The main function of interest in plwf.py is the function plwf (``plot wire frame''), which enables the user to plot an arbitrary wire frame on a quadrilateral grid. The grid may be see-through or not (cells filled with the background color). In the latter case, the drawing order of the zones is determined by a simple ``painter's algorithm'', which works fairly well if the mesh is reasonably nearly rectilinear, but can fail even then if the viewpoint is chosen to produce extreme fisheye perspective effects. One must look at the resulting plot carefully to be sure the algorithm has correctly rendered the model in each case.
A 3D wire mesh can also be plotted using shading and lighting effects as determined by values set in the pl3d module; or the zones can be colored (using the current palette) by their average height or by the values of some function, which may be zone-centered or node-centered.