[Qgis-developer] Status of Release 1.7 and Raster-on-the-Fly

[mayeul.kauffmann at free.fr]

Here are some comments about the second part (which is more a user issue).
>"draw speeds of about 30 seconds"  "I was impressed that QGIS could handle such a large dataset. Any comments?"


You might gain speed gains doing some or part of the following:
- put your dataset in a database (suggested: postgis or spatialite)
- simplify your dataset for visualisation at small (overview) scale; try to draw non-simplified data only at detailed (large) scale
- if you insist on shapefiles, make sure you created the spatial index (there is one button in QGIS for this)
- probably it does not make sense to display all the data at all scale. Depending on semantic needs, optimisation is possible here. In addition, polygons with a very small area can easily be ignored at small scale (they would probably be displayed with a single pixel anyway): pre-compute the scale of each polygon, and create a scale based rule in rule based renderer. (or use a query at the layer level).
When you say "contour polygon" do you mean level curves (elevation data) [hence: might be linestring, not polygons]? Then at small scale you could show only main level curves (every 100 m).
Doing this I can browse the Openstreetmap dataset + level curves/contour for a European country (>1Gb of data) with a rendering time of less than 1 second.
If you have several layers, you may want to try and build the threading branch for even faster rendering (multicore).
Mayeul



----- Mail Original -----
De: "Bob Bruce (CON)" <Bob.Bruce at gov.mb.ca>
À: "qgis-developer at lists.osgeo.org" <qgis-developer at lists.osgeo.org>
Envoyé: Jeudi 17 Mars 2011 16h53:25 GMT +01:00 Amsterdam / Berlin / Berne / Rome / Stockholm / Vienne
Objet: [Qgis-developer] Status of Release 1.7 and Raster-on-the-Fly

I am preparing to do a presentation on QGIS to a GIS users group meeting in Brandon on Friday. What can I say about when 1.7 will come out? Will it have the Raster-on-the-Fly capability that is being tested at the moment?

I have been doing some testing with a polygon file of contours have 54614 polygons and it is 770 Mb in size and an getting draw speeds of about 30 seconds on my DELL T3500 system running Windows 7 with 4 Gb of RAM. The contour polygons are at 5m intervals. (I have some screen captures of some of the draws if people want to email me directly for them) This seems like a pretty fast response time and I was impressed that QGIS could handle such a large dataset. Any comments?

        Bob Bruce


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