[QGIS-Developer] GEOS 3.9 and fixed precision model

[Andreas Neumann]

Here some additional info:
http://lin-ear-th-inking.blogspot.com/2020/06/jts-overlayng-noding-strategies.html


Maybe it would be good to open a QEP for this? Since I am not so
familiar with QGIS inner architecture, it would be best if someone who
knows it better, would start such a QEP. 

I will suggest the Swiss QGIS user group to invest next year in data
quality improvements - so any outcome/follow-up work of such a
discussion could potentially be funded. 

Andreas 

On 2020-11-27 09:16, Andreas Neumann wrote:

> 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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