80 lines
1.7 KiB
Go
80 lines
1.7 KiB
Go
/*
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Package s2 encapsulates Google's S2 library.
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Additional information can be found in our Developer Guide:
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https://github.com/photoprism/photoprism/wiki
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...and in the Google S2 documentation:
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https://s2geometry.io/
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*/
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package s2
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import (
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gs2 "github.com/golang/geo/s2"
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)
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// Default cell level, see https://s2geometry.io/resources/s2cell_statistics.html.
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var DefaultLevel = 21
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// Token returns the S2 cell token for coordinates using the default level.
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func Token(lat, lng float64) string {
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return TokenLevel(lat, lng, DefaultLevel)
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}
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// Token returns the S2 cell token for coordinates.
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func TokenLevel(lat, lng float64, level int) string {
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if lat == 0.0 && lng == 0.0 {
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return ""
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}
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if lat < -90 || lat > 90 {
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return ""
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}
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if lng < -180 || lng > 180 {
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return ""
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}
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l := gs2.LatLngFromDegrees(lat, lng)
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return gs2.CellIDFromLatLng(l).Parent(level).ToToken()
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}
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// LatLng returns the coordinates for a S2 cell token.
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func LatLng(token string) (lat, lng float64) {
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if token == "" || token == "-" {
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return 0.0, 0.0
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}
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c := gs2.CellIDFromToken(token)
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if !c.IsValid() {
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return 0.0, 0.0
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}
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l := c.LatLng()
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return l.Lat.Degrees(), l.Lng.Degrees()
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}
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// IsZero returns true if the coordinates are both empty.
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func IsZero(lat, lng float64) bool {
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return lat == 0.0 && lng == 0.0
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}
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// Range returns a token range for finding nearby locations.
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func Range(token string, levelUp int) (min, max string) {
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c := gs2.CellIDFromToken(token)
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if !c.IsValid() {
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return min, max
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}
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// See https://s2geometry.io/resources/s2cell_statistics.html
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lvl := c.Level()
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parent := c.Parent(lvl - levelUp)
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return parent.Prev().ChildBeginAtLevel(lvl).ToToken(), parent.Next().ChildBeginAtLevel(lvl).ToToken()
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}
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