[GRASS-user] v.extract and layer/table settings with layer=2

[Moritz Lennert]

Am 27. November 2018 20:51:37 MEZ schrieb Johannes Radinger <johannesradinger at gmail.com>:
>Hi all,
>
>this is maybe I quite easy routine for somebody that is using v.extract
>regularly.
>
>Here my challenge: I have a vector map (initially created by v.net
>tools)
>that has several layers and associated tables to each layer. Now for
>further processing I want to extract only some features from layer=2
>and
>the corresponding attribute table.
>
>I can do that using "v.extract input=mymap1 layer=2 where='mycol=x'
>output=mymap2". The resulting 'mymap2' has an attribute table connected
>to
>layer 2 and there are no other layers (e.g. there is no layer 1, which
>is
>considered in most grass tools as default layer). So I wanted to change
>that and to shift layer 2 (and the attribute table) to layer 1 using
>"v.category option=chlayer layer='2,1' input=mymap2 output=mymap3"
>
>...however, this does not change the attribute table connection (as
>checked
>by "v.db.connect -p "). So I guess I also have to use v.db.connect in
>some
>way (??) to get the attribute table shifted from connection at former
>layer
>2 to layer 1 (unused).

Yes:

v.db.connect -d layer=2
v.db.connect layer=1 table=


>
>In my opinion this is quite a bit complicated, considering that I just
>wanted to extract some features from a 3-layered map?? Is there a
>easier
>way or a general description if one want to extract some feature that
>are
>not stored in layer 1?

The best would probably be some form of output_layer parameter in v.extract, probably with a default of 1. Worth a trac ticket I think.

Moritz