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

Trevor Wiens twiens at interbaun.com
Wed Sep 27 01:46:12 EDT 2006

On Tue, 26 Sep 2006 17:06:13 +0200
Radim Blazek wrote:

> In theory you could move the relations to a database as suggested Trevor,
> but it would be difficult and not efficient to reflect any operations
> on geometry in database. 
> It is very easy to assign 2 cats to the overlapping parts
> from 2 input areas, to do that in database (from GRASS) is much more complex.
> If you want, you have to move to database everything, i.e. also geometry.

I completely disagree. It would be very easy to describe overlapping
areas with database attributes, in fact, IMO much easier than with
layers. You are correct however, that storing this information
internally in GRASS is more efficient for the very small percent of the
time where a module will need to reference this information for some
purpose other than getting a list of objects to consider for
processing. Right now almost all modules allow for some filtering by a
query so AFAICT using arbitrary queries to replace the 'layers feature'
would have a negligible impact on performance in most cases. If this is
not the case please elaborate.

It does not follow that moving attribute management into the database
requires the movement of geometry as well, or at least you've not
demonstrated it, only stated it.

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)

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