            ),
+            ["Polygon ((1 1, 1 2, 2 2, 1 1))"],
+        )
+
         # GeometryCollection of Point to MultiPoint
         self.assertEqual(
             coerce_to_wkt(