[GRASS-user] Select specific layer when copying vector map

[Moritz Lennert]

On 09/08/16 13:48, Johannes Radinger wrote:
> Hi,
>
> I'd like to create from an existing GRASS vector map that has 3 layers
> (with three attribute tables) a new vector map that has only one
> layer and its associated attribute table (here the information related
> to layer 3).
>
> What I am doing so far (in python):
>
> # First copy the map to a new one and copy table (that of layer 3)
> # that I want to re-connect to new map
> grass.run_command("g.copy",
> overwrite=True,
> vector="oldmap,newmap")
> grass.run_command("db.copy",
> overwrite=True,
> from_table="table_layer3",
> to_table="table_layer3_copy")
>
> # Second delete all tables of the newmap
> for i in [1,2,3]:
> grass.run_command("v.db.droptable",
> flags="f",
> map="newmap",
> layer=i)
>
> # Third reconnect a table to the newmap
> grass.run_command("v.db.connect",
> overwrite=True,
> map="newmap",
> table="table_layer3_copy")
>
> When I check in the attribute table manager, there is only one layer
> listed (layer 1).
> Similarly, v.db.connect reports:
> v.db.connect -p map=newmap
> Vector map <newmap> is connected by layer <1/table_layer3_copy> table
> <table_layer3_copy> in database [...]
>
> However, in d.vect I can still select from all three layers that were in
> the old map (-1,1,2,3),
> and all of them can be displayed (with -1 specified)?
> So does may newmap have three layers or only one?

3. Layers are defined by category values, not by attribute tables.

>
> How can I make the third layer the default layer 1 and remove all other
> layers?
> Or is there a way to copy a vector map with just a single layer and its
> associated table specified as default?

Try v.extract instead of g.copy.

Moritz