Merge pull request #619 from peterstace/bugfix_Coordinate_type_not_re…

…tained_for_simplified_empty_geometries Retain coordinate type for empty simplified geometries
peterstace · May 23, 2024 · 5ae7add · 5ae7add
2 parents 5f64efe + 098d1ec
commit 5ae7add
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -7,6 +7,9 @@
 - Fixes a bug where geometry collections with mixed coordinate types were
   erroneously allowed during WKT and WKB parsing.
 
+- Fixes a bug where the `Simplify` method would drop coordinate type to XY in
+  some scenarios where the result is an empty geometry.
+
 ## v0.50.0
 
 2024-05-07

diff --git a/geom/alg_simplify_test.go b/geom/alg_simplify_test.go
@@ -88,6 +88,30 @@ func TestSimplify(t *testing.T) {
 		{"POLYGON Z((2 2 10,2 3 20,3 3 30,3 2 40,2 2 10))", 0.0, "POLYGON Z((2 2 10,2 3 20,3 3 30,3 2 40,2 2 10))"},
 		{"POLYGON M((2 2 10,2 3 20,3 3 30,3 2 40,2 2 10))", 0.0, "POLYGON M((2 2 10,2 3 20,3 3 30,3 2 40,2 2 10))"},
 		{"POLYGON ZM((2 2 10 11,2 3 20 21,3 3 30 31,3 2 40 41,2 2 10 11))", 0.0, "POLYGON ZM((2 2 10 11,2 3 20 21,3 3 30 31,3 2 40 41,2 2 10 11))"},
+
+		// Empty Z, M, ZM
+		{"POINT Z EMPTY", 0.1, "POINT Z EMPTY"},
+		{"POINT M EMPTY", 0.1, "POINT M EMPTY"},
+		{"POINT ZM EMPTY", 0.1, "POINT ZM EMPTY"},
+		{"LINESTRING Z EMPTY", 0.1, "LINESTRING Z EMPTY"},
+		{"LINESTRING M EMPTY", 0.1, "LINESTRING M EMPTY"},
+		{"LINESTRING ZM EMPTY", 0.1, "LINESTRING ZM EMPTY"},
+		{"POLYGON Z EMPTY", 0.1, "POLYGON Z EMPTY"},
+		{"POLYGON M EMPTY", 0.1, "POLYGON M EMPTY"},
+		{"POLYGON ZM EMPTY", 0.1, "POLYGON ZM EMPTY"},
+		{"MULTIPOINT Z EMPTY", 0.1, "MULTIPOINT Z EMPTY"},
+		{"MULTIPOINT M EMPTY", 0.1, "MULTIPOINT M EMPTY"},
+		{"MULTIPOINT ZM EMPTY", 0.1, "MULTIPOINT ZM EMPTY"},
+		{"MULTILINESTRING Z EMPTY", 0.1, "MULTILINESTRING Z EMPTY"},
+		{"MULTILINESTRING M EMPTY", 0.1, "MULTILINESTRING M EMPTY"},
+		{"MULTILINESTRING ZM EMPTY", 0.1, "MULTILINESTRING ZM EMPTY"},
+		{"MULTIPOLYGON Z EMPTY", 0.1, "MULTIPOLYGON Z EMPTY"},
+		{"MULTIPOLYGON M EMPTY", 0.1, "MULTIPOLYGON M EMPTY"},
+		{"MULTIPOLYGON ZM EMPTY", 0.1, "MULTIPOLYGON ZM EMPTY"},
+		{"GEOMETRYCOLLECTION Z EMPTY", 0.1, "GEOMETRYCOLLECTION Z EMPTY"},
+		{"GEOMETRYCOLLECTION M EMPTY", 0.1, "GEOMETRYCOLLECTION M EMPTY"},
+		{"GEOMETRYCOLLECTION ZM EMPTY", 0.1, "GEOMETRYCOLLECTION ZM EMPTY"},
+		{"GEOMETRYCOLLECTION EMPTY", 0.1, "GEOMETRYCOLLECTION EMPTY"},
 	} {
 		t.Run(strconv.Itoa(i), func(t *testing.T) {
 			in := geomFromWKT(t, tc.input)

diff --git a/geom/type_geometry_collection.go b/geom/type_geometry_collection.go
@@ -550,7 +550,7 @@ func (c GeometryCollection) Simplify(threshold float64, nv ...NoValidate) (Geome
 			return GeometryCollection{}, wrapSimplified(err)
 		}
 	}
-	return NewGeometryCollection(geoms), nil
+	return NewGeometryCollection(geoms).ForceCoordinatesType(c.CoordinatesType()), nil
 }
 
 // Densify returns a new GeometryCollection with additional linearly

diff --git a/geom/type_multi_line_string.go b/geom/type_multi_line_string.go
@@ -508,7 +508,7 @@ func (m MultiLineString) Simplify(threshold float64) MultiLineString {
 			lss = append(lss, ls)
 		}
 	}
-	return NewMultiLineString(lss)
+	return NewMultiLineString(lss).ForceCoordinatesType(m.CoordinatesType())
 }
 
 // Densify returns a new MultiLineString with additional linearly interpolated

diff --git a/geom/type_multi_polygon.go b/geom/type_multi_polygon.go
@@ -567,7 +567,7 @@ func (m MultiPolygon) Simplify(threshold float64, nv ...NoValidate) (MultiPolygo
 			return MultiPolygon{}, wrapSimplified(err)
 		}
 	}
-	return simpl, nil
+	return simpl.ForceCoordinatesType(m.CoordinatesType()), nil
 }
 
 // Densify returns a new MultiPolygon with additional linearly interpolated

diff --git a/geom/type_polygon.go b/geom/type_polygon.go
@@ -661,7 +661,7 @@ func (p Polygon) Simplify(threshold float64, nv ...NoValidate) (Polygon, error)
 		return ring.Coordinates().Length() < 4
 	}
 	if hasCollapsed(exterior) {
-		return Polygon{}, nil
+		return Polygon{}.ForceCoordinatesType(p.CoordinatesType()), nil
 	}
 
 	n := p.NumInteriorRings()