[QGIS-trac] [Quantum GIS] #1574: Displaying ECW raster images is very slow

[Quantum GIS]

#1574: Displaying ECW raster images is very slow
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   Reporter:  trapanator                        |              Owner:  warmerdam
       Type:  bug                               |             Status:  new      
   Priority:  major: does not work as expected  |          Milestone:           
  Component:  Rasters                           |            Version:  1.0.0    
   Keywords:  ECW Raster                        |   Platform_version:  1.0.1    
   Platform:  Windows                           |           Must_fix:  No       
Status_info:  0                                 |  
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 Hi,

 I have QGIS 1.0.1 for windows installed from OSGEO4W.

 If I try to open a simple ECW (67 MB), QGIS is taking too long to open it
 (about 30-40 seconds). It seems that it doesn't use overviews anymore.

 '''Warmerdam''' says from OSGEO4W mailing list:


 {{{
 The ECW driver does not report having any specific overview levels
 and this defeats certain optimizations in the statistics computation.
 I believe this has a bad effect when an ecw layer is first added to
 qgis but browsing after that should be fast.

 The fix is to make the histogram computing logic smarter
 (I'm not positive if QGIS is using it's own or GDAL's logic)
 so that for formats like ECW with "arbitrary overviews" a
 small overview sample of data will be fetched for statistics.

 I believe this issue is the same in all modern QGIS+GDAL
 builds, not just specifically in OSGeo4W or windows.
 }}}

-- 
Ticket URL: <https://trac.osgeo.org/qgis/ticket/1574>
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Quantum GIS is an Open Source GIS viewer/editor supporting OGR, PostGIS, and GRASS formats