Tobias,
Indeed Buffer 0 won't do any good on self intersections. Thats just not
the way to repair them.
Hence I wrote "Buffer 0 on INVALID geometries IMHO can lead to good
results depending on the /nature of the invalidity/. To my experience
/repeating points,//wrong coordinate ordering and holes touching outer
shells in one point///are being repaired well without data loss.".
Of course self intersections can be easily overlooked. For that we have
validity checkers.
Marco
On 29-10-19 19:35, Tobias Wendorff wrote:
Hi Marco,
Am 29.10.2019 um 10:49 schrieb Marco:
Buffer 0 on INVALID geometries IMHO can lead to good results depending
on the nature of the invalidity. To my experience repeating points,
wrong coordinate ordering and holes touching outer shells in one point
are being repaired well without data loss.
I'm sorry to say that the side effects are worse. Maybe the
implementation of QGIS is wrong, but try the example below.
Please enlighten me with a few links to the tons of tests on the web
showing that buffer 0 is destroying data. My Google skills are not up to it.
I've just updated the example I'm normally showing students with an
actual thematic, I'm calling in "wronxit": [1]
Try to "buffer(geom, 0)" it in QGIS...
This problem isn't constructed (well, this geojson is of course), but
I'm got lots of self-intersecting polygons from different sources all
the time. "Buffer 0" is destructive here and since many
self-intersections are damn small, most users simply don't see them.
"Fix Geometries" gives the correct result.
Best regards,
Tobias
references:
[1] https://gist.github.com/tobwen/39bc3562d1cb957cbaf4305ef53f77df
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