[GRASS-user] Question about layers and categories

Vincent Bain bain at toraval.fr
Thu Apr 4 09:24:27 PDT 2013


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. Should I purge categories
from the layer I want to delete (with v.category command) prior to
remove layer ?

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).

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

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)


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