[GRASS-dev] v.out.ogr exports more features than available

Maris Nartiss maris.gis at gmail.com
Wed Dec 14 02:16:54 EST 2011

OK. When creating a new test dataset I understood where's the problem:
v.clean rmdupl will remove duplicate geometries and will merge
categories resulting in single geometry, multiple categories
(acceptable in GRASS)
v.out.ogr can not export multiple categories to Shapefile as it
doesn't support such construct. v.out.ogr "fixes" it by duplicating
geometry and assigning one of categries (+ rest of attributes) to
cloned geometry thus one geometry = two cats turn to two geometries =
single cat for each.
It makes sense from data preservation point, still it might be
confusing to see that v.out.ogr can export more features than are
present in vector dataset (needs a warning here!) and it might totally
ruin cleaned data as I was using GRASS only to remove duplicate
features from the data set.

Sometimes GRASS vector model is too powerful...

Sorry for noise,

2011/12/14 Maris Nartiss <maris.gis at gmail.com>:
> Hello,
> yes, I used QGIS to verify count of exported features in Shapefile and
> indeed count matched with one reported by v.out.ogr as "written
> feature count".
> And now comes the best - g.copy and v.extract both had NO effect on
> result -> resulting dataset still was exported with ALL points present
> before v.clean. I run both ways twice to avoid PEBKAC.
> And now the worst thing - GRASS 6.4.2 is also affected. I'm opening
> ticket and blocking release till we will figure out what's exactly
> wrong. If somebody has an idea, I can send dataset off-list for
> testing.
> Maris.
> 2011/12/14 Hamish <hamish_b at yahoo.com>:
>> Benjamin wrote:
>>> Sounds like v.out.ogr includes some
>>> features in
>>> the output that are marked "dead" but are still in the
>>> dataset. Could you check two things, please:
>> ...
>>> 2) and make a copy of the cleaned vector points map
>>> using g.copy vect=, and use v.out.ogr to export
>>> the copy instead of the cleaned original?
>> "v.extract cat=1-99999999" might help too.
>> Hamish
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