code: def within_radius(self, viewer, points, pt, canvas_radius):
          
          scales = viewer.get_scale_xy()
          return self.point_within_radius(points, pt, canvas_radius,
                                          scales)
docs: Points `points` and point `pt` are in data coordinates.
          Return True for points within the circle defined by
          a center at point `pt` and within canvas_radius.
          The distance between points is scaled by the canvas scale.