[gdal-dev] ECW reading is taking too much time

[Jorge Arévalo]

Hello, 

I'm having problems reading a ECW file with GDAL. It's taking several hours to get an equivalent GeoTIFF file, executing gdal_translate. Besides, the ECW file is 1.9GB and the resulting GeoTIFF is 21GB. The CPU is at almost 80% during the read operation. Same problem trying to load it in PostGIS Raster. The SQL file creation takes hours. 

This is the gdalinfo output

Driver: ECW/ERDAS Compressed Wavelets (SDK 3.x)
Files: PNOA_MR_OF_ETRS89_HU29_h50_0223.ecw
Size is 110680, 74840
Coordinate System is `'
Origin = (511960.000000000000000,4686950.000000000000000)
Pixel Size = (0.250000000000000,-0.250000000000000)
Metadata:
COLORSPACE=RGB
COMPRESSION_RATE_TARGET=10
VERSION=2
Corner Coordinates:
Upper Left ( 511960.000, 4686950.000) 
Lower Left ( 511960.000, 4668240.000) 
Upper Right ( 539630.000, 4686950.000) 
Lower Right ( 539630.000, 4668240.000) 
Center ( 525795.000, 4677595.000) 
Band 1 Block=256x256 Type=Byte, ColorInterp=Red
Description = Red
Overviews: 55340x37420, 27670x18710, 13835x9355, 6917x4677, 3458x2338, 1729x1169, 864x584, 432x292, 216x146
Band 2 Block=256x256 Type=Byte, ColorInterp=Green
Description = Green
Overviews: 55340x37420, 27670x18710, 13835x9355, 6917x4677, 3458x2338, 1729x1169, 864x584, 432x292, 216x146
Band 3 Block=256x256 Type=Byte, ColorInterp=Blue
Description = Blue
Overviews: 55340x37420, 27670x18710, 13835x9355, 6917x4677, 3458x2338, 1729x1169, 864x584, 432x292, 216x146

I don't know why there isn't srid information, but it should be epsg:2158

I guess the speed depends on the reading strategy (looking at debug messages, looks like the driver is reading line by line), and you may get better performance combining ECW specific options with GDAL general options.

I'm using GDAL 1.10 and ECW 3.3. I've read about a known bug with ECW 3.3 and machines with more than 8GB RAM (http://osgeo-org.1560.x6.nabble.com/Re-Qgis-developer-Large-raster-ecw-identify-very-long-td4996966.html), but it's not my case.

Is there any know strategy to make the ECW driver reading faster? I'm just executing these operations:

- For the GeoTiff transformation: 

gdal_translate -a_srs epsg:2158 PNOA_MR_OF_ETRS89_HU29_h50_0223.ecw PNOA_MR_OF_ETRS89_HU29_h50_0223.tif

- For the PostGIS Raster loading:

raster2pgsql -s epsg:2158 -t 15x15 -I -M -C -Y PNOA_MR_OF_ETRS89_HU29_h50_0223.ecw > output.sql (I've tried with different tile sizes, with the same result)

Any clues?

Many thanks in advance, 

-- 
Jorge Arevalo
Freelance developer

http://www.krop.com/jorgearevalo
http://about.me/jorgeas80

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