Properly support signed/unsigned field types for GeoTIFF tags

* Particularly noticeable for sample min/max metadata
Unidata · May 6, 2024 · b5a17bb · b5a17bb
1 parent bdc03af
commit b5a17bb
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Showing 3 changed files with 24 additions and 7 deletions.
diff --git a/cdm/misc/src/main/java/ucar/nc2/geotiff/GeotiffWriter.java b/cdm/misc/src/main/java/ucar/nc2/geotiff/GeotiffWriter.java
@@ -335,14 +335,14 @@ private void writeMetadata(boolean greyScale, double xStart, double yStart, doub
         FieldType ftype;
         DataType sdtype = dtype.withSignedness(DataType.Signedness.SIGNED);
         if (sdtype == DataType.BYTE) {
-          ftype = FieldType.BYTE;
+          ftype = dtype.isUnsigned() ? FieldType.BYTE : FieldType.SBYTE;
         } else if (sdtype == DataType.SHORT) {
-          ftype = FieldType.SHORT;
+          ftype = dtype.isUnsigned() ? FieldType.SHORT : FieldType.SSHORT;
         } else if (sdtype == DataType.INT) {
-          // A geotiff LONG is really a 4-byte regular integer
-          ftype = FieldType.LONG;
+          // A geotiff LONG/SLONG is really a 4-byte regular integer
+          ftype = dtype.isUnsigned() ? FieldType.LONG : FieldType.SLONG;
         } else {
-          throw new IllegalArgumentException("Unsupported dtype: " + dtype + " sdtype: " + sdtype);
+          throw new IllegalArgumentException("Unsupported dtype: " + dtype);
         }
         geotiff.addTag(new IFDEntry(Tag.SMinSampleValue, ftype).setValue(min));
         geotiff.addTag(new IFDEntry(Tag.SMaxSampleValue, ftype).setValue(max));

diff --git a/cdm/misc/src/test/data/ucar/nc2/geotiff/baseline_palette.tif b/cdm/misc/src/test/data/ucar/nc2/geotiff/baseline_palette.tif
diff --git a/cdm/misc/src/test/java/ucar/nc2/geotiff/TestGeoTiffPalette.java b/cdm/misc/src/test/java/ucar/nc2/geotiff/TestGeoTiffPalette.java
@@ -28,7 +28,7 @@
  * Testing the color palette features of GeotiffWriter
  *
  * @author WeatherGod
- * @since 8/12/20224
+ * @since 8/12/2022
  */
 public class TestGeoTiffPalette {
   private static final Logger logger = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
@@ -150,9 +150,26 @@ public void testWritePalette() throws IOException {
         Assert.assertNotNull(colorTableTag);
         Assert.assertEquals(3 * 256, colorTableTag.count);
         Assert.assertArrayEquals(colorTable, colorTableTag.value);
+
+        IFDEntry sMinTag = geotiff.findTag(Tag.SMinSampleValue);
+        Assert.assertNotNull(sMinTag);
+        Assert.assertEquals(FieldType.BYTE, sMinTag.type);
+        Assert.assertEquals(1, sMinTag.count);
+        Assert.assertEquals(1, sMinTag.value[0]);
+
+        IFDEntry sMaxTag = geotiff.findTag(Tag.SMaxSampleValue);
+        Assert.assertNotNull(sMaxTag);
+        Assert.assertEquals(FieldType.BYTE, sMaxTag.type);
+        Assert.assertEquals(1, sMaxTag.count);
+        Assert.assertEquals(255, sMaxTag.value[0]);
+
+        // When doing a color paletted geotiff, no assumption is made
+        // about the NoData value and is therefore not encoded.
+        IFDEntry noDataTag = geotiff.findTag(Tag.GDALNoData);
+        Assert.assertNull(noDataTag);
       }
 
-      // compare file s are equal
+      // compare files are equal
       File file1 = new File(gridOut);
       File file2 = new File(baseline);