[mapserver-users] Mapping a raster colour to Transparent

[Dylan Keon]

Tweedy, Scott wrote:
 > Is there any way to use MapServer to map a specific colour value in an
 > input file to end up being transparent in the output PNG or GIF?

Check out the OFFSITE parameter.  If you have a standard colormap (for a 
DRG, for example), like this:

# value red green blue
0 255 255 255
1 0 0 0
2 255 255 255
3 91 159 230
4 230 45 30
...

give OFFSITE the value of the pixels you want to be transparent, like this:

LAYER
   NAME drg_index
   STATUS ON
   TYPE raster
   OFFSITE 0
   TILEINDEX drg_index
   TILEITEM "location"
   MAXSCALE 50000
   MINSCALE 2000
END

--Dylan

-- 
************************************************
  Dylan Keon
  GIS/Database Research Specialist
  Northwest Alliance for Computational
  Science and Engineering (NACSE)
  Oregon State University
  Corvallis, OR 97331
  keon@nacse.org        (541) 737-6608
************************************************