[GRASS-dev] Vlib: how to delete an object from a GRASS vector map

[Martin Landa]

2008/8/23 Martin Landa <landa.martin at gmail.com>:
>> On Thu, Aug 21, 2008 at 6:54 PM, Benjamin Ducke
>> <benjamin.ducke at oxfordarch.co.uk> wrote:
>>> I am struggling to understand how to delete an object, including its
>>> attached attributes, from a GRASS vector map.
>>>
>>> I open the map with:
>>>
>>> Vect_open_update ( &Map, MAPS[i].tempname, mapset );
>>>
>>> Then I find the category IDs of the objects I want to delete and then I
>>> do:
>>>
>>> Vect_delete_line ( &Map, cat );
>>> Vect_field_cat_del ( Cats, field, cat );
>
> the second argument of Vect_delete_line() is feature id not category.
> Feature ids start at 1. You get number of features by
> Vect_get_num_lines().

I forgot to mention, to get list of feature ids which have given
field/category use

Vect_cidx_find_all(..., cat, list);

then

for (i = 0; i < list->n_values; i++) {
    Vect_delete_line(&Map, list->value[i];
}

Note that you need to open vector map at topology level (2) to use
Vect_cidx_find_all(..., cat, list) otherwise you need to read all
features and check their category manually.

-- 
Martin Landa <landa.martin gmail.com> * http://gama.fsv.cvut.cz/~landa *