func SymmetricDifference(js geojson.GeoJSON) (*geojson.FeatureCollection, error) {
polygons, err := geometryToPolygonList(js)
if err != nil {
return nil, err
}
var features []geojson.Feature
for i := 0; i < len(polygons); i++ {
a := polygons[i]
for j := 0; j < len(polygons); j++ {
if i == j {
continue
}
var c s2.Polygon
b := polygons[j]
c.InitToDifference(a, b)
a = &c
}
if a.NumLoops() > 0 {
feat := geojson.Feature{
Typ: "Feature",
Geometry: s2PolygonToGeometry(*a),
}
features = append(features, feat)
}
}
fc := &geojson.FeatureCollection{
Typ: "FeatureCollection",
Features: features,
}
return fc, nil
}
func Union(js geojson.GeoJSON) (*geojson.FeatureCollection, error) {
polygons, err := geometryToPolygonList(js)
if err != nil {
return nil, err
}
a := polygons[0]
for i := 1; i < len(polygons); i++ {
var c s2.Polygon
b := polygons[i]
c.InitToUnion(a, b)
a = &c
}
return featureCollectionFromS2Polygon(a), nil
}
func s2PolygonToGeometry(poly s2.Polygon) *geojson.Polygon {
// Don't want nil rings for coordinates.
rings := [][]geojson.Coordinate{}
for i := 0; i < poly.NumLoops(); i++ {
loop := poly.Loop(i)
var ring []geojson.Coordinate
for j := 0; j <= loop.NumVertices(); j++ {
ll := s2.LatLngFromPoint(*loop.Vertex(j))
ring = append(ring, geojson.Coordinate{ll.Lng.Degrees(), ll.Lat.Degrees()})
}
rings = append(rings, ring)
}
return &geojson.Polygon{Typ: "Polygon", Coordinates: rings}
}
func Intersection(js geojson.GeoJSON) (*geojson.FeatureCollection, error) {
polygons, err := geometryToPolygonList(js)
if err != nil {
return nil, err
}
var intersections []*s2.Polygon
for i := 0; i < len(polygons); i++ {
a := polygons[i]
for j := i + 1; j < len(polygons); j++ {
var c s2.Polygon
b := polygons[j]
c.InitToIntersection(a, b)
intersections = append(intersections, &c)
}
}
a := intersections[0]
for i := 1; i < len(intersections); i++ {
b := intersections[i]
var c s2.Polygon
c.InitToUnion(a, b)
a = &c
}
return featureCollectionFromS2Polygon(a), nil
}