Please use the current specification instead for creating new files.
The header consists of the following:
Byte Offset Length Contents Description 0 6 "vf1.1" A marker which indicates that this is a VF file 6 1 UTM Flag which indicates whether projection is UTM (true) or Geographic (false) 7 4 (int) UTM zone Indicates the UTM zone (1-60) if the file is in UTM. Negative zone numbers are used for the southern hemisphere. 11 4 (int) Datum Indicates the Datum, see the BT format for the values used. 15 4 (int) Count The number of plant instances in this file.
After the header there are Count plant instances, each composed of the following fields:
Byte Offset Length Contents Description 0 8 (double) X coordinate 8 8 (double) Y coordinate 16 4 (float) Height This is the full extent, in meters, from the ground to the top of the plant. Visualization software can be expected to imply other attributes, such as width and age, from this value. 20 2 (short) Species An ID for the species. This should correspond with the ID of the species in your species.xml file. 22 2 Padding Room for future expansion.
It would be better to use an absolute enumeration for species. The current approach of using the ID in the species.xml is usable for individual projects, but not good for interchange of datasets between users. Unfortunately, there does not seem to be a numbering system for species. There is only the scientific naming system, Genus species, which is relatively reliable and distinct, but requires a long (and variable-length) string to identify. In fact, there is not yet even a database of all scientific species names, although there are efforts such as SPECIES 2000 and the World Biodiversity Database.
One possibility might be to add an additional table to the VF file, which defines, after the header, the IDs with their scientific names, on a per-file basis. Since the number of species in a single file is generally small in relation to the number of instances, the increase and size and complexity would be modest, and retain the efficient representation of species per instance.