[GRASS-dev] Re: [GRASS GIS] #254: wxpython Layer Manager: higher raster hides the lower (GRASS GIS)

[Michael Barton]

On Aug 14, 2008, at 8:41 AM, <grass-dev-request at lists.osgeo.org> <grass-dev-request at lists.osgeo.org 
 > wrote:

> ----------------------- 
> +----------------------------------------------------
>  Reporter:  giohappy  |       Owner:  grass-dev at lists.osgeo.org
>      Type:  defect    |      Status:  closed
>  Priority:  critical  |   Milestone:  6.4.0
> Component:  wxGUI     |     Version:  svn-develbranch6
> Resolution:  fixed     |    Keywords:
>  Platform:  Linux     |         Cpu:  x86-32
> ----------------------- 
> +----------------------------------------------------
> Comment (by martinl):
>
> Replying to [comment:2 giohappy]:
>> I think the mistake is the fact that in the wxGUI the raster is
> displayed without -o flag as default, as it is in the tcltk GUI.
>
> You can change default settings in GUI Preferences dialog, tab  
> "Command",
> "Raster settings". I am not quite sure if '--o' should be defaut for
> d.rast as it is in TCL/TK GUI.

I think that the default behavior of d.rast and the subsequent  
addition of the -o flag is an historical artifact of the days before  
GRASS rasters had null support. At that time, "0" values could mean a  
values of 0 OR null values. Or nulls could be indicated by other  
values like -999.

Now that there is null support for rasters, the default behavior of  
rasters should be that nulls are transparent during overlays, although  
the option to make them opaque should be retained.

The -o flag is additionally problematic in that it is very similar to  
the --o flag which means "overwrite" in other contexts. We will need  
to keep the -o flag for the GRASS 6 series, but I would recommend  
changing it to something else for GRASS 7. Do we need to keep opaque  
nulls the default for GRASS 6?

In the GUI, I recommend making the -o flag the default behavior in the  
preferences and allowing users to turn it off if they desire. I  
suspect that most people expect (and want) nulls to be transparent by  
default--unless they are experienced GRASS users who already know  
about this historical artifact.

Michael

Michael