Bug report #21354

SAGA Difference wrong result

Added by Lene Fischer about 5 years ago. Updated about 5 years ago.

Affected QGIS version:3.5(master) Regression?:No
Operating System: Easy fix?:No
Pull Request or Patch supplied:No Resolution:up/downstream
Crashes QGIS or corrupts data:No Copied to github as #:29172


Using SAGA Difference in processing I try to create a new layer with the result as a difference between the two layers.
It gives a 'strange' result.
I have controlled for illegale geom, overlap and duplicates - OK

If I use select by location the result is correct.

Data added in Geopackage

test.gpkg (500 KB) Lene Fischer, 2019-02-22 07:30 PM

test_saga_232.jpg (552 KB) Pedro Venâncio, 2019-03-04 12:59 PM

test_saga_720.jpg (509 KB) Pedro Venâncio, 2019-03-04 12:59 PM


#1 Updated by Nyall Dawson about 5 years ago

  • Resolution set to up/downstream
  • Status changed from Open to Closed

This bug is in saga itself - use the native QGIS difference tool instead, it's well tested, faster, and more robust.

#2 Updated by Pedro Venâncio about 5 years ago

This seems a bug in SAGA version 2.3.2, used by QGIS.

I've just tested Difference algorithm with Lene dataset in native SAGA 2.3.2 and 7.2.0, and 2.3.2 gives the problem described, but 7.2.0 gives the correct result, as you can see in the images attached.

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