Merge pull request #789 from metaxasa/fix-linestring-mvt

Fix LineString feature encoding to use all points and add tests for validation

Author: tidwall

internal/server/mvt.go

@@ -58,13 +58,14 @@ func mvtAddFeature(l *mvt.Layer, tileX, tileY, tileZ int, o mvtObj) {
 		f = l.AddFeature(mvt.LineString)
 		line := g.Base()
 		npoints := line.NumPoints()
-		if npoints > 0 {
-			p := line.PointAt(0)
-			f.MoveTo(mvt.LatLonXY(p.Y, p.X, tileX, tileY, tileZ))
-			for i := 1; i < npoints; i++ {
-				p := line.PointAt(0)
-				f.LineTo(mvt.LatLonXY(p.Y, p.X, tileX, tileY, tileZ))
-			}
+		if npoints < 2 {
+			return
+		}
+		p := line.PointAt(0)
+		f.MoveTo(mvt.LatLonXY(p.Y, p.X, tileX, tileY, tileZ))
+		for i := 1; i < npoints; i++ {
+			p := line.PointAt(i)
+			f.LineTo(mvt.LatLonXY(p.Y, p.X, tileX, tileY, tileZ))
 		}
 		f.AddTag("type", "linestring")
 	case *geojson.Rect:

internal/server/mvt_test.go

@@ -0,0 +1,80 @@
+package server
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/tidwall/geojson"
+	"github.com/tidwall/geojson/geometry"
+	"github.com/tidwall/mvt"
+)
+
+func ls(points []geometry.Point) *geojson.LineString {
+	return geojson.NewLineString(geometry.NewLine(points, nil))
+}
+
+// Ensure that LineString features are encoded using
+// all points in the geometry, not just the first one.
+func TestMVTAddFeatureLineStringUsesAllPoints(t *testing.T) {
+	tileX, tileY, tileZ := 0, 0, 0
+
+	line := ls([]geometry.Point{
+		{X: 1, Y: 1},
+		{X: 2, Y: 2},
+		{X: 3, Y: 3},
+	})
+	id := "line"
+
+	actual := mvtRender(tileX, tileY, tileZ, []mvtObj{{id: id, obj: line}})
+
+	var tile mvt.Tile
+	layer := tile.AddLayer("tile38")
+	layer.SetExtent(4096)
+
+	f := layer.AddFeature(mvt.LineString)
+	series := line.Base()
+	npoints := series.NumPoints()
+	if npoints < 2 {
+		t.Fatalf("expected at least two points, got %d", npoints)
+	}
+	p := series.PointAt(0)
+	x, y := mvt.LatLonXY(p.Y, p.X, tileX, tileY, tileZ)
+	f.MoveTo(x, y)
+	for i := 1; i < npoints; i++ {
+		p = series.PointAt(i)
+		x, y = mvt.LatLonXY(p.Y, p.X, tileX, tileY, tileZ)
+		f.LineTo(x, y)
+	}
+	f.AddTag("type", "linestring")
+	f.AddTag("id", id)
+
+	expected := tile.Render()
+
+	if !bytes.Equal(actual, expected) {
+		t.Fatalf("mvtAddFeature LineString encoding mismatch")
+	}
+}
+
+// LineStrings with fewer than two points should not
+// produce any geometry commands.
+func TestMVTAddFeatureLineStringTooShort(t *testing.T) {
+	tileX, tileY, tileZ := 0, 0, 0
+
+	line := ls([]geometry.Point{
+		{X: 1, Y: 1},
+	})
+
+	actual := mvtRender(tileX, tileY, tileZ, []mvtObj{{id: "short", obj: line}})
+
+	var tile mvt.Tile
+	layer := tile.AddLayer("tile38")
+	layer.SetExtent(4096)
+	_ = layer.AddFeature(mvt.LineString)
+
+	expected := tile.Render()
+
+	if !bytes.Equal(actual, expected) {
+		t.Fatalf("mvtAddFeature LineString with <2 points should not encode geometry")
+	}
+}
+