[Qgis-developer] Problems in clipping lines with polygons

[Giovanni Manghi]

> http://www.faunalia.eu/~paolo/test_clip.tar.xz
> There are two polygons and one line, with the result of the clip with
> qgis and gdal algs.

it seems you hit a corner case.
The qgis tool returns the right result, while the ogr based clip gives
that topology error (ERROR 1: TopologyException: Input geom 1 is
invalid: Self-intersection at or near point 1629973.9531249425
4886529.3203125177 at 1629973.9531249425 4886529.3203125177)

the curios thing is that
a) not even st_isvalid returns anything wrong (so cleaning with
st_makevalid does not make any difference)
b) the qgis geometry checker does not find any auto-intesection, but
finds slivers. Trying to fix them results in an error and the output
gets only one of the two polygons.

bottom line, the qgis and ogr based tools do work fine, when
geometries are ok, and here we return to the other day email about how
we can improve the checking/fixing geometries in processing. The
problem here described seems really something very odd, that I cannot
investigate more now.

-- G --