Merge pull request #509 from peterstace/geos_unary_union

Wrap GEOS's Unary Union

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## Unreleased
+
+- Adds a wrapper in the `geos` package for the `GEOSUnaryUnion_r` function
+  (exposed as `UnaryUnion`).
+
 ## v0.42.1
 
 2023-05-05

geos/entrypoints.go

@@ -373,3 +373,13 @@ func CoverageUnion(g geom.Geometry, opts ...geom.ConstructorOption) (geom.Geomet
 	})
 	return result, wrap(err, "executing GEOSCoverageUnion_r")
 }
+
+// UnaryUnion is a single argument version of Union. It is most useful when
+// supplied with a GeometryCollection, resulting in the union of the
+// GeometryCollection's child geometries.
+func UnaryUnion(g geom.Geometry, opts ...geom.ConstructorOption) (geom.Geometry, error) {
+	result, err := unaryOpG(g, opts, func(ctx C.GEOSContextHandle_t, g *C.GEOSGeometry) *C.GEOSGeometry {
+		return C.GEOSUnaryUnion_r(ctx, g)
+	})
+	return result, wrap(err, "executing GEOSUnaryUnion_r")
+}

geos/entrypoints_test.go

@@ -830,6 +830,24 @@ func TestMakeValid(t *testing.T) {
 	}
 }
 
+func TestUnaryUnion(t *testing.T) {
+	for i, tt := range []struct {
+		input      string
+		wantOutput string
+	}{
+		{
+			"GEOMETRYCOLLECTION(POLYGON((0 0,0 2,2 2,2 0,0 0)),POLYGON((1 1,1 3,3 3,3 1,1 1)))",
+			"POLYGON((0 0,2 0,2 1,3 1,3 3,1 3,1 2,0 2,0 0))",
+		},
+	} {
+		t.Run(strconv.Itoa(i), func(t *testing.T) {
+			got, err := UnaryUnion(geomFromWKT(t, tt.input))
+			expectNoErr(t, err)
+			expectGeomEq(t, got, geomFromWKT(t, tt.wantOutput), geom.IgnoreOrder)
+		})
+	}
+}
+
 func TestCoverageUnion(t *testing.T) {
 	for i, tc := range []struct {
 		input   string