[Qgis-user] Re: QGIS 1.5 Update for ECW/SID support crashes

[MORREALE Jean Roc]

Le 18/10/2010 16:04, Jean-Claude Repetto a écrit :
> Le 18/10/2010 15:59, MORREALE Jean Roc a écrit :
>> Le 18/10/2010 15:53, Jean-Claude Repetto a écrit :
>>>
>>> Not only disk size is a problem, but also speed, for example when you
>>> want to display the maps at very low zoom levels.
>>>
>>> Jean-Claude
>>
>> Make tiles out of the file so just the corresponding tiles get loaded.
>
> Maybe tiling is a solution when you want to get only a small part of the
> map at zoom level 1, but if you want to display the map at zoom level
> 1/256 you have to read 65536 tiles to display only one tile.
> I have compared GeoTiff (tiled) and ECW, and ECW is MUCH faster at low
> zoom levels.

A solution I use daily on big datasets -> tiles+vrt+pyramids

Nobody is denying that a wavelet format supporting data streams is 
better than a flat file in some cases, the point here is to know if an 
old gdal version should still be used by every osgeo4w users when the 
newer brings lots of features just because of ERDAS's politic.