// 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(g *geos.Geos, rel *element.Relation, rings []*ring) (*geos.Geom, error) {
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
rings[i].outer = false
} else {
shells[rings[j]] = true
rings[i].outer = true
}
}
}
if rings[i].containedBy == -1 {
// add as shell if it is not a hole
shells[rings[i]] = true
rings[i].outer = true
}
g.PreparedDestroy(testGeom)
}
var polygons []*geos.Geom
for shell, _ := range shells {
var interiors []*geos.Geom
for hole, _ := range shell.holes {
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)
}
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.")
}
}
var err error
result, err = g.MakeValid(result)
if err != nil {
return nil, err
}
g.DestroyLater(result)
outer := make(map[int64]struct{})
for i := range rings {
if rings[i].outer {
for _, w := range rings[i].ways {
outer[w.Id] = struct{}{}
}
}
}
for i := range rel.Members {
mid := rel.Members[i].Id
if _, ok := outer[mid]; ok {
rel.Members[i].Role = "outer"
} else {
rel.Members[i].Role = "inner"
}
}
return result, nil
}