topojson

.travis.yml

@@ -6,6 +6,7 @@ go:
   - 'tip'
 
 install:
+  - go get -v github.com/cheekybits/is
   - go get -v github.com/paulmach/orb/...
   - go install -v
   - go test -i ./...

encoding/topojson/README.md

@@ -0,0 +1,4 @@
+# topojson - TopoJSON implementation in Go
+
+Implements the TopoJSON specification:
+https://github.com/mbostock/topojson-specification

encoding/topojson/bounds.go

@@ -0,0 +1,96 @@
+package topojson
+
+import (
+	"math"
+
+	"github.com/paulmach/orb"
+)
+
+func (t *Topology) bounds() {
+	t.BBox = []float64{
+		math.MaxFloat64,
+		math.MaxFloat64,
+		-math.MaxFloat64,
+		-math.MaxFloat64,
+	}
+
+	for _, f := range t.input {
+		t.boundGeometry(f.Geometry)
+	}
+
+}
+
+func (t *Topology) boundGeometry(g orb.Geometry) {
+	switch c := g.(type) {
+	case orb.Point:
+		t.Bound(c.Bound())
+	case orb.MultiPoint:
+		t.Bound(c.Bound())
+	case orb.LineString:
+		t.Bound(c.Bound())
+	case orb.MultiLineString:
+		t.Bound(c.Bound())
+	case orb.Polygon:
+		t.Bound(c.Bound())
+	case orb.MultiPolygon:
+		t.Bound(c.Bound())
+	case orb.Collection:
+		t.Bound(c.Bound())
+		// for _, geo := range c {
+		// 	t.boundGeometry(geo)
+		// }
+	}
+}
+
+func (t *Topology) Bound(b orb.Bound) {
+	xx := []float64{b.Min[0], b.Max[0]}
+	yy := []float64{b.Min[1], b.Max[1]}
+	for _, x := range xx {
+		if x < t.BBox[0] {
+			t.BBox[0] = x
+		}
+		if x > t.BBox[2] {
+			t.BBox[2] = x
+		}
+	}
+	for _, y := range yy {
+		if y < t.BBox[1] {
+			t.BBox[1] = y
+		}
+		if y > t.BBox[3] {
+			t.BBox[3] = y
+		}
+	}
+}
+
+func (t *Topology) boundPoint(p []float64) {
+	x := p[0]
+	y := p[1]
+
+	if x < t.BBox[0] {
+		t.BBox[0] = x
+	}
+	if x > t.BBox[2] {
+		t.BBox[2] = x
+	}
+	if y < t.BBox[1] {
+		t.BBox[1] = y
+	}
+	if y > t.BBox[3] {
+		t.BBox[3] = y
+	}
+}
+
+func (t *Topology) boundPoints(l [][]float64) {
+	for _, p := range l {
+		t.boundPoint(p)
+	}
+}
+
+func (t *Topology) boundMultiPoints(ml [][][]float64) {
+	for _, l := range ml {
+		for _, p := range l {
+			t.boundPoint(p)
+		}
+	}
+}

encoding/topojson/bounds_test.go

@@ -0,0 +1,27 @@
+package topojson
+
+import (
+	"testing"
+
+	"github.com/cheekybits/is"
+	orb "github.com/paulmach/orb"
+	geojson "github.com/paulmach/orb/geojson"
+)
+
+func TestBBox(t *testing.T) {
+	is := is.New(t)
+
+	in := []*geojson.Feature{
+		NewTestFeature("foo", orb.LineString{
+			orb.Point{0, 0}, orb.Point{1, 0}, orb.Point{2, 0},
+		}),
+		NewTestFeature("bar", orb.LineString{
+			orb.Point{-1, 0}, orb.Point{1, 0}, orb.Point{-2, 3},
+		}),
+	}
+
+	topo := &Topology{input: in}
+	topo.bounds()
+
+	is.Equal(topo.BBox, []float64{-2, 0, 2, 3})
+}

encoding/topojson/cut.go

@@ -0,0 +1,59 @@
+package topojson
+
+func (t *Topology) cut() {
+	junctions := t.join()
+
+	for _, line := range t.lines {
+		mid := line.Start
+		end := line.End
+
+		mid += 1
+		for mid < end {
+			if junctions.Has(t.coordinates[mid]) {
+				next := &arc{Start: mid, End: line.End}
+				line.End = mid
+				line.Next = next
+				line = next
+			}
+			mid += 1
+		}
+	}
+
+	for _, ring := range t.rings {
+		start := ring.Start
+		mid := start
+		end := ring.End
+		fixed := junctions.Has(t.coordinates[start])
+
+		mid += 1
+		for mid < end {
+			if junctions.Has(t.coordinates[mid]) {
+				if fixed {
+					next := &arc{Start: mid, End: ring.End}
+					ring.End = mid
+					ring.Next = next
+					ring = next
+				} else {
+					// For the first junction, we can rotate rather than cut
+					t.rotateCoordinates(start, end, end-mid)
+					t.coordinates[end] = t.coordinates[start]
+					fixed = true
+					mid = start // restart; we may have skipped junctions
+				}
+			}
+			mid += 1
+		}
+	}
+}
+
+func (t *Topology) rotateCoordinates(start, end, offset int) {
+	t.reverseCoordinates(start, end)
+	t.reverseCoordinates(start, start+offset)
+	t.reverseCoordinates(start+offset, end)
+}
+
+func (t *Topology) reverseCoordinates(start, end int) {
+	for i, j := start, end; i < j; i, j = i+1, j-1 {
+		t.coordinates[i], t.coordinates[j] = t.coordinates[j], t.coordinates[i]
+	}
+}