
  contour <buffer> (overlay) level [Npix]

  "contour" makes a contour plot from the given <buffer> at the
specified level.  If Npix is specified, the image is rebinned by a
factor of Npix in each direction.  The contour is drawn as a series of
lines on the specified overlay.  The new lines are added to any
existing shapes.  (Use "erase" first to erase all objects if desired).

Valid overlays may be: 0, red, 1, green, 2, blue, 3, yellow.

  See also: load, save, erase

