  plw3d(basex, basey, height, xmin, xmax, ymin, ymax, zmin, zmax, alt, az)
  ************************************************************************

  plw3d

  Sets up a window for a three-dimensional surface plot within the
  currently defined two-dimensional window. The enclosing box for the surface
  plot defined by xmin, xmax, ymin, ymax, zmin and zmax in user-coordinate
  space is mapped into a box of world coordinate size basex by basey by
  height so that xmin maps to -basex/2, xmax maps to basex/2, ymin maps to
  -basey/2, ymax maps to basey/2, zmin maps to 0 and zmax maps to height. The
  resulting world-coordinate box is then viewed by an observer at altitude
  alt and azimuth az. This routine must be called before plbox3 or plot3d.
  For a more complete description of three-dimensional plotting 3-d Plots.

  basex (PLFLT, input): The x coordinate size of the world-coordinate box.

  basey (PLFLT, input): The y coordinate size of the world-coordinate box.

  height (PLFLT, input): The z coordinate size of the world-coordinate
  box.

  xmin (PLFLT, input): The minimum user x coordinate value.

  xmax (PLFLT, input): The maximum user x coordinate value.

  ymin (PLFLT, input): The minimum user y coordinate value.

  ymax (PLFLT, input): The maximum user y coordinate value.

  zmin (PLFLT, input): The minimum user z coordinate value.

  zmax (PLFLT, input): The maximum user z coordinate value.

  alt (PLFLT, input): The viewing altitude in degrees above the xy plane.

  az (PLFLT, input): The viewing azimuth in degrees. When az=0, the
  observer is looking face onto the zx plane, and as az is increased, the
  observer moves clockwise around the box when viewed from above the xy
  plane.

