Re: [Geotools-gt2-users] Geotools Rule Description

[Andrea A. <aa...@op...>]

Michael Bedward ha scritto:
> Ah someone who understands SLD... it's dangerous admitting that Ajay -
> people will ask you questions :-)
> 
> I've seen examples of filling polygons in a small number of different
> colours depending on the value of a data attribute.  But do you know
> if there is a way of specifying a colour ramp or category relationship
> between the fill and an attribute's value in the SLD file ?

There is no built-in way to do so, at least not for vector data,
only the raster symbolizer has a ColorMap concept (which is in
fact a way to declare a color ramp).

Yet, not all hope is lost. The fill color can take pretty much
any expression inside of it, so it can also take a filter
function. Filter functions are pluggable, so you can write
a custom one, register it in the GeoTools SPI (the plugin
mechanism GeoTools and JAI use), and use it in your SLD.
The result would look like:

<CSSParameter name="fill">
   <ogc:Function name="colorRamp">
      <ogc:PropertyName>myAttribute</ogc:PropertyName>
   </ogc:Function>
</CSSParameter>

or maybe you can add all params to make a color ramp
explicit, such as the array of colors and values.
Maybe something like:

<CSSParameter name="fill">
   <ogc:Function name="colorRamp">
      <ogc:Literal>#FF0000,#00FF00,...</ogc:Literal>
      <ogc:Literal>0,120,...</ogc:Literal>
      <ogc:PropertyName>myAttribute</ogc:PropertyName>
   </ogc:Function>
</CSSParameter>

That is, the first two arguments being two strings
that you'll then parse into a list of colours and
a list of values.

Cheers
Andrea

-- 
Andrea Aime
OpenGeo - http://opengeo.org
Expert service straight from the developers.