Re: [Geotools-gt2-users] ColorMap on polygons

[Ian T. <ijt...@gm...>]

On Fri, May 21, 2010 at 6:12 AM, Andrea Aime <aa...@op...> wrote:
> Michael Bedward ha scritto:
>> Hello,
>>
>>> I'd like to fill the polygons with multiple colors such that adjacent
>>> polygons don't have the same color. How can I do this ?
>>
>> Easiest answer - if number of polygons is small make them all
>> different colors :)
>>
>> General answer...
>> Theoretically you only need four colors to achieve what you want with any map...
>>
>> http://en.wikipedia.org/wiki/Four_color_theorem
>>
>> But it's actually better to have five colors because there is a much
>> faster algorithm for this...
>>
>> http://en.wikipedia.org/wiki/Five_color_theorem#Linear_time_five-coloring_algorithm
>>
>> I'd be interested to hear if anyone on the list has already got an
>> implementation of this. Perhaps some clever bit of GeoServer ?
>
> Nope, we don't have anything like that. As far as I can see this would
> have to be done in pre-processing anyways, first a full scan of the
> data and then assign the colors?
>
> A tool could be used to load the data, build a connectivity map,
> assign the colors, and generate a SLD using FID filters to assign
> the 5 colors to the different polygons.
>

I have a paper on how to create the adjacency graph
(http://www.citeulike.org/group/9502/article/6600150) that is on my to
do list (but quite low down it :-) I can mail a copy of the PDF to
anyone who's interested.

Ian
-- 
Ian Turton