[Qgis-developer] Data for QGIS Hackfest

[Andreas Neumann]

Hi 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

Bob Bruce wrote:
> I am pleased to see that you're having the hackfest to improve QGIS. 
> If want some data to test with QGIS, I have lots. I have a 2500 km 
> sq area of northern Manitoba having topographical mapping with 7 
> layers and 30 shape files of 234 Mb. This mapping was done with 
> orthophotography of .5m pixels and is quite detailed. You are welcome 
> to use that dataset for testing QGIS,
>
> I have found significant performance issues in QGIS with this data the 
> draws take at least 30 seconds for an area of 50 km X 34 km for the 
> water layer. I could FTP it to you. I haven't even tried loading the 
> ortho photos which are .5m resolution and are 5 km X 5 km with a file 
> size of 293Mb.
>
> I can FTP this dataset to a site of your choosing if you want to use it.
>
>    Bob Bruce
>
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