object new_volume(int smooth_normals, int stop_at_first,
int xres, int yres, int zres,
isosurface_val *field_data, isosurface_val threshold);
A Volume primitive is a cubical array of field values which define a field in a region of space. The threshold surface_val is used to find a 'three-dimensional contour line' or isosurface where the field reaches this value.
The flag smooth determines whether or not the normals are smoothed out or remain patchy. The flag stop behaves as for the heightfield. xres, yres, zres define the resolution