Vector indicating the geographic zone on which we want to cut the map.
If BOXZOOM has :
1 element : The extraction is made on [lon1, lon2, lat1, lat2, 0.,boxzoom[0]]
2 elements: The extraction is made on [lon1, lon2, lat1, lat2, boxzoom[0],boxzoom[1]]
4 elements: The extraction is made on [Boxzoom, 0, max([gdept, gdepw])]
5 elements: The extraction is made on [Boxzoom[0:3], 0, Boxzoom[4]]
6 elements: The extraction is made on Boxzoom
Where lon1, lon2,lat1,lat2 are global variables defined at the last domdef!