Proof of Concept Gradient Coloring and Dev question

[Frank Warmerdam]

On Apr 5, 2005 3:42 AM, Havard Tveite <havard.tveite at umb.no> wrote:
> I agree that it would be nice to have a way of rendering
> quantitative attributes in UMN Mapserver semi-automatically.
> 
> What about making the functionality more "general" by for
> instance including the following STYLE items:
> 
> NUMBEROFCLASSES - the number of classes used (if not speficied,
>                    a "continuous" rendering is performed).
> BREAKS - The method of classification - "naturalbreaks",
>           "equalinterval", "histogramequal", ... or the actual
>           breakpoints ("1000,5000,7000,13000,21000,26000,29000").
 
Håvard,

While the idea of generalizing this to generating a set of 
classes has merit, I don't think it is suitable when you 
use Bill's method of putting the controls in a STYLE.  In
fact, Bill's approach is to say that there would only be one
class for gradient fill (what I would call color ramped) and that
it is implemented as a specialized rendering style but STYLES
are nested inside a single class.  So we can't very well have a
class with a style that generates a set of classes.   At the very
least it would be very confusing. 

Of course we could just call these "subclasses" breaks, but 
then you still end up duplicating alot of the descrete class
mechanism.  Better to just manually or though mapscript
create a set of descrete classes if that is what you want. 

I certainly do like Bill's original approach for continuous gradient
fill.  In addition to using it for the rendering, I would also like legends
to know how to show a gradient fill styled class as a color ramp with
min, max and perhaps some intermediate values.  Of course we will
also need some control over how these legend entries are generated.

PS. I would be interested in implementing the same STYLE mechanism
for rasters if you changes make it into CVS.  But we would still need 
someone to tackle the legend support. 

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent