Could this be done using a rule-based expression through the creation of a variable that returns the pixel-size area of a polygon / pixel-size length of a line?
On Thu, Sep 12, 2013 at 3:28 PM, Matthias Kuhn <matthias.k...@gmx.ch> wrote: > 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 > >>> Qgis-developer@lists.osgeo.org > >>> http://lists.osgeo.org/mailman/listinfo/qgis-developer > >> > >> > >> > >> > >> _______________________________________________ > >> Qgis-developer mailing list > >> Qgis-developer@lists.osgeo.org > >> http://lists.osgeo.org/mailman/listinfo/qgis-developer > >> > > > > _______________________________________________ > > Qgis-developer mailing list > > Qgis-developer@lists.osgeo.org > > http://lists.osgeo.org/mailman/listinfo/qgis-developer > > > _______________________________________________ > Qgis-developer mailing list > Qgis-developer@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/qgis-developer >
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