[gdal-dev] [Qgis-developer] Large raster (ecw) identify very long

[Even Rouault]

Le mercredi 22 août 2012 20:13:39, Radim Blazek a écrit :
> Even,
> thanks for exhaustive explanation and testing.
> 
> On Wed, Aug 22, 2012 at 2:37 PM, Even Rouault
> 
> <even.rouault at mines-paris.org> wrote:
> >> I found in GDAL ecwdataset.cpp that it is treating  single row
> > 
> >> requests in IRasterIO in a special way:
> > I tried the following Python script that must be representative of how
> > QGIS must do picking (I guess it does a RasterIO(, .... x, y, 1, 1, ...
> > 1, 1) )
> 
> Yes.
> 
> > I suppose your workaround in QGIS will be to read 1x2 pixel or something
> > like that.
> 
> Yes, I have used 2x2.

Hum, I humbly suggest that the fix should be done in the ECW driver rather than 
in QGIS. The issue with the 2x2 workaround is that if other GDAL drivers have 
optimizations for the 1x1 pixel use case (which would be reasonable), they 
will be unused now.

> 
> Radim