Type of the image: LOLA or WAC

        Note: Specify the attribute ``grid``, ``img`` and ``lbl`

def _category(self):
        """ Type of the image: LOLA or WAC

        Note: Specify the attribute ``grid``, ``img`` and ``lbl`
        """

        if self.fname.split('_')[0] == 'WAC':
            self.grid = 'WAC'
            self.img = os.path.join(self.wacpath, self.fname + '.IMG')
            self.lbl = ''
        elif self.fname.split('_')[0] == 'LDEM':
            self.grid = 'LOLA'
            self.img = os.path.join(self.lolapath, self.fname + '.IMG')
            self.lbl = os.path.join(self.lolapath, self.fname + '.LBL')
        else:
            raise ValueError("%s : This type of image is not recognized. Possible\
                             images are from %s only" % (self.fname, ', '.join(('WAC', 'LOLA'))))