Details Ticket 1566


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Serial Number 1566
Subject vector data select by attribute
Area wish
Queue grass
Requestors b.wood@niwa.co.nz
Owner none
Status open
Last User Contact Mon Feb 5 21:56:24 2007 (2 yr ago)
Current Priority 30
Final Priority 70
Due No date assigned
Last Action Mon Feb 5 21:56:24 2007 (2 yr ago)
Created Mon Feb 3 05:37:03 2003 (6 yr ago)

Transaction History Ticket 1566


Mon, Feb 3 2003 05:37:03    Request created by guest  
Subject: vector data select by attribute

grass binary for platform: Compiled from Sources
GRASS Version: 5.0.0 (Aug 2002)

Improved support for selecting vector data by attribute (eg: 200m contours from
a vector map of contour data) and to select from multiple maps to create a new
map (or ideally to create a virtual map with pointers to the data, which may
optionally be saved as a new map).

I'm not sure if the 5.1 data management in PostGreSQL/PostGIS will permit this
through the use of db views, if GRASS 5.1 can access such views as maps. If so,
then the wish is coming true :-)


Thanks,

   Brent Wood
Mon, Feb 3 2003 10:48:37    Mail sent by blazek@itc.it  
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From Radim Blazek <blazek@itc.it>
To Request Tracker <grass-bugs@intevation.de>, grass5@grass.itc.it
Subject Re: [GRASS5] [bug #1566] (grass) vector data select by attribute
Date Mon, 3 Feb 2003 10:48:27 +0100
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On Monday 03 February 2003 05:37 am, Request Tracker wrote:
> this bug's URL: http://intevation.de/rt/webrt?serial_num=1566
> -------------------------------------------------------------------------
>
> Subject: vector data select by attribute
>
> grass binary for platform: Compiled from Sources
> GRASS Version: 5.0.0 (Aug 2002)
>
> Improved support for selecting vector data by attribute (eg: 200m contours
> from a vector map of contour data) and to select from multiple maps to
> create a new map (or ideally to create a virtual map with pointers to the
> data, which may optionally be saved as a new map).
>
> I'm not sure if the 5.1 data management in PostGreSQL/PostGIS will permit
> this through the use of db views, if GRASS 5.1 can access such views as
> maps. If so, then the wish is coming true :-)
>
>
> Thanks,
>
>    Brent Wood

Standard way to do this in 5.1 (format and db driver independent) is:
v.extract where=
v.patch

It is true that you can use views, but it is not intended for
normal usage.

Radim


Thu, Feb 13 2003 05:54:41    Mail sent by guest  
The Genamap GIS has a very nice facility for creating virtual maps. A select
from one or more vector maps can be stored as a virtual map. It appears to
create an index (or set of pointers) to the underlying features in each map.
This means that the map features are not physically extracted & used to buils
a new map, which is very fast & requires minimal space. Such virtual maps
(called active ID's) can be save as a new map if required.


I find this functionality very convenient. I believe from what I have read
about GRASS 5.1 that a view created as a sequence of selects joined by union
statements in a PostgreSQL/PostGIS database comprising a GRASS 5.1 mapset
would supply comparable functionality. 

Is there any reason in the GRASS 5.1 architecture why this view approach to
map management is inappropriate.

Thanks,

  Brent
Thu, Feb 13 2003 09:56:21    Mail sent by guest  
PostGIS is only one of 3 (later 4) supported formats and grass should work
for all formats in the same way, if possible. Support for such feature 
for one format only does not seem to be best to me.

The problem for PostGIS format is that each line is identified by unique
ID, UNION ALL will return duplicate IDs unless imput tables were generated
with different ranges of IDs.

Radim
Mon, Feb 5 2007 21:56:24    Mail sent by mneteler  
Brent,

is the problem solved with a current GRASS 6 version?

Markus
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