Nikos A wrote: > >> > 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). Nikos A: > > 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). Markus Metz: > No, it does change the geometry directly. O-K. This is where I am confused. > > 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. I'll try to consult the programmer's manual or else about the vector data model. I need to clarify this to myself :-). > Therefore adding a new layer will modify the geometries directly. IOW, > categories and layers are part of the (GRASS) vector geometry objects. Rigth, I need to (re-)define to myself the "geometries" term. > Also, layers and categories have nothing to do with topology. A-ha... > 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. Will check the manuals... > 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. Danke Markus. I am not really confused over the layer/db-connection stuff. Rather, it is the topology - geometry - categories and layers stuff that I am confused about. Nikos _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
