Bug report #21457

The "avoid intersection" operation fails with NO warnings if existing polygon has an auto intersection

Added by Giovanni Manghi about 5 years ago.

Affected QGIS version:3.4.5 Regression?:No
Operating System: Easy fix?:No
Pull Request or Patch supplied:No Resolution:
Crashes QGIS or corrupts data:Yes Copied to github as #:29274


When the "avoid intersection" is enabled but the existing feature has an auto-intersection, then the new polygon will NOT be clipped along the borders of the existing one.
Moreover QGIS does not show any warning, not in the message bar or even in the LOG.

This can easily led to very wrong results, unless using a semi-transparent symbolgy that allows to inspect/see how the new polygon boundaries really are.

Seen in 3.* and as well in the last release of 2.18.

tagging as "high" as it can lead to wrong results with no warning at all.

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