[GRASS-user] v.overlay snapping

Stephane Goldstein s.n.g at gmx.com
Wed Jul 17 21:03:10 PDT 2019

I am getting a weird result when using v.overlay since I upgraded from
version 7.4 to 7.6.

I am using GRASS 7.4 trough the QGIS Processing Toolbox, in Arch Linux and
Grass 7.6 trough the QGIS Processing Toolbox in a Windows VM (since getting
this unexpected results I downgraded my Grass installation back to 7.4 in

One common step in my workflow is to vectorize a raster (using v.to.rast)
and then overlay the result with an hexagonal grid.

Since version 7.6, it seems that the result does snapping vertices of the
two overlapping features when they are too close to each other. Even if I
specify snapping = -1.

I'm not sure if I am missing something or if I should file a bug report. I
put together some files that can be used to reproduce the error:

- hexagons_ext.gpkg: an extract of the hexagonal grid
- raster_ext.gpkg: an extract of the raster
- overlay_ext_7.4.gpkg: overlay of both with the "and" operator, using
Grass 7.4, with the desired result
- overlay_ext_7.6.gpkg: overlay result using Grass 7.6 containing undesired
- errors.gpkg: points where snapping is occurring

Any help is appreciated.

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