[IDV #MER-177075]: (No Subject)

["Unidata IDV Support" <support-idv@xxxxxxxxxxxxxxxx>]

Hi Donna-

> Attached is a bundle for what I have plotted.  It is for an isosurface of 
> cloud water from the 40 km NAM model.  The problem is that the isosurface 
> contains purple.  But purple is not in the color table used to make the 
> isosurface.  So how do I interpret the purple color in the isosurface?

The issue stems from the way the colors are determined for each triangle that 
makes up the isosurface.  Colors are computed at the vertices of grids, and 
then the colors are interpolated to the places where the iso-surface intersects 
the grid edges
(between pairs of vertices).  In your particular case, the color table has a 
sharp change in color at about the isosurface value so you are getting colors 
from the red and blue ends of the table.  Thus, the purple.   

We see the same thing for radar isosurfaces.  I've sent this off for the VisAD 
people at SSEC to ponder since it's a tricky (and known) issue, but one that 
doesn't have a simple solution.  

In the meantime, a workaround would be to use a color table with out sharp 
color transitions and has fewer colors.

Don 

Ticket Details
===================
Ticket ID: MER-177075
Department: Support IDV
Priority: Normal
Status: Open