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

[Régis Haubourg]

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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