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