Merge pull request #11343 from rouault/fix_11340

GDALContourGenerateEx(): return CE_None even if the raster is at constant value

alg/contour.cpp

@@ -710,7 +710,7 @@ CPLErr GDALContourGenerateEx(GDALRasterBandH hBand, void *hLayer,
         }
     }
 
-    bool ok = false;
+    bool ok = true;
 
     try
     {
@@ -880,6 +880,11 @@ CPLErr GDALContourGenerateEx(GDALRasterBandH hBand, void *hLayer,
         }
     }
 
+    if (ok)
+    {
+        pfnProgress(1.0, "", pProgressArg);
+    }
+
     return ok ? CE_None : CE_Failure;
 }
 

autotest/alg/contour.py

@@ -446,3 +446,28 @@ def test_contour_min_value_is_multiple_of_interval(tmp_vsimem):
     f = lyr.GetNextFeature()
     assert f["ELEV"] == 3
     ogrtest.check_feature_geometry(f, "LINESTRING (1.5 0.0,1.5 0.5,1.5 1.5,1.5 2.0)")
+
+
+###############################################################################
+# Test scenario of https://github.com/OSGeo/gdal/issues/11340
+
+
+def test_contour_constant_raster_value(tmp_vsimem):
+
+    ogr_ds = ogr.GetDriverByName("Memory").CreateDataSource("")
+    lyr = ogr_ds.CreateLayer("contour", geom_type=ogr.wkbLineString)
+    lyr.CreateField(ogr.FieldDefn("ID", ogr.OFTInteger))
+    lyr.CreateField(ogr.FieldDefn("ELEV", ogr.OFTReal))
+
+    src_ds = gdal.GetDriverByName("MEM").Create("", 1, 1)
+    assert (
+        gdal.ContourGenerateEx(
+            src_ds.GetRasterBand(1),
+            lyr,
+            options=["LEVEL_INTERVAL=10", "ID_FIELD=0", "ELEV_FIELD=1"],
+        )
+        == gdal.CE_None
+    )
+
+    f = lyr.GetNextFeature()
+    assert f is None