[Qgis-developer] Data for QGIS Hackfest
Bob Bruce
Bob.Bruce at shaw.ca
Mon Mar 23 08:27:09 EDT 2009
Hi Andreas:
thanks for getting back to me. I appreciate your suggestions for improving the performace of my data with QGIS. I had not tried any of these improvements, except for building an index for my vector data, which didn't make any improvements in performance. I could do a little bit of generalization of the vector data but I am not displaying it at a small enough scale to vastly improve the performance for the amount of time required to do this.
If you have a FTP site where I could put this data then please let me know and I will make it available to you.
Bob
----- Original Message -----
From Andreas Neumann <a.neumann at carto.net>Date Sun, 22 Mar 2009 13:00:03 +0100To qgis-developer at lists.osgeo.orgSubject Re: [Qgis-developer] Data for QGIS HackfestHi Bob,
The QGIS is now over, as far as I know, but your data might still be
useful for performance testing of QGIS trunk.
I'd like the mention that the display of very large rasters is normally
not a problem if you used gdaladdo to add pyramids to your data. You can
use rasters with the hundreds of gigs of filesize without a bottleneck.
You'd have to build the pyramids however. If you store your data in
multiple files instead of just one, you should build a tileindex with
gdaltindex. See http://www.gdal.org/gdal_utilities.html for more infos.
You should definitively give the display of rasters in qgis a try - they
should perform well.
The display of big vector data is another issues. Did you build spatial
indices? Are you directly loading from the shapefiles or from postgis?
In realworld scenarios you should use various scale levels and reduce
your vector data with SQL WHERE clauses (e.g. only display major rivers
in a river network). If you display tenthousands/hundredthousands of
vector features in one display, you probably have generalization and map
reading problem anyway. There is no value in displaying all of your
vector features, say on a state level when you totally clutter your map
display and can't distinguish individual features anymore.
This doesn't mean that performance shouldn't be improved in QGIS. I just
mean that there are ways for you to improve performance with the
existing QGIS by improving the data structure of your existing data.
Andreas
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