v.category problem - was Re: [GRASS-dev] Keywords, help pages...

[Trevor Wiens]

On Tue, 29 Aug 2006 20:19:20 +0200
"Radim Blazek" <radim.blazek at gmail.com> wrote:

-snip-
> > Radim,
> >
> > By this logic, then to add centroids one should specify boundary not
> > area, because no areas exist before you add a centroid. In which case
> > this still doesn't make any sense.
> 
> Areas exists, but they dont have any category. In GRASS (not QGIS)
> you can query vector map with areas without category, you get area size
> but no category. You cannot specify boundary because each area can be
> defined by many boundaries and thos boundaries can be linked to a different
> table, e.g. a boundary can be a road (typical in TIGER for example).

I stand corrected. I double checked and yes, although they aren't
recognized for vector to raster conversion, they are reported as
existing.

> 
-snip-
> but objects  compund of boundaries. If a user asks to add a category
> to area, the only way to do it is to place a centroid (if does not exists).
> That is not completely inconsistent.

No, but certainly not obvious. One of my main beefs against ESRI is the
lack of clarity, adherence to standard terminology, etc. For the most
part I've found GRASS raster module to be quite clear and consistent on
this front, but the way functionality has been packaged into the v.*
modules to be a different story. This has been the reason for my past
complaints (naming of attribute table links layers) and now the hiding
of adding centroids in a v.category module is very frustrating. If
GRASS wants to attract new users we need to do a better job than ESRI.

Actually although much of the vector processing in GRASS 6.x is very
powerful, I don't use it all that often because it is just too awkward
in comparison with the simple elegance of PostGIS, especially in terms
of attribute management. 

-snip-
> 
> If 'most people' I am not sure. In any case you cannot change module options
> in 6.x line, that would definitely break user scripts and third party apps.

OK I'll rephrase that. Users familiar with other GIS programs, will not
at first find adding centroids, in v.category.

All that said, if v.category sacrosanct (although it is unclear to me
how this is determined) the issue remains of how to make things better.
Eric Patton has off list offered to improve some of the documentation
for v.category based on this discussion. I think however, it would be a
good idea to add in Hamish's v.centroids script with help page into the
CVS as it provides an obvious and convenient way of doing this for
users not deeply familiar with the GRASS 6.x vector modules. I also
liked the idea of a v.dissolve script which would make things more
convenient and obvious.

T
-- 
Trevor Wiens 
twiens at interbaun.com

The significant problems that we face cannot be solved at the same 
level of thinking we were at when we created them. 
(Albert Einstein)