When I polygonize a raster, I very often have 'pixels' holes/interior ring that touches exterior ring.
An example:
POLYGON((5 0, 10 0, 10 10, 0 10, 0 0, 5 0, 3 3, 5 6, 7 3, 5 0))
It's defined as an invalid geometry in the OGC geometry specifications.
In QGIS, how to fix this?