On Thu, Jun 6, 2013 at 12:28 PM, Nikos Alexandris <n...@nikosalexandris.net> wrote: > Nikos Alexandris: > >> > Still, I find it counter-intuitive that it's required to create a new >> > vector map to achieve that. >> > >> > --%<--- >> > v.category in=wrs2_tiles_of_interest_testing@PERMANENT layer=2 option=add >> > >> > ERROR: Output vector wasn't entered >> > --->%-- > > Markus Metz wrote: > >> Because you need to modify vector geometries in order to add a new >> layer. Categories and layers are first and foremost stored together >> with the geometries. Whenever geometries are modified, the result will >> be a new vector map (with the exception of v.edit and the digitizers). > > Just for (even more) completeness and understanding: adding a new layer does > not really change the geometries per-se (that is the topology, the shape).
No, it does change the geometry directly. > It's the inner design of the vector data model, i.e. the fact that categories > and layers are bound together. > > Is it wrong to describe it as an internal "indexing" issue or similar? Yes, it is wrong. Categories and layers are first and foremost stored together with the geometries. Therefore adding a new layer will modify the geometries directly. IOW, categories and layers are part of the (GRASS) vector geometry objects. Also, layers and categories have nothing to do with topology. A new layer really is only added by modifying the geometries, only after that you might want to attach a table to that new layer. I guess you confuse layer with database connection. The existence of a layer is a condition for an optional database connection. A database connection itself does not mean the layer of this connection actually exists. Markus M _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user