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 Intergraph (previously ERDAS).

In addition to ECW files, this driver also supports access to network image services using the "ECWP" protocol. Use the full ecwp:// url of the service as the dataset name. When built with SDK 4.1 or newer it is also possible to take advantage of RFC 24 style asynchronous access to ECWP services.

Starting with GDAL 1.9.0, XMP metadata can be extracted from JPEG2000 files, and will be stored as XML raw content in the xml:XMP metadata domain.

ECW metadata domain / Georeferencing update

(Starting with GDAL 1.9.0)

The PROJ, DATUM and UNITS found in the ECW header are reported in the ECW metadata domain. They can also be set with the SetMetadataItem() method, in order to update the header information of an existing ECW file, opened in update mode, without modifying the imagery.

The geotransform and projection can also be modified with the SetGeoTransform() and SetProjection() methods. If the projection is set with SetProjection() and the PROJ, DATUM or UNITS with SetMetadataItem(), the later values will override the values built from the projection string.

ECW Version 3 Files

(Starting with GDAL 1.10.0)

ECW 5.x SDK provides amended file format which allows to store data statistics, histograms, metadata, rpc metadata and supports UInt16 as band data type. Currently not everything is implemented:

File Metadata Keys:

Following Header Metadata will be reported:

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 for ECW Version 2 files. ECW Version 3 files supports 16 bits per channel (as Uint16 data type). Please see Creation options to enable ECW V3 files writing

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: