Adds constrained delaunay triangulation

geom.go

@@ -128,3 +128,79 @@ func GetCoordinates(g Geometry) (pts []Point, err error) {
 	err = getCoordinates(g, &pts)
 	return pts, err
 }
+
+// extractLines is a helper function for ExtractLines to avoid too many
+// array copies and still provide a convenient interface to the user.
+func extractLines(g Geometry, lines *[]Line) error {
+	switch gg := g.(type) {
+
+	default:
+
+		return ErrUnknownGeometry{g}
+
+	case Pointer:
+
+		return nil
+
+	case MultiPointer:
+
+		return nil
+
+	case LineStringer:
+
+		v := gg.Verticies()
+		for i := 0; i < len(v)-1; i++ {
+			*lines = append(*lines, Line{v[i], v[i+1]})
+		}
+		return nil
+
+	case MultiLineStringer:
+
+		for _, ls := range gg.LineStrings() {
+			if err := extractLines(LineString(ls), lines); err != nil {
+				return err
+			}
+		}
+		return nil
+
+	case Polygoner:
+
+		for _, ls := range gg.LinearRings() {
+			if err := extractLines(LineString(ls), lines); err != nil {
+				return err
+			}
+		}
+		return nil
+
+	case MultiPolygoner:
+
+		for _, p := range gg.Polygons() {
+			if err := extractLines(Polygon(p), lines); err != nil {
+				return err
+			}
+		}
+		return nil
+
+	case Collectioner:
+
+		for _, child := range gg.Geometries() {
+			if err := extractLines(child, lines); err != nil {
+				return err
+			}
+		}
+		return nil
+
+	}
+}
+
+/*
+ExtractLines extracts all linear components from a geometry (line segements).
+If the geometry contains no line segements (e.g. empty geometry or
+point), then an empty array will be returned.
+
+Duplicate lines will not be removed.
+*/
+func ExtractLines(g Geometry) (lines []Line, err error) {
+	err = extractLines(g, &lines)
+	return lines, err
+}

geom_test.go

@@ -24,6 +24,11 @@ func TestGetCoordinates(t *testing.T) {
 		}
 	}
 	testcases := []tcase{
+		{
+			geom:     Extent{},
+			expected: nil,
+			err:      ErrUnknownGeometry{Extent{}},
+		},
 		{
 			geom:     Point{10, 20},
 			expected: []Point{{10, 20}},
@@ -124,3 +129,127 @@ func TestGetCoordinates(t *testing.T) {
 		t.Run(strconv.FormatInt(int64(i), 10), func(t *testing.T) { fn(t, tc) })
 	}
 }
+
+func TestExtractLines(t *testing.T) {
+
+	type tcase struct {
+		geom     Geometry
+		expected []Line
+		err      error
+	}
+
+	fn := func(t *testing.T, tc tcase) {
+		r, err := ExtractLines(tc.geom)
+		if err != tc.err {
+			t.Errorf("error, expected %v got %v", tc.err, err)
+		}
+		if !(len(r) == 0 && len(tc.expected) == 0) && !reflect.DeepEqual(r, tc.expected) {
+			t.Errorf("error, expected %v got %v", tc.expected, r)
+		}
+	}
+	testcases := []tcase{
+		{
+			geom:     Extent{},
+			expected: nil,
+			err:      ErrUnknownGeometry{Extent{}},
+		},
+		{
+			geom:     Point{10, 20},
+			expected: []Line{},
+			err:      nil,
+		},
+		{
+			geom: MultiPoint{
+				{10, 20},
+				{30, 40},
+				{-10, -5},
+			},
+			expected: []Line{},
+			err:      nil,
+		},
+		{
+			geom: LineString{
+				{10, 20},
+				{30, 40},
+				{-10, -5},
+			},
+			expected: []Line{{{10, 20}, {30, 40}}, {{30, 40}, {-10, -5}}},
+			err:      nil,
+		},
+		{
+			geom: MultiLineString{
+				{
+					{10, 20},
+					{30, 40},
+				},
+				{
+					{-10, -5},
+					{15, 20},
+				},
+			},
+			expected: []Line{{{10, 20}, {30, 40}}, {{-10, -5}, {15, 20}}},
+			err:      nil,
+		},
+		{
+			geom: Polygon{
+				{
+					{10, 20},
+					{30, 40},
+					{-10, -5},
+				},
+				{
+					{1, 2},
+					{3, 4},
+				},
+			},
+			expected: []Line{{{10, 20}, {30, 40}}, {{30, 40}, {-10, -5}}, {{1, 2}, {3, 4}}},
+			err:      nil,
+		},
+		{
+			geom: MultiPolygon{
+				{
+					{
+						{10, 20},
+						{30, 40},
+						{-10, -5},
+					},
+					{
+						{1, 2},
+						{3, 4},
+					},
+				},
+				{
+					{
+						{5, 6},
+						{7, 8},
+						{9, 10},
+					},
+				},
+			},
+			expected: []Line{{{10, 20}, {30, 40}}, {{30, 40}, {-10, -5}}, {{1, 2}, {3, 4}}, {{5, 6}, {7, 8}}, {{7, 8}, {9, 10}}},
+			err:      nil,
+		},
+		{
+			geom: Collection{
+				Point{10, 20},
+				MultiPoint{
+					{10, 20},
+					{30, 40},
+					{-10, -5},
+				},
+				LineString{
+					{1, 2},
+					{3, 4},
+					{5, 6},
+				},
+			},
+			expected: []Line{{{1, 2}, {3, 4}}, {{3, 4}, {5, 6}}},
+			err:      nil,
+		},
+	}
+
+	for i, tc := range testcases {
+		tc := tc
+		t.Run(strconv.FormatInt(int64(i), 10), func(t *testing.T) { fn(t, tc) })
+	}
+}

planar/triangulate/README.md

@@ -7,9 +7,10 @@ porting are:
 * Stay true to JTS's implementation, but make the necessary changes to stay 
   go-ish and fit nicely within the geom package.
 * Only implement what is needed as it is needed.
-* When possible, keep modifications to the functionality segregated into 
+* When reasonable, keep modifications to the functionality segregated into 
   different directories. This will help minimize the cost of porting more of 
-  JTS's functionality or porting JTS's future changes.
+  JTS's functionality or porting JTS's future changes. When it isn't 
+  reasonable, make a specific note of the difference in the comments.
 
 To make porting easier, the original Java code will be kept in the source 
 files until the specific function has been ported at which time the Java 

planar/triangulate/constraineddelaunay/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2017 go-spatial
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

planar/triangulate/constraineddelaunay/README.md

@@ -0,0 +1,12 @@
+
+
+This constrained delaunay triangulation implementation is based on:
+
+Domiter, Vid. "Constrained Delaunay triangulation using plane subdivision." 
+Proceedings of the 8th central European seminar on computer graphics. 
+Budmerice. 2004.
+http://old.cescg.org/CESCG-2004/web/Domiter-Vid/CDT.pdf
+
+While this code makes heavy use of the JTS port, it is all new code. As such 
+it can fall under the MIT license.
+