[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

From: qgis-developer-request at lists.osgeo.org
Date: Sunday, March 22, 2009 6:00 am
Subject: Qgis-developer Digest, Vol 37, Issue 36
To: qgis-developer at lists.osgeo.org

> Send Qgis-developer mailing list submissions to
> 	qgis-developer at lists.osgeo.org
> 
> To subscribe or unsubscribe via the World Wide Web, visit
> 	http://lists.osgeo.org/mailman/listinfo/qgis-developer
> or, via email, send a message with subject or body 'help' to
> 	qgis-developer-request at lists.osgeo.org
> 
> You can reach the person managing the list at
> 	qgis-developer-owner at lists.osgeo.org
> 
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of Qgis-developer digest..."
> 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/qgis-developer/attachments/20090323/970197df/attachment-0001.html


More information about the Qgis-developer mailing list