private void writeLonLatBounds() {
        writeIfSet("lo1", gds.getLo1());  // longitude of first grid point
        writeIfSet("la1", gds.getLa1());  // latitude of first grid point
        writeIfSet("lo2", gds.getLo2());  // longitude of last grid point
        writeIfSet("la2", gds.getLa2());  // latitude of last grid point