[QGIS-Developer] GEOS 3.9 and fixed precision model

[Andreas Neumann]

Hi, 

GEOS 3.9 will have some significant improvements for us. 

I'm citing from an e-mail thread from strk: 

"GEOS-3.9 will have the new overlay engine enabled by default, so
nothing to do there. Martin (Davis) believes there will be no more
TopologyExceptions with the new code but I think in order to be 100%
sure a fixed precision model should be used, which is possible to do
with the newly exposed functions taking a grid size. In case QGIS uses
some kind of precision model, it would be good to use those." 

----------- 

Recent QGIS versions also have a "precision / grid" setting per layer in
the layer properties dialog (Geometry and Topology restrictions). There
you could set the geometry precision, let's say to mm. 

I'd like to discuss with you devs how the QGIS and GEOS precision
settings can be "integrated" in the future - and used more extensively
throughout QGIS. E.g. a processing algorithm or model could
automatically read these values and pass them on to GEOS for running the
geometry operations. Also, when using the interactive editing tools
(e.g. splitting and merging, basically anything that involves GEOS),
this precision setting should be honored. 

I'd like to get an idea if this is useful/feasible and how much effort
would be necessary (approximately) - will this require funding? 

-------------- 

Also - it would be good to discuss when the switch to GEOS 3.9
will/should be made, esp. for OSGEO4W. 

Thanks for joining this discussion, 

Andreas
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