On Thu, Apr 4, 2013 at 6:24 PM, Vincent Bain <[email protected]> wrote: > Hi, > > I hope the questions to come are not too stupid, but I need some help > about some points that remain to me unclear about vector layers & > category management : > > Let's take the case of a point vector produced by v.to.point module. You > know this command creates a 2 layers vector, consisting in: > - 2 distinct tables, > - 2 sets of categories. > > The first point is when removing a layer, categories associated with > this layer /remain/ attached to the geometry.
How did you remove a layer? If you used v.db.connect -d or v.db.droptable, then you deleted the link of an attribute table to a layer. As you observed, categories for this layer will remain attached to the geometry as reported by v.category op=report. > Should I purge categories > from the layer I want to delete (with v.category command) prior to > remove layer ? Do you want to remove the attribute table or the categories attached to the geometry objects? Usually it does not harm to have categories attached to geometries in multiple layers. > > When I remove layer 1, trying to query layer 2 points in wxGUI display > window, the result appears in the terminal but the classical pop-up does > not rise (whatever "layer" parameter in d.vect). The wxGUI query ignores d.vect options and will (should) report anything found in any layer. > > Then I try to change layer "2" to number "1" (v.category with > option=chlayer layer=2,1). The command performs without apparent > problem, but v.to.db -p tells me the expected layer 1 is still number > 2... Can you post the output of v.to.db -p? I did a quick test and v.to.db does not tell me anything about an expected layer number... > > In a word, all this is very confusing. > Could anyone help me to point at what is going wrong, either in my > understanding of attribute handling or in possible issues in the > commands I use (v.to.db, v.category) In short, categories and associated layer numbers are stored with the geometry. Category numbers for a given layer are used as key for the link to an attribute table for the given layer. IOW, you need a vector geometry object with a category number for a given layer and that category number existing in the key column of the corresponding attribute table in order to have attributes linked to the given object and layer. HTH, Markus M > > Thanks, > Vincent > > > > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
