[Qgis-developer] Re: classification of rasters

[Marco Hugentobler]

Hi Peter,

Am Montag, 19. März 2007 13:33 schrieb Peter Ersts:
> > I'm not sure I undestand what you mean. Do you mean that, if there is
> > stretching enabled and custom colormap, there should be a combination of
> > both?
> > Maybe I can understand better with an example. Let's say we have a DTM
> > and there is clipping and stretching enabled for values 500 - 800. But in
> > custom colormap tab there are items 400 red / 600 green / 1000 blue and
> > linear color interpolation. How would the application behave in such a
> > situation?
>
> So yes, I am suggesting there should be a combination of both. In your
> example: the DTM values 500 - 800 get stretched from 0 to 255 for
> rendering. In this case the color map could also be scaled so that  0 =
> red 85= green and 255 = blue, but this is only done at during rendering,
> the table values still stay the same (i.e. 400 - 1000). It may not
> always make sense to do both but I am looking at if from a clarity and
> usability standpoint for the user. If it is only going to be one or the
> other, the we need to add quite a but more to the GUI to make it clear
> that the user that they only have one option or the other.

Hm, for me it seems as if stretching and custom colormap contradict each other 
in this example. From stretching, it follows that 500 is 0 and thus red =255, 
green=0, blue=0. But from the custom colormap it follows that 400 is plain 
red and 500 has already more green and less red.

Is this correct or did I overlook any important point / use case?

>If it is only going to be one or the
> other, the we need to add quite a but more to the GUI to make it clear
> that the user that they only have one option or the other.

Yes, true. One possibility would e.g. be to have an additional entry 'custom 
colormap' in the combo box. So if there is the 'pseudo colors' item active, 
then user has stretch/clip and 'colormap' tab is disabled. If there 
is 'custom colormap' active, then 'band selection' group is disabled 
and 'colormap' enabled.

I'm sure there are more user friendly possibilities. What do you think?

cheers,
Marco