gdal vector buffer: automatically set output geometry field type to Polygon or MultiPolygon

Fixes #13512

Author: rouault

apps/gdalalg_vector_buffer.cpp

@@ -72,8 +72,24 @@ class GDALVectorBufferAlgorithmLayer final
     GDALVectorBufferAlgorithmLayer(
         OGRLayer &oSrcLayer, const GDALVectorBufferAlgorithm::Options &opts)
         : GDALVectorGeomOneToOneAlgorithmLayer<GDALVectorBufferAlgorithm>(
-              oSrcLayer, opts)
+              oSrcLayer, opts),
+          m_poFeatureDefn(oSrcLayer.GetLayerDefn()->Clone())
     {
+        m_poFeatureDefn->Reference();
+        for (int i = 0; i < m_poFeatureDefn->GetGeomFieldCount(); ++i)
+        {
+            if (IsSelectedGeomField(i))
+            {
+                auto poGeomFieldDefn = m_poFeatureDefn->GetGeomFieldDefn(i);
+                const auto eType = wkbFlatten(poGeomFieldDefn->GetType());
+                if (eType == wkbUnknown ||
+                    OGR_GT_IsSubClassOf(eType, wkbGeometryCollection))
+                    poGeomFieldDefn->SetType(wkbMultiPolygon);
+                else
+                    poGeomFieldDefn->SetType(wkbPolygon);
+            }
+        }
+
         m_aosBufferOptions.SetNameValue("ENDCAP_STYLE",
                                         opts.m_endCapStyle.c_str());
         m_aosBufferOptions.SetNameValue("JOIN_STYLE", opts.m_joinStyle.c_str());
@@ -85,6 +101,16 @@ class GDALVectorBufferAlgorithmLayer final
                                         m_opts.m_side != "both" ? "YES" : "NO");
     }
 
+    ~GDALVectorBufferAlgorithmLayer() override
+    {
+        m_poFeatureDefn->Release();
+    }
+
+    const OGRFeatureDefn *GetLayerDefn() const override
+    {
+        return m_poFeatureDefn;
+    }
+
   protected:
     using GDALVectorGeomOneToOneAlgorithmLayer::TranslateFeature;
 
@@ -93,6 +119,9 @@ class GDALVectorBufferAlgorithmLayer final
 
   private:
     CPLStringList m_aosBufferOptions{};
+    OGRFeatureDefn *const m_poFeatureDefn;
+
+    CPL_DISALLOW_COPY_ASSIGN(GDALVectorBufferAlgorithmLayer)
 };
 
 /************************************************************************/
@@ -102,7 +131,7 @@ class GDALVectorBufferAlgorithmLayer final
 std::unique_ptr<OGRFeature> GDALVectorBufferAlgorithmLayer::TranslateFeature(
     std::unique_ptr<OGRFeature> poSrcFeature) const
 {
-    const int nGeomFieldCount = poSrcFeature->GetGeomFieldCount();
+    const int nGeomFieldCount = m_poFeatureDefn->GetGeomFieldCount();
     for (int i = 0; i < nGeomFieldCount; ++i)
     {
         if (IsSelectedGeomField(i))
@@ -114,15 +143,22 @@ std::unique_ptr<OGRFeature> GDALVectorBufferAlgorithmLayer::TranslateFeature(
                                               m_aosBufferOptions.List()));
                 if (poGeom)
                 {
-                    poGeom->assignSpatialReference(m_srcLayer.GetLayerDefn()
-                                                       ->GetGeomFieldDefn(i)
-                                                       ->GetSpatialRef());
-                    poSrcFeature->SetGeomField(i, std::move(poGeom));
+                    const auto poGeomFielDefn =
+                        m_poFeatureDefn->GetGeomFieldDefn(i);
+                    poGeom.reset(OGRGeometryFactory::forceTo(
+                        poGeom.release(), poGeomFielDefn->GetType()));
+                    if (poGeom)
+                    {
+                        poGeom->assignSpatialReference(
+                            poGeomFielDefn->GetSpatialRef());
+                        poSrcFeature->SetGeomField(i, std::move(poGeom));
+                    }
                 }
             }
         }
     }
 
+    poSrcFeature->SetFDefnUnsafe(m_poFeatureDefn);
     return poSrcFeature;
 }
 

autotest/utilities/test_gdalalg_vector_buffer.py

@@ -57,9 +57,9 @@ def get_alg():
             "POLYGON ((1 0,0 0,0 1,1 1,1 0))",
         ),
         (
-            "LINESTRING (0 0,1 0)",
+            "MULTILINESTRING ((0 0,1 0))",
             {"distance": 1, "side": "right"},
-            "POLYGON ((0 0,1 0,1 -1,0 -1,0 0))",
+            "MULTIPOLYGON (((0 0,1 0,1 -1,0 -1,0 0)))",
         ),
     ],
     ids=[
@@ -78,10 +78,11 @@ def test_gdalalg_vector_buffer(input_wkt, options, output_wkt):
     src_ds = gdal.GetDriverByName("MEM").Create("", 0, 0, 0, gdal.GDT_Unknown)
     srs = osr.SpatialReference()
     srs.ImportFromEPSG(32631)
-    src_lyr = src_ds.CreateLayer("the_layer", srs=srs)
+    geom = ogr.CreateGeometryFromWkt(input_wkt)
+    src_lyr = src_ds.CreateLayer("the_layer", srs=srs, geom_type=geom.GetGeometryType())
 
     f = ogr.Feature(src_lyr.GetLayerDefn())
-    f.SetGeometry(ogr.CreateGeometryFromWkt(input_wkt))
+    f.SetGeometry(geom)
     src_lyr.CreateFeature(f)
 
     f = ogr.Feature(src_lyr.GetLayerDefn())
@@ -99,6 +100,8 @@ def test_gdalalg_vector_buffer(input_wkt, options, output_wkt):
     out_ds = alg["output"].GetDataset()
     out_lyr = out_ds.GetLayer(0)
     out_f = out_lyr.GetNextFeature()
+    assert out_lyr.GetLayerDefn().IsSame(out_f.GetDefnRef())
+    assert out_lyr.GetGeomType() == out_f.GetGeometryRef().GetGeometryType()
     # print(out_f.GetGeometryRef().ExportToIsoWkt())
     ogrtest.check_feature_geometry(out_f, output_wkt)
     assert (