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Implementing GeoKeys (GeoTIFF tags)

GeoTIFF files support standard TIFF comments and tags, but also contain six additional data tags describing the image location, scale, projection, and other information useful for topographic applications.

There are 65536 possible GeoKey values. The GeoTIFF specification recommends the following ranges (domains) for GeoTIFF data:

Range	Description
0..1023	Do not use; reserved for future use.
1024..2047	GeoTIFF configuration keys.
2048..3071	Geographic/Geocentric CS Parameter Keys.
3072..4095	Projected CS Parameter Keys.
4096..5119	Vertical CS Parameter keys.
5120..32767	Reserved.
32768..65535	Private - use to store your own data.

To read a particular GeoKey from a file, use LFile::ReadGeoKey.
To read all the TIFF GeoKeys from a file, use LFile::ReadGeoKeys.
To enumerate the GeoKeys from an existing file, use LFile::EnumGeoKeys. For each GeoKey enumerated, LFile::EnumGeoKeysCallBack is called.
To set GeoKeys in preparation for writing or saving, use LFile::SetGeoKey. These GeoKeys are maintained as a per-thread array. Use LFile::GetGeoKey to obtain the list of GeoKeys that have been set.
To free the data allocated by calling the LFile::ReadGeoKeys function, use LFile::FreeTags.
Write GeoKeys in one of two ways:

1. When saving a new image as FILE_GEOTIFF with a save function, such as: LFile::SaveFile, LFile::Save.

2. By updating an existing file using LFile::WriteGeoKey or LFile::WriteMetaData.

NOTE: To save a region* inside a TIFF file, you must have an unlocked Vector, Document, or Medical Imaging license.

* Regions are not supported on Windows CE.

For more information, refer to:

Search https://trac.osgeo.org/geotiff/ for GeoTIFF tags, Predefined GeoKey values, and GeoTIFF Specifications.

Topics

Implementing TIFF Comments and Tags

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