[GRASS-dev] [GRASS GIS] #251: Enhancements to vector querying

[GRASS GIS]

#251: Enhancements to vector querying
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 Reporter:  cmbarton      |       Owner:  grass-dev at lists.osgeo.org
     Type:  enhancement   |      Status:  new                      
 Priority:  major         |   Milestone:  6.4.0                    
Component:  Vector        |     Version:                           
 Keywords:  query vector  |    Platform:  All                      
      Cpu:  All           |  
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 About 9 months ago, I suggested an overhaul of the GRASS vector query
 framework (original post <http://lists.osgeo.org/pipermail/grass-dev/2007-
 September/033173.html>)

 Now that work has started on GRASS 7 in ernest, I'd like to reiterate
 this. Besides giving GRASS a simpler and richer query ability, it would
 permit much easier GUI interface to vector querying--such as interactively
 drawing a box or polygon around points to select them for query in the new
 database table manager.

 So here is the idea. It involves some upgrades to modules we already have,
 but no new modules. The nice thing is we are almost there. I'll also drop
 this in the bug tracker as an enhancement suggestion.

 '''v.select (query using a vector map):'''
 1. add flags -p and -g for text output instead of creating a new map. It
 would report which map(s) and feature(s)/cat(s) meet the query criteria.
 2. allow multiple maps to be selected. This would directly address Eric's
 question. If the output is a map, it would be the equivalent of v.patch on
 all queried vector elements.
 3. add operators "contains" and "adjacent". Contains=all vector features
 whose nodes are completely inside a polygon (or inside or touching the
 boundary). Adjacent=all vector features who share a node/point or
 line/boundary with the selecting feature. Because GRASS is topologically
 correct, adjacency information is readily available.
 4. maybe change option names from ainput and binput to selector and
 selected or queried. This would have to wait until GRASS 7, of course. I
 find ainput and binput not very clear where used in other vector
 operations either (maybe I'm just dense).

 '''v.what (query using coordinates): '''
 1. add flags -p and -g for current behavior (-pg could be the default if
 we wanted to do this before GRASS 7)
 2. add "output=" option to allow v.what to create a new map from the
 results of its query, like v.select does
 3. allow multiple maps for input, as with the suggestion for v.select
 4. allow coordinates to be read optionally as a line or area/boundary (-l
 or -a?) instead of only as individual points.
 5. add operators overlap, contains, adjacent. (This also would make
 possible interactive vector selection with a mouse drawn box or polygon
 from the GUI) In other words, have v.select and v.what work the same
 except that v.select uses a vector map for querying and v.what uses a set
 of coordinate points.

 '''v.overlay (boolean combination of maps):'''
 1. drop the ainput and binput. Replace with just input.
 2. allow multiple maps to be entered into input, not just 2
 3. deprecate v.patch because v.overlay with the OR operator replaces it.
 (If we wanted to do this before GRASS 7, we'd have to create a new module,
 maybe named v.combine or something like that because this changes the
 default behavior of v.overlay)

 Michael

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Ticket URL: <http://trac.osgeo.org/grass/ticket/251>
GRASS GIS <http://grass.osgeo.org>