A question about interpolation

[Brian E. Doty]

The locations where the contour lines intersect
the grid are determined using bi-linear interpolation
between grid points.

If you have "csmooth" set to off, and "cterp" set to
off, you will see just the line segments plotted,
within grid cells.

When "cterp" is set to on, the first step is as
above, to determine where the contour line intersects
the grid.  Then a curve is fitted to these points,
using a modified spline technique (not quite the
formal cubic spline fit; it is modified for
better performance).

When "csmooth" is set to on, the grid to be plotted
is first interpolated to a finer grid, using a
bicubic interpolation technique.  Then this finer
grid is contoured using bi-linear interpolation
(and the spline fit if "cterp" is also on).

The default is for "cterp" to be on, and for
"csmooth" to be off... Brian