encoding/mvt: skip encoding of features will nil geometry

encoding/mvt/clip.go

@@ -22,9 +22,18 @@ func (ls Layers) Clip(box orb.Bound) {
 }
 
 // Clip will clip all geometries in this layer to the given bounds.
+// Will remove features that clip to an empty geometry, modifies the
+// layer.Features slice in place.
 func (l *Layer) Clip(box orb.Bound) {
+ at := 0
  for _, f := range l.Features {
  g := clip.Geometry(box, f.Geometry)
- f.Geometry = g
+ if g != nil {
+ f.Geometry = g
+ l.Features[at] = f
+ at++
+ }
  }
+
+ l.Features = l.Features[:at]
 }

encoding/mvt/clip_test.go

@@ -1,10 +1,11 @@
 package mvt
 
 import (
- "github.com/paulmach/orb"
- "github.com/paulmach/orb/geojson"
  "reflect"
  "testing"
+
+ "github.com/paulmach/orb"
+ "github.com/paulmach/orb/geojson"
 )
 
 func TestLayersClip(t *testing.T) {
@@ -56,3 +57,24 @@ func TestLayersClip(t *testing.T) {
  })
  }
 }
+
+func TestLayerClip_empty(t *testing.T) {
+ layer := &Layer{
+ Features: []*geojson.Feature{
+ geojson.NewFeature(orb.Polygon{{
+ {-1, 1}, {0, 1}, {1, 1}, {1, 5}, {1, -5},
+ }}),
+ geojson.NewFeature(orb.LineString{{55, 0}, {66, 0}}),
+ },
+ }
+
+ layer.Clip(orb.Bound{Min: orb.Point{50, -10}, Max: orb.Point{70, 10}})
+
+ if v := len(layer.Features); v != 1 {
+ t.Errorf("incorrect number of features: %d", v)
+ }
+
+ if v := layer.Features[0].Geometry.GeoJSONType(); v != "LineString" {
+ t.Errorf("kept the wrong geometry: %v", layer.Features[0].Geometry)
+ }
+}

encoding/mvt/marshal.go

@@ -40,6 +40,7 @@ func MarshalGzipped(layers Layers) ([]byte, error) {
 }
 
 // Marshal will take a set of layers and encode them into a Mapbox Vector Tile format.
+// Features that have a nil geometry, for some reason, will be skipped and not included.
 func Marshal(layers Layers) ([]byte, error) {
  vt := &vectortile.Tile{
  Layers: make([]*vectortile.Tile_Layer, 0, len(layers)),
@@ -73,6 +74,10 @@ func Marshal(layers Layers) ([]byte, error) {
 }
 
 func addFeature(layer *vectortile.Tile_Layer, kve *keyValueEncoder, f *geojson.Feature) error {
+ if f.Geometry == nil {
+ return nil
+ }
+
  if f.Geometry.GeoJSONType() == "GeometryCollection" {
  for _, g := range f.Geometry.(orb.Collection) {
  return addSingleGeometryFeature(layer, kve, g, f.Properties, f.ID)

encoding/mvt/marshal_test.go

@@ -138,6 +138,39 @@ func TestMarshalUnmarshalForGeometryCollection(t *testing.T) {
  }
 }
 
+func TestMarshal_nilGeometry(t *testing.T) {
+ // should handle nil geometry, possibly caused by clipping
+ // or other issues.
+
+ fc := geojson.NewFeatureCollection()
+ fc.Append(geojson.NewFeature(nil))
+
+ layers := Layers{NewLayer("roads", fc)}
+
+ // project to the tile coords
+ tile := maptile.New(0, 0, 15)
+ layers.ProjectToTile(tile)
+
+ // marshal
+ encoded, err := MarshalGzipped(layers)
+ if err != nil {
+ t.Fatalf("marshal error: %v", err)
+ }
+
+ // unmarshal
+ decoded, err := UnmarshalGzipped(encoded)
+ if err != nil {
+ t.Fatalf("unmarshal error: %v", err)
+ }
+
+ // project back
+ decoded.ProjectToWGS84(tile)
+
+ if v := len(decoded[0].Features); v != 0 {
+ t.Errorf("should have have any features, has %v", v)
+ }
+}
+
 func TestMarshalUnmarshal(t *testing.T) {
  cases := []struct {
  name string