Hi Matthias, Thanks a lot for your answer. Unfortunately, I have no sponsors for this. I asked to improve my knowledge on this topic ;) Perhaps we could raise a crowdfunding for this improvement ?
Cheers, Michaël 2016-07-05 15:31 GMT+02:00 Matthias Kuhn <[email protected]>: > Hi Michaël, > > There are a couple of possibilities to improve the performance of > operations in two ways (which both help here AFAICS) > > * Give QgsExpression::prepare() more power > * Compile functions (where possible) > > The send one depends to some degree on the first one. > > Let me know if you have sponsors, I've got some experimental code > somewhere and I am very interested in working on this project. > > FYI, a first test - only the prepare part - some months ago improved the > 2.5D rendering by ~30%. > > Regards > Matthias > > On 07/05/2016 03:11 PM, kimaidou wrote: > > Hi all, > > > > I am a bit curious about performances concerning the use of Spatial > > expressions in QGIS, for example to select features like this > > > > intersects( > > $geometry, > > geom_from_wkt( 'MultiPolygon (((649308.28000000002793968 > > 6978002.05999999959021807, 649295.32999999995809048 > > 6977994.54999999981373549, 649235.92000000004190952 > > 6978013.50999999977648258, 649182.53000000002793968 > > 6978077.32000000029802322, 649212.34999999997671694 > > 6978159.53000000026077032, 649308.28000000002793968 > > 6978002.05999999959021807)))') > > ) > > > > NB: I have simplified the WKT representation here > > > > I am running this expression inside QGIS 2.14, for a layer containing > > approx. 100 000 features ( buildings). > > The WKT polygon represents a very small area compared to the whole > > layer: 500 features only are selected. > > > > It seems to me no spatial index is used, because it takes some time to > > run ~ 3 minutes. > > > > I have checked the option to run expressions server side, and all the > > layers are PostGIS layers. > > > > What could be done to improve this kind of expressions, which can be > > used elsewhere in QGIS ( to toggle labels for example ) ? > > > > Regards > > Michaël > > > > > > _______________________________________________ > > Qgis-developer mailing list > > [email protected] > > List info: http://lists.osgeo.org/mailman/listinfo/qgis-developer > > Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-developer > > > _______________________________________________ > Qgis-developer mailing list > [email protected] > List info: http://lists.osgeo.org/mailman/listinfo/qgis-developer > Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-developer
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