// BuildRelGeometry builds the geometry of rel by creating a multipolygon of all rings. // rings need to be sorted by area (large to small). func BuildRelGeometry(rel *element.Relation, rings []*Ring, srid int) (*geos.Geom, error) { g := geos.NewGeos() g.SetHandleSrid(srid) defer g.Finish() totalRings := len(rings) shells := map[*Ring]bool{rings[0]: true} for i := 0; i < totalRings; i++ { testGeom := g.Prepare(rings[i].geom) if testGeom == nil { return nil, errors.New("Error while preparing geometry") } for j := i + 1; j < totalRings; j++ { if g.PreparedContains(testGeom, rings[j].geom) { if rings[j].containedBy != -1 { // j is inside a larger ring, remove that relationship // e.g. j is hole inside a hole (i) delete(rings[rings[j].containedBy].holes, rings[j]) delete(shells, rings[j]) } // remember parent rings[j].containedBy = i // add ring as hole or shell if ringIsHole(rings, j) { rings[i].holes[rings[j]] = true } else { shells[rings[j]] = true } } } if rings[i].containedBy == -1 { // add as shell if it is not a hole shells[rings[i]] = true } g.PreparedDestroy(testGeom) } var polygons []*geos.Geom for shell, _ := range shells { var interiors []*geos.Geom for hole, _ := range shell.holes { hole.MarkInserted(rel.Tags) ring := g.Clone(g.ExteriorRing(hole.geom)) g.Destroy(hole.geom) if ring == nil { return nil, errors.New("Error while getting exterior ring.") } interiors = append(interiors, ring) } shell.MarkInserted(rel.Tags) exterior := g.Clone(g.ExteriorRing(shell.geom)) g.Destroy(shell.geom) if exterior == nil { return nil, errors.New("Error while getting exterior ring.") } polygon := g.Polygon(exterior, interiors) if polygon == nil { return nil, errors.New("Error while building polygon.") } polygons = append(polygons, polygon) } var result *geos.Geom if len(polygons) == 1 { result = polygons[0] } else { result = g.MultiPolygon(polygons) if result == nil { return nil, errors.New("Error while building multi-polygon.") } } if !g.IsValid(result) { buffered := g.Buffer(result, 0) if buffered == nil { return nil, errors.New("Error while fixing geom with buffer(0)") } g.Destroy(result) result = buffered } g.DestroyLater(result) insertedWays := make(map[int64]bool) for _, r := range rings { for id, _ := range r.inserted { insertedWays[id] = true } } wkb := g.AsEwkbHex(result) if wkb == nil { return nil, errors.New("unable to create WKB for relation") } rel.Geom = &element.Geometry{Geom: result, Wkb: wkb} return result, nil }