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package orb
// Ring represents a set of ring on the earth.
type Ring LineString
// GeoJSONType returns the GeoJSON type for the object.
func (r Ring) GeoJSONType() string {
return "Polygon"
}
// Dimensions returns 2 because a Ring is a 2d object.
func (r Ring) Dimensions() int {
return 2
}
// Closed will return true if the ring is a real ring.
// ie. 4+ points and the first and last points match.
// NOTE: this will not check for self-intersection.
func (r Ring) Closed() bool {
return (len(r) >= 4) && (r[0] == r[len(r)-1])
}
// Reverse changes the direction of the ring.
// This is done inplace, ie. it modifies the original data.
func (r Ring) Reverse() {
LineString(r).Reverse()
}
// Bound returns a rect around the ring. Uses rectangular coordinates.
func (r Ring) Bound() Bound {
return MultiPoint(r).Bound()
}
// Orientation returns 1 if the the ring is in couter-clockwise order,
// return -1 if the ring is the clockwise order and 0 if the ring is
// degenerate and had no area.
func (r Ring) Orientation() Orientation {
area := 0.0
// This is a fast planar area computation, which is okay for this use.
// implicitly move everything to near the origin to help with roundoff
offsetX := r[0][0]
offsetY := r[0][1]
for i := 1; i < len(r)-1; i++ {
area += (r[i][0]-offsetX)*(r[i+1][1]-offsetY) -
(r[i+1][0]-offsetX)*(r[i][1]-offsetY)
}
if area > 0 {
return CCW
}
if area < 0 {
return CW
}
// degenerate case, no area
return 0
}
// Equal compares two rings. Returns true if lengths are the same
// and all points are Equal.
func (r Ring) Equal(ring Ring) bool {
return MultiPoint(r).Equal(MultiPoint(ring))
}
// Clone returns a new copy of the ring.
func (r Ring) Clone() Ring {
if r == nil {
return nil
}
ps := MultiPoint(r)
return Ring(ps.Clone())
}
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