[QGIS-Developer] Heads up on GEOS Overlay New Generation

[Andreas Neumann]

Hi Régis, 

Indeed interesting. 

Is there evidence that it will also be faster than previous versions? If
yes - for certain operations or generally faster? 

We had issues in the past with the "Geometry checks" that you could
define on a layer (Layer Properties --> Digitizing settings) - tests
about overlays and gaps. It was always slow and not so reliable. Once
you tried to fix one error you would get even more errors through the
fix and then you would end up with even more errors when trying to fix
the error ... Hopefully, this will work better then ... 

Greetings, 

Andreas 

On 2020-09-17 09:33, Régis Haubourg wrote:

> Hi there, 
> I'm forwarding a call [0] from Paul Ramsey and the JTS-GEOS teams. 
> I've been following this closely for 3 years now and we have been providing testing and test datasets to try to help here. 
> 
> In short, GEOS provides most of the geometry computations tools to PostGIS QGIS & al. The intersection, difference etc.. (overlay operations) suffered from using full numeric precision and lacked snapping and rounding operations. 
> 
> Thus our libraries were slow, and prone to topology errors due to those numeric precision issues. Most of us have seen intersections or union operations failing from time to time. 
> 
> The new overlay operation implements snap rounding operations (which is implemented in ESRI tools for instance) and will provide fast and robust operations. 
> 
> Now it is available in the 3.9 branch of GEOS. 
> 
> As QGIS uses GEOS extensively in editing, displaying and algorithms, we have to take a look seriously at the positive impacts and potential regressions. 
> 
> Paul warns that they spotted no regression in Z handling, which probably means the test coverage is very low in GEOS CI, and we might expect regressions on the Z handling here, especially for snapping I bet. 
> 
> Anyhow this is GREAT news for the OSGEO community because this was one major glass ceiling for us. We sometimes had no choice than switching to GRASS topological operation to do some very basic operations. Hopefully these times are gone :) 
> 
> And combined with subdividing features, we should gain a massive order of magnitude in speed for overlay. 
> 
> Time to test this big win! 
> 
> Best regards 
> 
> Régis 
> 
> [0] https://lists.osgeo.org/pipermail/geos-devel/2020-September/009670.html 
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