Just do it the hard/smart way.

Google for some test suits with invalid geometries, run them in QGIS with the 
different methods and write a summary.

Or so it the fun(ny) way and create your own invalid geodata. 
Self-intersecting, overlapping etc.

— 
Von einem iPhone gesendet und wird daher Fehler enthalten.

> Am 22.05.2019 um 12:08 schrieb DelazJ <[email protected]>:
> 
> Hi Jürgen,
> 
> I know that we don't have black box and this was certainly not the 
> appropriate term to use. Sorry. Still, most of the users have no means to 
> read the code but need to use any of these options. Without understanding 
> what they do, it becomes simply a click-click business (not empowering them). 
> So it could be nice we shed some light on them (maybe something for a grant 
> proposal?).
> 
> Greetings,
> Harrissou
> 
>> Le mer. 22 mai 2019 à 11:55, Jürgen E. Fischer <[email protected]> a écrit :
>> Hi Harrissou,
>> 
>> On Wed, 22. May 2019 at 11:03:56 +0200, DelazJ wrote:
>> > *> The QGIS method is an internal method that can return multiple errors
>> > and was > IIRC introduced, when GEOS could just report one error at a time
>> > without a > location and we couldn't or didn't yet use it threaded.
>> > Essentially it was > just made to highlight digitizing errors.  It might
>> > miss some rules or > interpret some edge cases differently than GEOS.*
>> > 
>> > So there are some historical reasons. Unfortunately, this does not seem
>> > enough to clarify things and wouldn't deserve a place in the docs (I may be
>> > wrong!).  If anyone has more details, please tell us. I think it could be
>> > worth clarify and document the differences if they are clear enough or
>> > merge the tools in the future if possible, avoiding confusion for users (we
>> > should not have kind of black box ;) in QGIS).
>> 
>> We don't have a blackbox.  The ultimate source of information about the QGIS
>> method is the QGIS method:
>> 
>> https://github.com/qgis/QGIS/blob/master/src/core/qgsgeometryvalidator.cpp
>> 
>> But there isn't a comparison on what GEOS and that method do differently.
>> 
>> 
>> Jürgen
>> 
>> -- 
>> Jürgen E. Fischer           norBIT GmbH             Tel. +49-4931-918175-31
>> Dipl.-Inf. (FH)             Rheinstraße 13          Fax. +49-4931-918175-50
>> Software Engineer           D-26506 Norden            https://www.norbit.de
>> QGIS release manager (PSC)  Germany                    IRC: jef on FreeNode
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