[GRASS-dev] [GRASS GIS] #1798: all relevant vector modules should have cats and where parameters

[GRASS GIS]

#1798: all relevant vector modules should have cats and where parameters
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 Reporter:  mlennert              |       Owner:  grass-dev@…              
     Type:  enhancement           |      Status:  new                      
 Priority:  normal                |   Milestone:  7.0.0                    
Component:  Vector                |     Version:  svn-trunk                
 Keywords:  where cats parameter  |    Platform:  Unspecified              
      Cpu:  Unspecified           |  
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Comment(by mlennert):

 Replying to [comment:6 mmetz]:
 > Replying to [comment:5 hellik]:
 > > Replying to [comment:4 mmetz]:
 > > >
 > > > IIUC, these virtual maps should behave just like normal maps: from a
 user perspective, it could look like
 > > >
 > {{{
 > v.extract -v (-v as new flag to create a view or virtual vector)
 > v.buffer
 > }}}
 > > >
 > > > instead of
 > > >
 > {{{
 > v.extract
 > v.buffer
 > }}}
 >
 > [Sorry, I meant v.extract]
 > >
 > > AFAIU a virtual map could be a "permanent" selection by cats/where,
 store this virtual map in the mapset and use this virtual map as input for
 processing by the v.*-modules.
 > >
 > >
 > {{{
 > v.make.virtual input=vector output=virtualmap cat=1-10 where A < 10
 > v.* input=virtualmap
 > }}}
 >
 > The advantage of a virtual map over using v.extract to get a "permanent"
 selection by cats/where is not clear to me because the result of v.extract
 can be processed faster than a virtual map.

 The only real advantage I can see is if whenever you modify the original
 map, your virtual map gets modified also (just like a database view). You
 then don't have to run v.extract each time. Also, you might consider it
 useful to avoid clutter if you can list views separately from vector maps
 (i.e. g.list view).

 But, again, I personally think that cats/where parameters do solve much of
 the issue and a virtual map then would only save you the typing of these
 parameters.

 Moritz

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Ticket URL: <http://trac.osgeo.org/grass/ticket/1798#comment:7>
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