smartclip: implicitly close rings that have endpoints in the bound

clip/smartclip/smart.go

@@ -11,7 +11,8 @@ import (
 )
 
 // Geometry will do a smart more involved clipping and wrapping of the geometry.
-// It will return simple OGC geometries.
+// It will return simple OGC geometries. Rings that are NOT closed AND have an
+// endpoint in the bound will be implicitly closed.
 func Geometry(box orb.Bound, g orb.Geometry, o orb.Orientation) orb.Geometry {
 	if g == nil {
 		return nil
@@ -61,7 +62,8 @@ func Geometry(box orb.Bound, g orb.Geometry, o orb.Orientation) orb.Geometry {
 }
 
 // Ring will smart clip a ring to the boundary. This may result multiple rings so
-// a multipolygon is possible.
+// a multipolygon is possible. Rings that are NOT closed AND have an endpoint in
+// the bound will be implicitly closed.
 func Ring(box orb.Bound, r orb.Ring, o orb.Orientation) orb.MultiPolygon {
 	if len(r) == 0 {
 		return nil
@@ -82,6 +84,8 @@ func Ring(box orb.Bound, r orb.Ring, o orb.Orientation) orb.MultiPolygon {
 }
 
 // Polygon will smart clip a polygon to the bound.
+// Rings that are NOT closed AND have an endpoint in the bound will be
+// implicitly closed.
 func Polygon(box orb.Bound, p orb.Polygon, o orb.Orientation) orb.MultiPolygon {
 	if len(p) == 0 {
 		return nil
@@ -110,6 +114,8 @@ func Polygon(box orb.Bound, p orb.Polygon, o orb.Orientation) orb.MultiPolygon {
 }
 
 // MultiPolygon will smart clip a multipolygon to the bound.
+// Rings that are NOT closed AND have an endpoint in the bound will be
+// implicitly closed.
 func MultiPolygon(box orb.Bound, mp orb.MultiPolygon, o orb.Orientation) orb.MultiPolygon {
 	if len(mp) == 0 {
 		return nil
@@ -160,6 +166,9 @@ func MultiPolygon(box orb.Bound, mp orb.MultiPolygon, o orb.Orientation) orb.Mul
 func clipRings(box orb.Bound, rings []orb.Ring) (open []orb.LineString, closed []orb.Ring) {
 	var result []orb.LineString
 	for _, r := range rings {
+		if !r.Closed() && (box.Contains(r[0]) || box.Contains(r[len(r)-1])) {
+			r = append(r, r[0])
+		}
 		out := clip.LineString(box, orb.LineString(r), clip.OpenBound(true))
 		if len(out) == 0 {
 			continue // outside of bound
@@ -277,7 +286,7 @@ func smartWrap(box orb.Bound, input []orb.LineString, o orb.Orientation) orb.Mul
 	)
 
 	// this operation is O(n^2). Technically we could use a linked list
-	// and remove poitns instead of marking them as "used".
+	// and remove points instead of marking them as "used".
 	// However since n is 2x the number of segements I think we're okay.
 	for i := 0; i < 2*len(points); i++ {
 		ep := points[i%len(points)]

clip/smartclip/smart_test.go

@@ -35,6 +35,24 @@ func TestRing(t *testing.T) {
 			input:    orb.Ring{{2, 2}, {3, 2}, {3, 3}, {2, 3}, {2, 2}},
 			expected: orb.MultiPolygon{{{{2, 2}, {3, 2}, {3, 3}, {2, 3}, {2, 2}}}},
 		},
+		{
+			name:     "not closed with endpoints inside bound",
+			bound:    oneSix,
+			input:    orb.Ring{{2, 2}, {8, 2}, {8, 3}, {2, 3}},
+			expected: orb.MultiPolygon{{{{2, 2}, {6, 2}, {6, 3}, {2, 3}, {2, 2}}}},
+		},
+		{
+			name:     "not closed with first endpoint inside bound",
+			bound:    oneSix,
+			input:    orb.Ring{{2, 2}, {8, 2}, {8, 3}, {0, 3}},
+			expected: orb.MultiPolygon{{{{6, 3}, {1, 3}, {1, 2.5}, {2, 2}, {6, 2}, {6, 3}}}},
+		},
+		{
+			name:     "not closed with last endpoint inside bound",
+			bound:    oneSix,
+			input:    orb.Ring{{0, 2}, {8, 2}, {8, 3}, {2, 3}},
+			expected: orb.MultiPolygon{{{{6, 3}, {2, 3}, {1, 2.5}, {1, 2}, {6, 2}, {6, 3}}}},
+		},
 		{
 			name:     "intersects one side",
 			bound:    oneSix,