[GRASS-dev] Spatial vector selection by another vector without creating a new vector

GRASS GIS GRASS GIS developer
1

Hi,

given following workflow:

- Polygon vector A, line vector B
- Spatially select those polygone in A which are e.g. touched by some lines
in B
- open attribute table, view entries selected by step before
- update some columns of the selected entries

as this workflow is available in mostly all modern desktop GIS, I couldn't
find a smart way in GRASS GIS to do this.

any hints are welcome.

If it is not implemented, should I open an enhancement ticket because it is
a common needed workflow?

-----
best regards
Helmut
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2

On 17/05/16 23:21, Helmut Kudrnovsky wrote:

Hi,

given following workflow:

- Polygon vector A, line vector B
- Spatially select those polygone in A which are e.g. touched by some lines
in B
- open attribute table, view entries selected by step before
- update some columns of the selected entries

as this workflow is available in mostly all modern desktop GIS, I couldn't
find a smart way in GRASS GIS to do this.

any hints are welcome.

Brainstorming:

- Create a column line_cat in vector A
- Use v.distance with dmax=0 to get upload cat value of line that crosses polygon
- v.db.update on the other column using where="line_cat is not null"

This could be wrapped up in a script...

If it is not implemented, should I open an enhancement ticket because it is
a common needed workflow?

This has been briefly mentioned as one advantage of 'virtual maps', discussed as an alternative to cat/where parameters in vector modules [1].

I agree that "on-the-fly" selection of features by others would be quite useful. I use this quite a lot in QGIS for example (e.g. through the spatial queries plugin). Although, I haven't seen an option to update a column just for selected features. I use it, for example, to calculate statistics on vector attributes only for those that are selected, etc.

Moritz

[1] https://trac.osgeo.org/grass/ticket/1798#comment:12