photoprism/pkg/s2/s2.go

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