Example #1
0
// 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
}