[GRASS-user] v.patch -a: how to interpret message "Line -58728 already has area/isle -1611 to left"

[Markus Metz]

On Mon, Aug 20, 2018 at 5:42 PM, Moritz Lennert <
mlennert at club.worldonline.be> wrote:
>
> I am trying to patch together a series of vector maps, using v.patch -a
(apparently without -a, category values are not retained).  These maps
contain polygons that were extracted from the same base map (but in each
map there are different polygons than in the others), treated with
different intermediary steps, to then be all put back together in a new
vector map.
>
> However, for one of these maps, when I try to add it, I get:
>
> WARNING: Line -58728 already has area/isle -1611 to left
> ERROR: Unable to add isle (map closed, topo saved)
>
> How should I interpret this message ?

This is a problem with registering a new area. The warning is coming from
https://trac.osgeo.org/grass/browser/grass/trunk/lib/vector/diglib/plus_area.c#L718
and the error is coming from
https://trac.osgeo.org/grass/browser/grass/trunk/lib/vector/Vlib/build.c#L140

Try to patch without building topology, i.e. v.patch -b, then clean with
v.clean -c tool=bpol,break type=boundary

HTH,

Markus M


>
> Moritz
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