[GRASS-user] Not matching categories/line IDs

Markus Metz markus.metz.giswork at gmail.com
Thu Sep 13 13:26:03 PDT 2018

On Thu, Sep 13, 2018 at 10:50 AM Johannes Radinger <
johannesradinger at gmail.com> wrote:
> Hi all,
> I am a little bit puzzled about the actual number of lines/categories of
a specific vector map (river network). As discussed yesterday, the output
of v.category with the report option provides a column 'count' which is a
feature count. Running v.category option=report on my vector provides me
> v.category input=Ebro_river_vector_poly_clean_tmp at Ebro2_alien_spread
> Layer/table: 1/Ebro_river_vector_poly_clean_tmp
> type       count        min        max
> point          0          0          0
> line         804          1       1053
> ....
> This would indicate that I have 804 line features. However, using the
tool v.info on the same vector I get following different result regarding
the number of lines:
> v.info map=Ebro_river_vector_poly_clean_tmp at Ebro2_alien_spread

>  | Name:            Ebro_river_vector_poly_clean_tmp
>  ...
>  |   Number of points:       0               Number of centroids:  0
>  |   Number of lines:        799             Number of boundaries: 0
> ...
> And even more puzzling, I then added a table to this vector map and the
output of v.db.addtable is:
> v.db.addtable map=Ebro_river_vector_poly_clean_tmp at Ebro2_alien_spread

> Reading features...
> Updating database...
> 803 categories read from vector map (layer 1)
> 803 categories read from vector map don't exist in selection from table
> 803 records updated/inserted (layer 1)

If there are 804 features, 2 features must have the same category value,
resulting in 803 updates to the database
> So, is it 804,799 or 803??

The output of v.info and v.category option=report must be identical with
regard to the count of features.
> The map I am using is a polyline river network (cat=first) that has gone
trough the tool v.clean with the options:
break,rmdupl,rmline,rmsa,rmdangle. The number of lines and cats before the
cleaning tool is 805 (consistent output among all tools).
> So I am wondering what happens during cleaning and how to get a clean map
with a corresponding table that has entries for each cat, and were each cat
represents one line feature (i.e. that the number of cats/line features is
consistent over the multiple tools).
> Please let me know if I should share the vector map (and how, which

Ideal would be a stripped down GRASS mapset with only this vector
Ebro_river_vector_poly_clean_tmp. Exporting the vector would change the
geometry representation and it would no longer be possible to reproduce the

Markus M
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