photoprism/pkg/s2/range.go

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package s2
import gs2 "github.com/golang/geo/s2"
// Range returns a token range to find nearby cells within the specified S2 level.
func Range(token string, level int) (start, end string) {
token = NormalizeToken(token)
cell := gs2.CellIDFromToken(token)
if !cell.IsValid() {
return start, end
}
// See https://s2geometry.io/resources/s2cell_statistics.html
cellLevel := cell.Level()
// Range level must not be greater than the cell level.
if level > cellLevel {
level = cellLevel
}
// Get parent cell ID for the given level.
parentCell := cell.Parent(level)
// Return computed S2 cell token range.
return parentCell.Prev().ChildBeginAtLevel(cellLevel).ToToken(), parentCell.Next().ChildBeginAtLevel(cellLevel).ToToken()
}
// PrefixedRange returns a prefixed token range to find nearby cells within the specified S2 level.
func PrefixedRange(token string, level int) (start, end string) {
start, end = Range(token, level)
return Prefix(start), Prefix(end)
}