code: func (r VisvalingamReducer) GeoReduce(path *geo.Path) *geo.Path {
  	factor := geo.MercatorScaleFactor(path.Bound().Center().Lat())
  	path.Transform(geo.Mercator.Project)
  
  	reduced := Visvalingam(path, r.Threshold*factor*factor, r.ToKeep)
  	return reduced.Transform(geo.Mercator.Inverse)
  }
docs: // GeoReduce runs the Visvalingam reduction on a lng/lat path.
  // The threshold is expected to be in meters squared.