func SplitPolygonAtGrid(g *geos.Geos, geom *geos.Geom, gridWidth, currentGridWidth float64) ([]*geos.Geom, error) {
var result []*geos.Geom
geomBounds := geom.Bounds()
if geomBounds == geos.NilBounds {
return nil, errors.New("couldn't create bounds for geom")
}
for _, bounds := range tileBounds(geom.Bounds(), currentGridWidth) {
clipGeom := g.BoundsPolygon(bounds)
if clipGeom == nil {
return nil, errors.New("couldn't create bounds polygon")
}
part := g.Intersection(geom, clipGeom)
if part == nil {
return nil, errors.New("couldn't create intersection")
}
if !g.IsEmpty(part) && strings.HasSuffix(g.Type(part), "Polygon") {
if gridWidth >= currentGridWidth {
result = append(result, part)
} else {
moreParts, err := SplitPolygonAtGrid(g, part, gridWidth, currentGridWidth/10.0)
if err != nil {
return nil, err
}
result = append(result, moreParts...)
}
}
}
return result, nil
}
func flattenLineStrings(g *geos.Geos, geoms []*geos.Geom) []*geos.Geom {
var result []*geos.Geom
for _, geom := range geoms {
if g.Type(geom) == "MultiLineString" {
for _, part := range g.Geoms(geom) {
result = append(result, g.Clone(part))
}
g.Destroy(geom)
} else if g.Type(geom) == "LineString" {
result = append(result, geom)
} else {
log.Printf("unexpected geometry type in flattenPolygons")
g.Destroy(geom)
}
}
return result
}
func filterGeometryByType(g *geos.Geos, geom *geos.Geom, targetType string) []*geos.Geom {
// Filter (multi)geometry for compatible `geom_type`,
// because we can't insert points into linestring tables for example
geomType := g.Type(geom)
if geomType == targetType {
// same type is fine
return []*geos.Geom{geom}
}
if geomType == "Polygon" && targetType == "MultiPolygon" {
// multipolygon mappings also support polygons
return []*geos.Geom{geom}
}
if geomType == "MultiPolygon" && targetType == "Polygon" {
// polygon mappings should also support multipolygons
return []*geos.Geom{geom}
}
if g.NumGeoms(geom) >= 1 {
// GeometryCollection or MultiLineString? return list of geometries
var geoms []*geos.Geom
for _, part := range g.Geoms(geom) {
// only parts with same type
if g.Type(part) == targetType {
geoms = append(geoms, g.Clone(part))
}
}
g.Destroy(geom)
if len(geoms) != 0 {
return geoms
}
return []*geos.Geom{}
}
g.Destroy(geom)
return []*geos.Geom{}
}