docs: def coord_grid(self):
          """Draw a grid of RA/DEC on Canvas."""
  
          ra2 = math.pi * 2
          ra1 = 0
          dec1 = -1 * math.pi / 2.0
          dec2 = math.pi / 2.0
  
          dra = math.fabs((self.x2 - self.x1) / 4.0)
          ddec = math.fabs((self.y2 - self.y1) / 4.0)
          logging.debug("Drawing the grid.")
          label = True
          ra = ra1
          while ra <= ra2:
              # create a line that goes from dec1 to dec2 at this ra
              (cx1, cy1) = self.p2c((ra, dec1))
              # ly is the y location mid-way between the top and bottom of the plot
              (cx2, cy2) = self.p2c((ra, dec2))
              # create a dashed line for un-labeled lines
              self.create_line(cx1, cy1, cx2, cy2, dash=(20, 20), fill="grey")
              dec = dec1
              while dec <= dec2:
                  if label:
                      # lx is the the x screen coordinate location of the ra
                      (lx, ly) = self.p2c((ra, dec + ddec / 2.0))
                      self.create_text(lx + 5, ly, justify=LEFT,
                                       font=('Times', '-20'),
                                       text="\n".join(str(ephem.hours(ra))[:-3]), fill='grey')
                  label = not label
                  dec += ddec
              ra += dra
  
          # plot dec grid lines bewtween South (dec1) and North (dec2) limits of plot
          dec = dec1
          # should we label the current grid line?
          label = True
          while dec <= dec2:
              # create a line the goes from ra1 to ra2 at this dec
              (cx1, cy1) = self.p2c((ra1, dec))
              (cx2, cy2) = self.p2c((ra2, dec))
              self.create_line(cx1, cy1, cx2, cy2, dash=(20, 20), fill='grey')
              ra = ra1
              while ra <= ra2:
                  if label:
                      # lx/ly are the screen coordinates of the label
                      (lx, ly) = self.p2c((ra + dra / 2.0, dec))
                      self.create_text(lx, ly - 5, font=('Times', '-20'),
                                       text=str(ephem.degrees(dec)), fill='grey')
                  ra += dra
              dec += ddec
              label = not label