🚀 go-pugleaf

Is there a way to tell isosurface to ignore missing or special
values in a 3D grid?  Setting missing values to zero or some
other value does *not* have the desired affect.

The problem of missing values arises all the time in oceanography,
since we are often working with data on some sort of a latitude,
longitude and depth grid, but we only have data in ocean grid cells.
In land grid cells, we have no data, and for graphical techniques 
like contouring and isosurfaces, we want these points to be ignored.  
Most contouring packages (e.g. ISM, NCAR graphics) allow you to define 
a special value, say 1.e35, that indicates to the application that the 
point is to be ignored.  The contouring routine recognized special values,
and no contours are drawn in any box of the grid with a special value at 
one or more of its four corners.   This capability, however, does not
seem to exist in AVS.  Am I missing something fundamental here?

The simple technique of just manipulating the data field by 
setting all the values to zero or some other number does not work,
since contour or isosurface will try to draw contours or isosurfaces between
the "good" data points and the "missing" data points.   I believe the
modules themselves (isosurface, contour to geom ,etc) would have to 
recognize "special values" and act apppropriately to handle this problem.

I would love to here what other people have to say about this problem....

--
Rich Signell               |  rsignell@crusty.er.usgs.gov
U.S. Geological Survey     |  (508) 457-2229  |  FAX (508) 457-2310
Quissett Campus            |  " When marriage is outlawed, 
Woods Hole, MA  02543      |    only outlaws will have inlaws. "