[GRASS-user] RE: Problem querying layers other than '1' in gis.m

Dylan Beaudette dylan.beaudette at gmail.com
Wed Sep 20 13:39:49 EDT 2006

On Wednesday 20 September 2006 08:09, twiens wrote:
> ----- Original Message Follows -----
> From: Michael Barton <michael.barton at asu.edu>
> To: Moritz Lennert <mlennert at club.worldonline.be>, "Patton,
> Eric" <epatton at nrcan.gc.ca>
> Cc: "'grassuser at grass.itc.it'" <grassuser at grass.itc.it>
> Subject: Re: [GRASS-user] RE: Problem querying layers other
> than '1' in gis.m
> Date: Wed, 20 Sep 2006 07:48:43 -0700
> > You CAN link multiple tables to single vector objects.
> > That is what layers is all about. You need a separate CAT
> > column for each table you link. Each cat column is a
> > "layer". It serves as a key to link the object with a
> > record in a table.
> >
> > I don't know if v.what (used in gui vector querying) will
> > query more than layer one. There was some discussion about
> > this awhile back and I can't remember the outcome. There
> > have been some other new changes to v.what that will
> > eventually go into 6.3. If layer support has been added,
> > this will go into 6.3 also.
> v.what does not support layers.
> Eric,
> Your understanding of what layers are supposed to do is
> correct, they are multiple linked tables to a single
> topology layer, but there are unique cats for each linked
> table.
> Michael and Eric,
> I had been planning on adding support for multiple linked
> tables in v.what at some point, but since I deeply dislike
> the terminology and think the general approach to this
> problem is wrong in the first place I'm not motivated.
> Personally I think that attribute management should be left
> to the database backend and this so called feature should be
> dropped as the terminology is confusing. But.... there is
> deep resistance from a number of core developers who
> designed and implemented this multiple table link feature,
> so that is not likely to happen. The short and long of it
> however, is that there are other aspects of GRASS
> development which I'm more interested in and I think are
> more useful so that is where I have been and will be putting
> my limited time. If someone else wants to add "layers" to
> v.what that is fine, but I won't be doing it in the
> forseable future.
> T
> --
> Trevor Wiens
> --
> Trevor Wiens
> twiens at interbaun.com


thanks for the insight into some of the behind the scenes GRASS development. 
perhaps this would be a good topic for the steering committee to discuss? 
querying attributes (often from multiple linked tables) is an important tool, 
but if there is an underlying disagreement (with alternative data storage / 
terminology approaches) I am fairly sure that others would be interested in 
hearing about it, and possibly giving feedback (what do you think David 
S. ?).


Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis

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