def __init__(self, transform_pix2angle, ra_at_xy_0, dec_at_xy_0):
        """
        initialize the coordinate-to-pixel transform and their inverse
        :param transform_pix2angle: 2x2 matrix, mapping of pixel to coordinate
        :param ra_at_xy_0: ra coordinate at pixel (0,0)
        :param dec_at_xy_0: dec coordinate at pixel (0,0)
        """
        self._Mpix2a = transform_pix2angle
        self._Ma2pix = linalg.inv(self._Mpix2a)
        self._ra_at_xy_0 = ra_at_xy_0
        self._dec_at_xy_0 = dec_at_xy_0
        self._x_at_radec_0, self._y_at_radec_0 = util.map_coord2pix(-self._ra_at_xy_0, -self._dec_at_xy_0, 0, 0, self._Ma2pix)
def __init__ ( self , transform_pix2angle , ra_at_xy_0 , dec_at_xy_0 ) : self . _Mpix2a = transform_pix2angle self . _Ma2pix = linalg . inv ( self . _Mpix2a ) self . _ra_at_xy_0 = ra_at_xy_0 self . _dec_at_xy_0 = dec_at_xy_0 self . _x_at_radec_0 , self . _y_at_radec_0 = util . map_coord2pix ( - self . _ra_at_xy_0 , - self . _dec_at_xy_0 , 0 , 0 , self . _Ma2pix )
initialize the coordinate-to-pixel transform and their inverse
        :param transform_pix2angle: 2x2 matrix, mapping of pixel to coordinate
        :param ra_at_xy_0: ra coordinate at pixel (0,0)
        :param dec_at_xy_0: dec coordinate at pixel (0,0)