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

[haubourg]

Radim Blazek-2 wrote
> 
> 
> QGIS is using GDALRasterIO() which reads a single pixel on original
> resolution. AFAIK, ECW is using tiles internally so it should be all
> very fast. I can imagine 2 problems:
> 
> - the tiles in ECW file are too big - can you verify somehow how big
> are the tiles?
> 
> 
Hi Radim, I'm not ecw specialist, but I understand it is a wavelet
compression algorithm, not  a tiled one. 
There is one big image with pyramids inside. 


Radim Blazek-2 wrote
> 
> - GDAL is reading bigger portion of data than necessary (cc to GDAL list)
> 
> Is it drawing of the raster also so slow (on raster resolution zoom)?
> 
> Radim
> 
> 
No everything is fine when drawing data, whatever resolution I use, this is
the big thing with ecw.  
I must say I find that it was a bit faster with 1.7.4 than 1.8 and later.
But this could be related to other factors like internal network
capacities.. I haven't benched on it yet. 






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