code: func RadialGeoIndexMap(path *geo.Path, meters float64) (*geo.Path, []int) {
  	return radialCore(path, meters, geoDistance, true)
  }
docs: // RadialGeoIndexMap is similar to RadialGeo but returns an array that maps
  // each new path index to its original path index.
  // Returns a new path and DOES NOT modify the original.