[gdal-dev] Performance issues with gdal vrt

[Craig Leat]

Hi

I am having performance issues with gdal raster vrt files and since I
am not experienced with this format I am hoping someone can offer some
advice. I built the vrt files from a collection of MrSid images using
gdalbuildvrt. I then used sed to add the <NODATA> tag and changed from
<SimpleSource> to <ComplexSource>. I am using QGIS to view the data
and working with the MrSid files directly is fast, however working
with the same collection via the vrt file is VERY slow. The MrSid
files contain overviews and I wish to know if there is anything I need
to do to make these overviews available to the vrt driver? I have
noticed that my CPU usage is around 90% while QGIS tries to load the
vrt and this seems strange to me for a task that I expect to be disk
intensive.

My system is Ubuntu 9.04, gdal 1.6.1 and QGIS trunk r11732.

Many thanks,

Craig