Proof of Concept Gradient Coloring and Dev question
bill at BINKO.NET
Tue Apr 5 10:35:37 EDT 2005
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
Download the patch (gradient.patch.gz) and save it in your (virgin)
mapserver-4.4.1 source directory.
$ zcat gradient.patch.gz | patch
$ make clean all
install as you normally do (in my case, I just copy the mapserv to my
Then you can add several new elements to your mapfiles:
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 :-)
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.
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