[GRASS5] [bug #4075] (grass) grass and postgis issue

Kirk R. Wythers kwythers at umn.edu
Fri Feb 10 09:38:31 EST 2006

Hi Moritz,

On Feb 9, 2006, at 2:50 PM, Moritz Lennert wrote:

> So, if you import into GRASS vector format, the geometry is stored  
> in the
> GRASS format, even if the data is in a postgres table (geometry and  
> data
> are handled separately in GRASS. This means that it is no longer a  
> postgis
> vector layer, but a GRASS vector layer. Postgis columns in the  
> table or
> spatial indices will have no impact as the geometry is not in  
> postgres.

This may be a silly question... but what then, is the point of  
building GRASS with postgis support? If postgis is really only an  
extension that adds geometry column and spatial indexing options to  
postgresql, and GRASS does not use the posgis geometry, then why  
bother with postgis?

Perhaps the answer to my question is that I do see a speed up with  
spatial queries run from GRASS through db.execute (or when I run them  
on the database with postgreql). You were right btw Moritz, the slow  
response to the command d.vect seems to be at due to the time it  
takes d.vect to 'draw'. The same query run in postgis is quite fast.  
Also, if I make the query more selective so that fewer data points  
get returned. d.vect returns faster (I think because there is less to  
draw). Does that make sense to you?

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