add example fast_simpl.py in #992

docs/changes.md

@@ -33,6 +33,7 @@ point in the same cloud of points.
 - add `transformations.TransformInterpolator` class
 - add `Line.find_index_at_position()` finds the index of the line vertex that is closest to a point
 - add `visual.LightKit` class which provides "natural" lighting from 4 sources.
+- add `fast-simplification` example by @Louis-Pujol in #992
 
 
 ## Breaking changes
@@ -65,6 +66,7 @@ examples/pyplot/plot_stream.py
 examples/other/madcad1.py
 examples/other/tetgen1.py
 examples/other/nelder-mead.py
+examples/other/fast_simpl.py
 
 tests/issues/issue_968.py
 tests/snippets/test_discourse_1956.py

examples/other/fast_simpl.py

@@ -0,0 +1,36 @@
+"""Use fast-simplification to decimate a mesh and transfer
+data defined on the original faces to the decimated ones."""
+# Credits: Louis Pujol
+# https://github.com/pyvista/fast-simplification
+# pip install fast-simplification
+import numpy as np
+import fast_simplification as fs
+import vedo
+
+# Load a mesh and define a signal on vertices
+mesh = vedo.Sphere().lw(1)
+points = mesh.vertices
+faces = mesh.cells
+signal = points[:, 2]
+mesh.pointdata["signal"] = signal
+
+# Decimate the mesh and compute the mapping between the original vertices
+# and the decimated ones with fast-simplification
+points_decim, faces_decim, collapses = fs.simplify(
+    points, faces, target_reduction=0.9, return_collapses=True
+)
+points_decim, faces_decim, index_mapping = fs.replay_simplification(
+    points, faces, collapses
+)
+
+# Compute the average of the signal on the decimated vertices (scatter operation)
+unique_values, counts = np.unique(index_mapping, return_counts=True)
+a = np.zeros(len(unique_values), dtype=signal.dtype)
+np.add.at(a, index_mapping, signal)  # scatter addition
+a /= counts  # divide by the counts of each vertex index to get the average
+
+# Create a new mesh with the decimated vertices and the averaged signal
+decimated_mesh = vedo.Mesh([points_decim, faces_decim]).lw(1)
+decimated_mesh.pointdata["signal"] = a
+
+vedo.show(mesh, decimated_mesh, N=2, axes=1).close()