[EXP] Multilinestring simplification experiments

internal/xy/topo.go

@@ -0,0 +1,75 @@
+package xy
+
+import "fmt"
+
+func RemoveIndex(s []int, index int) []int {
+	return append(s[:index], s[index+1:]...)
+}
+
+type Segment [2]Point
+
+func TopoSimplify(lines [][]Point) [][]Point {
+	sharedPoints := map[Point]int{}
+	segs := map[Segment]bool{}
+	for _, line := range lines {
+		sharedPoints[line[0]] += 2
+		sharedPoints[line[len(line)-1]] += 2
+		for i := 1; i < len(line); i++ {
+			sharedPoints[line[i]] += 1
+			segs[Segment{line[i-1], line[i]}] = true
+		}
+	}
+	fmt.Println("shared points:", sharedPoints)
+	lineSegs := [][]Segment{}
+	for pt, v := range sharedPoints {
+		delete(sharedPoints, pt)
+		if v < 2 {
+			continue
+		}
+		fmt.Println("processing point:", pt)
+		lineSeg := []Segment{}
+		// get open seg
+		for {
+			found := false
+			nseg := Segment{}
+			for nseg = range segs {
+				if nseg[0] == pt {
+					// ok
+					delete(segs, nseg)
+					found = true
+					break
+				}
+				// if nseg[1] == pt {
+				// 	// ok
+				// 	delete(segs, nseg)
+				// 	nseg = Segment{nseg[1], nseg[0]}
+				// 	found = true
+				// 	break
+				// }
+			}
+			if !found {
+				fmt.Println("\t\tno seg for pt:", pt)
+				lineSegs = append(lineSegs, lineSeg)
+				lineSeg = nil
+				break
+			}
+			lineSeg = append(lineSeg, nseg)
+			pt = nseg[1]
+			fmt.Println("\t\tfound:", found, "nseg:", nseg)
+			fmt.Println("\t\tnow:", lineSeg)
+		}
+	}
+	ret := [][]Point{}
+	for _, lineSeg := range lineSegs {
+		rl := []Point{lineSeg[0][0], lineSeg[0][1]}
+		for i := 1; i < len(lineSeg); i++ {
+			rl = append(rl, lineSeg[i][1])
+		}
+		ret = append(ret, rl)
+	}
+	fmt.Println("result:")
+	for _, line := range ret {
+		fmt.Println(line)
+	}
+	return ret
+}

internal/xy/topo_test.go

@@ -0,0 +1,87 @@
+package xy
+
+import (
+	"io/ioutil"
+	"testing"
+
+	geom "github.com/twpayne/go-geom"
+	"github.com/twpayne/go-geom/encoding/geojson"
+)
+
+func TestTopoSimplify(t *testing.T) {
+	testcases := []struct {
+		name string
+		line [][]Point
+	}{
+		{
+			"a",
+			[][]Point{
+				{{0, 1}, {0, 2}, {0, 3}},
+				{{0, 1}, {0, 2}, {0, 3}},
+			},
+		},
+		{
+			"b",
+			[][]Point{
+				{{0, 1}, {0, 4}, {0, 2}, {0, 3}},
+				{{0, 1}, {0, 2}, {0, 3}},
+			},
+		},
+		{
+			"c",
+			[][]Point{
+				{{0, 1}, {0, 1}, {0, 1}, {0, 1}},
+				{{0, 1}, {0, 2}, {0, 3}},
+			},
+		},
+		{
+			"d",
+			[][]Point{
+				{{1, 1}, {1, 2}, {1, 3}},
+				{{0, 1}, {0, 2}, {0, 3}},
+			},
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.name, func(t *testing.T) {
+			TopoSimplify(tc.line)
+		})
+	}
+}
+
+func TestTopoSimplify_File(t *testing.T) {
+	testcases := []struct {
+		name string
+		fn   string
+	}{
+		{
+			"a",
+			"../../test/data/geojson/mls.geojson",
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.name, func(t *testing.T) {
+			data, err := ioutil.ReadFile(tc.fn)
+			if err != nil {
+				t.Fatal(err)
+			}
+			fc := geojson.FeatureCollection{}
+			if err := fc.UnmarshalJSON(data); err != nil {
+				t.Fatal(err)
+			}
+			g, ok := fc.Features[0].Geometry.(*geom.MultiLineString)
+			if !ok {
+				return
+			}
+			var lines [][]Point
+			for i := 0; i < g.NumLineStrings(); i++ {
+				var line []Point
+				for _, c := range g.LineString(i).Coords() {
+					line = append(line, Point{c.X(), c.Y()})
+				}
+				lines = append(lines, line)
+			}
+			TopoSimplify(lines)
+		})
+	}
+}