[Qgis-developer] Custom raster drawing

Marco Hugentobler marco.hugentobler at karto.baug.ethz.ch
Tue Jun 12 10:19:10 EDT 2007

Hi Barry and Tim,

I agree with Tim that the raster code in QGIS needs a complete redesign. The 
IRC meeting on Friday would be fine for me.

 > I want to display some rasters with a very specific colour scheme:

 > values from 0 to 0.9: gray (or maybe green. Something neutral)
 > from 0.90 to 0.95 : gray to yellow
 > from 0.95 to 0.99 : yellow to orange
 > from 0.99 to 1.00 : orange to red
> ...
> I think this is outside my timeframe though - I'd like to get this done in 
>a matter of weeks.

But can't you just use the raster transparency branch to do this? The solution 
there is not nice from a design point of view, as it adds just a new drawing 
mode. But it should do for the short time.
Load a raster, open the properties dialog, set 'Color Map' combo box 
to 'Custom Colormap' and go to tab 'Colormap'. Then set number of entries to 
5, set 'Color interpolation' to 'Linearly' and press 'Classify'. Then double 
click on the values to enter 0, 0.9, 0.95, 0.99, 1. Then double click on the 
color boxes to set 0 to gray, 0.9 to gray, 0.95 to yellow, etc. and 
press 'Apply'.


Dr. Marco Hugentobler
Institute of Cartography
ETH Zurich
Technical Advisor QGIS Project Steering Committee
marco.hugentobler at karto.baug.ethz.ch

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