|To obtain a perspective view, you must specify the position (viewpoint)
of the observer. The viewpoint must be outside the workbox. If it is very
close, there will be a lot of perspective distortion. If it is far off,
will be eliminated. The plot will not shrink as the distance of the
viewpoint is increased unless sclfix()
has been called. The viewpoint should be above the x-y plane or
the labels will be backwards. Do not use with vuangl()
or vuabs(). One corner of the x-y
plane must be the closest point to the viewpoint.
To view the surface from below, negate the values produced by zfun(),
or the values loaded in zmat, and view the
surface from above. Be sure that your call to graf3d()
reflects the negated data values.