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.
Three tags contain scalar data:
ModelTiepointTag = 33922 (0x8482) ModelPixelScaleTag = 33550 (0x830E) ModelTransformationTag = 33920 (0x8480)
Three tags store additional values, called "GeoKeys":
GeoKeyDirectoryTag = 34375 (0x87AF) This tag will store the all the keys and the SHORT values GeoDoubleParamsTag: 34736 (0x87B0) This tag will store the DOUBLE values GeoAsciiParamsTag: 34737 (0x87B1) This tag will store the ASCII values.
There are 65536 possible GeoKeys.
The GeoTIFF spec 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. |
| 3071..4095 | Projected CS Parameter keys. |
| 4096..5119 | Vertical CS Parameter keys. |
| 5120..32767 | Reserved. |
| 32768..65535 | Private use -- use to store your own data. |
Enumerate GeoKeys in an existing file by using EnumGeoKeys.
Read a specific GeoKey by using ReadGeoKey.
Use the GeoKeys property to prepare GeoKeys for file writing or saving. These GeoKeys are maintained as a per-thread array of GeoKeys.You can write the GeoKeys in two ways:
When saving a new image as GeoTif , with one of the Save methods. You can update an existing file, using WriteGeoKeys.
Note: To save a region inside a TIFF file, you must have an unlocked Document, Vector, or Medical Imaging license.
For more information on the GeoTIFF tags and for the complete list of the predefined GeoKeys values, refer to the GeoTIFF specifications found at
http://www.remotesensing.org/geotiff/geotiff.
GeoTIFF files also support standard TIFF comments and tags. For more information on standard TIFF tags and comments, see Implementing TIFF Comments and Tags.