private void writeRotationAndStretch() {
        writeIfSet("spLon", gds.getSpLon());  // longitude of the southern pole of projection
        writeIfSet("spLat", gds.getSpLat());  // latitude of the southern pole of projection
        writeIfSet("rotationAngle", gds.getRotationAngle());
        writeIfSet("poleLon", gds.getPoleLon());  // longitude of the pole stretching