[Qgis-developer] slow raster loading

[Tim Sutton]

Hi

On Wed, Aug 10, 2011 at 8:31 AM, Marco Hugentobler
<marco.hugentobler at sourcepole.ch> wrote:
> Btw, is it possible to call computeMinMax() on demand, e.g. in
> QgsGDALProvider::minimumValue /maximumValue instead of the provider
> constructor?
>
> It probably does not matter much for the desktop experience. However, for
> server throughput, avoidance of opening and parsing the aux.xml file could make
> a difference.
>

I think the overhead for reading the aux.xml file is really minimal
and the min/max population of that if its not there is quite quick and
a once off event so I wouldnt think it is going to impact the server
much. I'd suggest I first run some benchmarks to see how much overhead
it adds.

Regards

Tim

> Regards,
> Marco
>
>
> Am Dienstag, 9. August 2011, 21.46:45 schrieb Tim Sutton:
>> Hi Paolo
>>
>> Does it do that every time you load that layer or only the first time?
>> Does the filesystem permissions allow writing of gdal .aux.xml files?
>>
>> My raster stats branch merge changed some behaviours and it is
>> probably a side effect of that. One of the changes is that gdal gets
>> full stats when trying to determine the min max of a band. It will
>> fetch those stats quickly from aux.xml if present of if not its going
>> to do a full stats gather just for the basic min max stats which is
>> where you probably experience the slowness. I will see if I can find a
>> better way to do the basic min/max stats gathering.
>>
>> Regards
>>
>> Tim
>>
>> On Tue, Aug 9, 2011 at 3:49 PM, Paolo Cavallini <cavallini at faunalia.it>
> wrote:
>> > Hi all.
>> > With current master, I get bad performances in loading rasters (a <12Mb
>> > takes >5 sec); when double-clicking it from the QGIS browser, it is far
>> > slower (>20 sec). From the console:
>> > Warning: Object::connect: No such signal QgsGdalProvider::statusChanged(
>> > QString ) in
>> > /storage/build/Quantum-GIS/src/core/raster/qgsrasterlayer.cpp:2446 Any
>> > hint?
>> > All the best.
>> > --
>> > Paolo Cavallini: http://www.faunalia.it/pc
>> > _______________________________________________
>> > Qgis-developer mailing list
>> > Qgis-developer at lists.osgeo.org
>> > http://lists.osgeo.org/mailman/listinfo/qgis-developer
>
>
> --
> Dr. Marco Hugentobler
> Sourcepole -  Linux & Open Source Solutions
> Churerstrasse 22, CH-8808 Pfäffikon SZ, Switzerland
> marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
> Technical Advisor QGIS Project Steering Committee
>



-- 
Tim Sutton - QGIS Project Steering Committee Member (Release  Manager)
==============================================
Please do not email me off-list with technical
support questions. Using the lists will gain
more exposure for your issues and the knowledge
surrounding your issue will be shared with all.

Visit http://linfiniti.com to find out about:
 * QGIS programming and support services
 * Mapserver and PostGIS based hosting plans
 * FOSS Consulting Services
Skype: timlinux
Irc: timlinux on #qgis at freenode.net
==============================================