80 lines
1.4 KiB
Go
80 lines
1.4 KiB
Go
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package tz
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import (
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"math"
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)
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type polygon []Point
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func newPoint(lon, lat *float64) *Point {
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return &Point{*lon, *lat}
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}
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func (p polygon) centroid() Point {
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x := 0.0
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y := 0.0
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numPoints := float64(len(p))
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for _, p := range p {
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x += p.Lon
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y += p.Lat
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}
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return Point{x / numPoints, y / numPoints}
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}
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func (p polygon) isClosed() bool {
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if len(p) < 3 {
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return false
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}
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return true
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}
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// Returns whether or not the current Polygon contains the passed in Point.
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func (p polygon) contains(point *Point) bool {
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if !p.isClosed() {
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return false
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}
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start := len(p) - 1
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end := 0
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contains := intersectsWithRaycast(point, &p[start], &p[end])
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for i := 1; i < len(p); i++ {
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if intersectsWithRaycast(point, &p[i-1], &p[i]) {
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contains = !contains
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}
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}
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return contains
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}
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// https://rosettacode.org/wiki/Ray-casting_algorithm#Go
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func intersectsWithRaycast(point, start, end *Point) bool {
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if start.Lat > end.Lat {
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start, end = end, start
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}
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for point.Lat == start.Lat || point.Lat == end.Lat {
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point.Lat = math.Nextafter(point.Lat, math.Inf(1))
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}
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if point.Lat < start.Lat || point.Lat > end.Lat {
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return false
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}
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if start.Lon > end.Lon {
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if point.Lon > start.Lon {
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return false
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}
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if point.Lon < end.Lon {
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return true
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}
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} else {
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if point.Lon > end.Lon {
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return false
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}
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if point.Lon < start.Lon {
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return true
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}
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}
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return (point.Lat-start.Lat)/(point.Lon-start.Lon) >= (end.Lat-start.Lat)/(end.Lon-start.Lon)
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}
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