code: def calc_radius_xy(self, x, y, radius_deg):
          
          # calculate ra/dec of x,y pixel
          ra_deg, dec_deg = self.pixtoradec(x, y)
  
          # Calculate position 1 degree from the given one
          # NOTE: this needs to add in DEC, not RA
          ra2_deg, dec2_deg = wcs.add_offset_radec(ra_deg, dec_deg,
                                                   0.0, 1.0)
  
          # Calculate the length of this segment--it is pixels/deg
          x2, y2 = self.radectopix(ra2_deg, dec2_deg)
          px_per_deg_e = math.sqrt(math.fabs(x2 - x)**2 + math.fabs(y2 - y)**2)
  
          # calculate radius based on desired radius_deg
          radius_px = px_per_deg_e * radius_deg
          return radius_px
docs: Calculate a radius (in pixels) from the point (x, y) to a circle
          defined by radius in degrees.