Proof of Concept Gradient Coloring and Dev question

[Bill Binko]

On Tue, 5 Apr 2005, Gerry Creager N5JXS wrote:

> I've gotta go back and look at the archives; I missed this on the first
> pass.  I've got the "lots of classes" solution when plotting
> precipitable water vapor and it's really messy.
>
> Do you have simple tutorial on what you're doing I could snag?  Please?!
>
> Thanks, Gerry

I tried to keep it simple, so here's a quick run-down.  Please remember,
this is not gospel and may be dropped/rewritten -- I've gotten no feedback
from Stephen Lime or others yet.

If you want to try this out and your using linux/unix/bsd/etc., go to the
bug at:

http://mapserver.gis.umn.edu/bugs/show_bug.cgi?id=1305

Download the patch (gradient.patch.gz) and save it in your (virgin)
mapserver-4.4.1 source directory.

run:

$ zcat gradient.patch.gz | patch
$ make clean all

install as you normally do (in my case, I just copy the mapserv to my
cgi-bin directory).

Then you can add several new elements to your mapfiles:

STYLE
  GRADIENTITEM "fieldName" #Must be numeric (float/int)
  MINVALUE 0.0             #The low end of the data values
  MAXVALUE 100.0           #The hight end of the data values
  MINCOLOR 255 0 0         #A color to match low values
  MAXCOLOR 0 255 0         #A color to match high values
  COLOR 0 0 0              #A dummy color - some parts of the
                           #code won't draw without this
                           # - I'll fix it later :-)
END

If your value is lower than MINVALUE, it will get the MINCOLOR (likewise
for MAX).  Values between MIN and MAX will get mapped (linearly) between
the MINCOLOR and MAXCOLOR.

I find that using the Gimp to make some simple linear gradients helps me
pick good colors.

I'll add INCREMENT in the not too distant future and update the patch.

Bill