[Qgis-developer] slow raster loading

[Tim Sutton]

Hi

On Thu, Aug 11, 2011 at 1:48 PM, Giovanni Manghi
<giovanni.manghi at gmail.com> wrote:
> Hi Tim,
>
> I'm wrong or after the last commits QGIS is not gathering raster stats
> anymore?
>

They should be.

> At least in my box the aux.xml files are not created anywhere.

Try going to the histogram tab of your raster properties or do
something else that requires stats. In many cases, stats are not
needed so you may not be seeing thm gathered. Also for read only
medai, the stats should land up in the proxy dir which is set to
~/.qgis/gdal_pam. Otherwise can you give me a specific procedure to
follow to replicate?

Regards

Tim

>
>
> Cheers
>
> -- Giovanni --
>
>
> On Wed, 2011-08-10 at 11:50 +0200, Tim Sutton wrote:
>> 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)
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