Implementing GeoKeys (GeoTIFF tags)

image\sqrblit.gif 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.

image\sqrblit.gifThree tags contain scalar data:

image\sqrblit.gifThree tags store additional values, called "GeoKeys":

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

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.

image\sqrblit.gif To read a particular GeoKey from a file, use LFile::ReadGeoKey.

image\sqrblit.gif To enumerate the GeoKeys from an existing file, use LFile::EnumGeoKeys. For each GeoKey enumerated, LFile::EnumGeoKeysCallBack is called.

image\sqrblit.gif 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.

image\sqrblit.gif 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  Document, Vector, or Medical Imaging license.

For more information, refer to:

About GeoTIFF tags, Predefined GeoKey values, and GeoTIFF Specifications
(http://www.remotesensing.org/geotiff/geotiff.html)

Implementing TIFF Comments and Tags