Specific alpha values

• To: VisAD List <visad-list@xxxxxxxxxxxxx>
• Subject: Specific alpha values
• From: Andrew Donaldson <A.Donaldson@xxxxxxxxxx>
• Date: Tue, 22 May 2001 17:17:33 +1000

Hi there,

  I've got some radar data in my visad display, which I am overlaying
over a filled in map and some other stuff.  The radar data is from
a McIDAS ADDE image server.

  The bad bit is that a large black box surrounds the small amounts
of rain (radar data).
  So what I want to do is set 0 values in the radar data to be
transparent.
  This is something along the lines of mapping radarValue to ALPHA,
but not quite, as I don't want a linear relationship.. I want to
define my own function (in loose language).  This seems to be
possible with mapping samples to colours, where you get your mouse
and choose the R, G and B intensities for that sample, on a
contiguous sample space thingy.
  Can I do this for alpha?  How do I do it programatically?  I don't
want the user having to drag his mouse around just to set 'no rain'
to be transparent.

thanks in advance,

Andrew.

-- 
 Andrew Donaldson                                           
 Email:   A.Donaldson@xxxxxxxxxx                Bureau of Meteorology
 Phone:   +61 3 9669 4537            P.O. Box. 1289K/150 Lonsdale St,
 Fax:     +61 3 9669 4128                       Melbourne, Australia.

• Follow-Ups:
  • Re: Specific alpha values
    • From: Ugo Taddei
  • Re: Specific alpha values
    • From: Bill Hibbard