[Qgis-developer] color ramps for vector graduated symbols (ticket #782)

[Barry Rowlingson]

Marco Hugentobler wrote:

>>The MatLab colour map editor is show here (scroll down a little for a
>>screenie):
>>
>>http://tinyurl.com/27gbra
> 
> 
> That looks great!

  I wrote a colour ramp editor in Python for Qt, based on some C++ 
source I think I found in the Qt examples. It returns a 
QtGui.QLinearGradient object. You get the little triangles for dragging 
around the map, you can double click to add new colours and so on.

  Go here and get rampEditor.zip, then run "python RampEditor.py" - its 
only two files and extracts to the current directory:

http://www.maths.lancs.ac.uk/~rowlings/Geog/Qgis/

  (obviously you need PyQt4 module for your python).

  I wrote it as a widget that can be inserted into dialogs. When you run 
the example you'll see my gradient widget and a "colour square" widget 
below. This is for testing drag-n-drop. Right-click on the colour square 
(I should add a double-click option) to choose a colour, then drag and 
drop this onto the gradient bar.

  Gradient bar triangles can be dragged and double-clicked. I'm sure 
they can be deleted... Somehow... Oh, maybe that needs adding. I think 
there may be some off-by-one errors in the triangle placement too.. This 
is work in progress....

  The grooviest ramp editor I've seen is in Adobe Illustrator, where you 
basically draw a spline that interpolates between your colours in 
whatever colour space you are interested in. Hence you can easily create 
colour ramps in hue and saturation as well as linear RGB values.

  Also, it may also be worth looking into the ColorBrewer palettes for 
presets for classifications:

http://www.personal.psu.edu/cab38/ColorBrewer/ColorBrewer_intro.html

Barry