Hi Matthias, Thank you for your preliminary results. I think they are encouraging to further look into this issue.
Andreas Am 12.09.2013 10:28, schrieb Matthias Kuhn: > Hi, > > How would you define small? I guess something can already be done with > scale based visibility, but that needs preprocessing of the data and > assigning some kind of "size class". > > On Don 12 Sep 2013 08:51:43 CEST, Andreas Neumann wrote: >> Hi, >> >> Another interesting thing would be to simplify features when you zoom >> out. Maybe simplifying would be quicker than rendering thousands of >> unnecessary vertices. Optionally this could also be "outsourced" to the >> database - many databases support simplification on the db level. I >> don't know if it would really speed up things. One would have to test. > > I did a preliminary analysis for this. > I created a view on a postgis DB containing ~17000 line features with > the geometry column simplified to 10m in the view. > > *Non Simplified* > ./output/bin/qgis_bench --iterations 20 --width 1024 --height 768 > bench-full.qgs > iterations: 20 > total_avg: 0.4246 > total_max: 0.657 > total_maxdev: 0.2324 > total_min: 0.407 > total_stdev: 0.0535176606364665 > > *Simplified* > ./output/bin/qgis_bench --iterations 20 --width 1024 --height 768 > bench-simplified.qgs > iterations: 20 > total_avg: 0.09615 > total_max: 0.098 > total_maxdev: 0.00184999999999998 > total_min: 0.095 > total_stdev: 0.000792148975887722 > > 0.42 / 0.09 is more than 400% performance improvement for this simple > case. > > The results of course depend heavily on the particular setting, but I > think this looks indeed like a road we should have a look into. > > (Setup: PostGIS 2.0.3 in a kvm virtual machine on the same physical > machine. No styling at all took place on the layer) > > Matthias > >> >> Andreas >> >> >> >> Am 12.09.2013 07:57, schrieb aperi2007: >>> Not always is preferrable to suppress the small features. >>> Often in our rendering we prefere to substitute a small rendering of >>> kind polygon with a point rendering at lowest scales. >>> >>> This is possible using the Rule-Rendering >>> also is possible to use the rule-rendering to define a rule that in a >>> scale interval and with a dimension interval the feature is render using >>> a point rendering and change in a polygon rendering when the scale grow. >>> >>> Andrea. >>> >>> On 12/09/2013 02:13, Nyall Dawson wrote: >>>> Hi all, >>>> >>>> I've been chatting with Nathan about adding a feature to QGIS which >>>> would allow suppression of rendering features smaller than a set >>>> threshold for vector layers. (There's already a similar function in >>>> the labelling engine "Suppress labeling of features smaller than"). >>>> This feature would come in handy for me for several tables which >>>> contain a wide range of very small -> very large features, which cause >>>> slow rendering at small scales. >>>> >>>> I'm just checking that if I code this up it's not going to be >>>> duplicated effort - Nathan is under the impression that someone else >>>> has been talking about adding something similar. Is there currently >>>> any plans for a feature like this, or should I get started? >>>> >>>> Nyall >>>> >>>> >>>> >>>> >>>> >>>> _______________________________________________ >>>> Qgis-developer mailing list >>>> [email protected] >>>> http://lists.osgeo.org/mailman/listinfo/qgis-developer >>> >>> >>> >>> >>> _______________________________________________ >>> Qgis-developer mailing list >>> [email protected] >>> http://lists.osgeo.org/mailman/listinfo/qgis-developer >>> >> >> _______________________________________________ >> Qgis-developer mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/qgis-developer > > _______________________________________________ Qgis-developer mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-developer
