gis_view_get_location(self->view, &lat, &lon, &elev);
gdouble rg = MAX(0, 1-(elev/20000));
gdouble blue = MAX(0, 1-(elev/50000));
gis_view_get_location(self->view, &lat, &lon, &elev);
gdouble rg = MAX(0, 1-(elev/20000));
gdouble blue = MAX(0, 1-(elev/50000));