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I have a "geometry" and a "rating" column. I want to symbolize the geometries in an SLD (PolygonSymbolizer) but fill it with a color value that is interpolated between BLUE-PURPLE-RED based on the rating value, in range -100 to +100.

So the polygon would have a single fill color, but the color should be dynamic, based on the value.

I tried superimposing two symbolizers with scaled alpha values for the fill color: -100 to 0.0, +100 to 1.0 for red and the negated value for blue, but that doesn't work correctly because I get different results depending on whether I do red first and then blue or the other way around.

http://i.imgur.com/P8cmV5X.png

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    I could just add 21 rules for every decile (and 0) but that seems like an awful lot of work!
    – Wouter Lievens
    Commented Nov 16, 2014 at 10:43
  • Since my layer is based on a view, I "solved" it by adding this column: color2hex(cast(round((rating / 200.0 + 0.5) * 255) * 65536 + round((rating / -200.0 + 0.5) * 255) as integer)) as color With a custom SQL function. Hardly a "clean" solution though.
    – Wouter Lievens
    Commented Nov 16, 2014 at 10:50

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When searching for a solution for "colour gradient based SLD for polygons" I found this page: http://docs.geoserver.org/stable/en/user/styling/sld/tipstricks/transformation-func.html

Excerpt: "Interpolate transforms a continuous-valued attribute into another continuous range of values."

GeoServer provides a solution, but it is not called something with "gradient".

I hope this helps.

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  • Thank you! The "interpolate" function is exactly what I was looking for.
    – Gael Lafond
    Commented Jun 9, 2020 at 3:18

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