code: def getRaDecRanges(self, numLines):
          
          x1, x2, y1, y2 = mp.axis()
  
          ra0, dec0 = self.pixToSky(x1, y1)
          ra1, dec1 = self.pixToSky(x2, y2)
  
          #Deal with the case where ra range straddles 0.
          #Different code for case where ra increases left to right, or decreases.
          if self.isPositiveMap():
              if ra1 < ra0:
                  ra1 += 360
          else:
              if ra0 < ra1:
                  ra0 += 360
  
          raMid = .5*(ra0+ra1)
          decMid = .5*(dec0+dec1)
  
  
          xNum, yNum = numLines
          stepX = round((ra1 - ra0) / xNum)
          stepY = round((dec1 - dec0) / yNum)
  
          rangeX = stepX * (xNum - 1)
          rangeY = stepY * (yNum - 1)
  
          raStart = np.round(raMid - rangeX/2.)
          decStart = np.round(decMid - rangeY/2.)
  
          raRange = np.arange(raStart, raStart + stepX*xNum, stepX)
          decRange = np.arange(decStart, decStart + stepY*yNum, stepY)
          raRange = np.fmod(raRange, 360.)
  
          return raRange, decRange
docs: Pick suitable values for ra and dec ticks
  
          Used by plotGrid and labelAxes