[GRASS-user] v.patch drops adjacent polygons

[A. Marcia BARBOSA]

> Probably a problem with topology. What is the output of  v.build
> map=utm10_31to34?

$ v.build map=utm10_31to34
Building topology ...
260900 primitives registered
Building areas: [...]
85544 areas built
0 isles built
Attaching islands:
Attaching centroids:
Topology was built.
Number of nodes     :   173844
Number of primitives:   260900
Number of points    :   0
Number of lines     :   0
Number of boundaries:   174340
Number of centroids :   86560
Number of areas     :   85544
Number of isles     :   0
Number of incorrect boundaries   :   4433
Number of centroids outside area :   1016

--No changes that I can spot..

> As with the two islands, probably some incorrect boundaries were the two
> tiled original vectors touch. Try v.clean tool=bpol,rmdupl type=boundary
> (break polygons, then remove duplicates) on the patched map. Maybe some
> snapping is needed. Visual inspection of the area were the two vectors
> touch should give you some idea about what's wrong.

$ v.clean input=utm10_31to34 output=utm10_31to34_clean type=boundary
tool=bpol,rmdupl
[...]
Rebuilding topology for output vector map...
Building topology ...
260423 primitives registered
Building areas:  100%
86503 areas built
1 isles built
Attaching islands:  100%
Attaching centroids:  100%
Topology was built.
Number of nodes     :   173845
Number of primitives:   260423
Number of points    :   0
Number of lines     :   0
Number of boundaries:   173863
Number of centroids :   86560
Number of areas     :   86503
Number of isles     :   1
Number of incorrect boundaries   :   215
Number of centroids outside area :   57

--And now the map has many of the contact-zone polygons that did not
appear before v.clean... but not all.
The two original vectors look fine and are perfectly adjacent when
displayed, with all polygons built.
I'm attaching zoom-in image of part of the contact zone (vertical line
in the middle), with the first patched map (dark grey) and the cleaned
patched map (light blue). The white spaces should have also been
filled with polygons (some of them quite narrow).

Cheers
Márcia
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