function save_3dmouthgt( gt_file, gt_m );

  fid = fopen( gt_file, 'wt' );
  if fid < 0
    error( [ mfilename ' could not write-open "' gt_file '"' ] );
  else
    fprintf( fid,'%10.4f %4d %15.8f %15.8f %15.8f\n',gt_m.');
    fclose( fid );
  end