ECW -- ERDAS Compress Wavelets (.ecw)

GDAL supports .ecw format for read access and write. The current implementation reads any number of bands but returns only as eight bit image data. Coordinate system and georeferencing transformations are read, but in some cases coordinate systems may not translate.

Support for the ECW driver in GDAL is optional, and requires linking in external ECW SDK libraries provided by ERDAS.

Creation Issues

The ECW 4.x SDK from ERDAS is only free for image decompression. To compress images it is necessary to build with the read/write SDK and to provide an OEM licensing key at runtime which may be purchased from ERDAS.

For those still using the ECW 3.3 SDK, images less than 500MB may be compressed for free, while larger images require licensing from ERDAS. See the licensing agreement and the LARGE_OK option.

Files to be compressed into ECW format must also be at least 128x128. ECW currently only supports 8 bits per channel.

When writing coordinate system information to ECW files, many less common coordinate systems are not mapped properly. If you know the ECW name for the coordinate system you can force it to be set at creation time with the PROJ and DATUM creation options.

Creation Options:

ECW format does not support creation of overviews since the ECW format is already considered to be optimized for "arbitrary overviews".

Configuration Options

The ERDAS ECW SDK supports a variety of runtime configuration options to control various features. Most of these are exposed as GDAL configuration options. See the ECW SDK documentation for full details on the meaning of these options.

See Also: