The transformation is made in the geocentric domain using the geocentric translations method (code 9603). However the translation parameter values are derived by bilinear interpolation in a gridded data set. The arguments in accessing the grid are geodetic latitude and longitude of the forward transformation source coordinate reference system. ¶¶The method is reversible.  Iteration for latitude and longitude is required to obtain the correct geocentric translation values. The geocentric translations are applied with sign reversal.