the longitude and latitude directions (next input line)  are negative, the number of points in the
$     longitude direction (nx) will in fact correspond to the total number of points; the points defining
$     the topography will be assumed to be randomly distributed (not on a rectangular grid);
$     the number of points in the latitude direction (ny) will contain the number of triangles connecting
$     the randomly distributed points.
$     the topography file should then contain nx triplets of longitud