[GRASS-dev] v.select features without category skipped

[Moritz Lennert]

On 17/11/16 14:11, Luca Delucchi wrote:
> Hi devs,
>
> this morning I got a problem with v.select, I don't understand if is a
> bug or what... I repeated the procedure with north carolina dataset
>
> g.region vect=zipcodes -ap
>
> v.mkgrid map=zipcodes_grid box=10000,10000
>
> v.category zipcodes_grid opt=report
> Layer/table: 1/zipcodes_grid
> type       count        min        max
> point          0          0          0
> line           0          0          0
> boundary       0          0          0
> centroid      42          1         42
> area           0          0          0
> face           0          0          0
> kernel         0          0          0
> all           42          1         42
>
> v.select ain=zipcodes_grid bin=zipcodes operator=touches
> out=zipcodes_grid_final --o
> WARNING: Vector map <zipcodes_grid_final> already exists and will be
>          overwritten
> Processing features...
>  100%
> Processing areas...
>  100%
> Writing selected features...
>  100%
> Writing attributes...
> WARNING: Array of values to select from column <cat> is empty

i.e. no features found which is logical, as there are no zipcode areas 
that touch a grid area. 'touches' is normally defined as [1]

"a touches b: they have at least one boundary point in common, but no 
interior points."

Try with intersects, overlaps, etc.

I agree though that the error message is very unclear. After the "Array 
of values ... is empty" it should just stop. After a very rapid look at 
main.c of v.select it seems to me that it doesn't check the result of 
the selection and just goes on trying to write a new file...

Moritz

[1] https://en.wikipedia.org/wiki/DE-9IM