[GRASS-user] v.overlay snapping

[Markus Metz]

On Thu, Jul 18, 2019 at 6:07 AM Stephane Goldstein <s.n.g at gmx.com> wrote:
>
> I am getting a weird result when using v.overlay since I upgraded from
version 7.4 to 7.6.

this was a bug in finding line intersections, fixed in d729e94:
https://github.com/OSGeo/grass/commit/d729e9406ac1bff0d68b0e10b3de44b62bc2d064

Markus M

>
> 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 Linux)
>
> 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 snapping
> - errors.gpkg: points where snapping is occurring
>
> Any help is appreciated.
> Thanks,
> Stephane
>
> Download link:
> https://send.firefox.com/download/0a9efe8d5669941b/#mmdtLo-ZYMgSoORqeNMwkQ
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