[GRASS-user] v.overlay snapping

GRASS GRASS user
,
1

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 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

2

On Thu, Jul 18, 2019 at 6:07 AM Stephane Goldstein <s.n.g@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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