ISOCAM Interactive Analysis User's Manual Version 5.0 - ISO - ESA

222 CHAPTER 19. ADVANCED SLICING
19.6.4.1 TDF files types
Here it becomes a bit tricky. . . the CAM microprocessor is of the 680x0 family. Its internal
coding of integers follow the IEEE convention: the most significant byte is the first. Telemetry
is received at VilSpa ESA Station and processed on VAX computers. These, like all based on
Intel microprocessor follow the opposite convention: the least significant byte is the first. . . A lot
of byte swapping is therefore done. Two kinds of TDF files are created – they are distinguished
by their extension.
• LTDF files are sequential files (.LTDF).
• TDFG files are indexed files (.TDFG).
All CAM slicers work on LTDF files. If you feed them with a TDFG file, it will be converted
into the LTDF format first (without you being told about).This operation can last some time. . .
19.6.4.2 Loading TDF
TDF files are very big files, normally covering a whole orbit. It may be a challenge for your
computer just to load the entire file. Therefore it is better to select a part of a telemetry file
rather than the whole. Three keys may be used for this, in order to pick the interesting part of
the TDF: they are UTK, ITK and FMT.
• UTK stands for Uniform Time Key: its value is the number of 1/24 s that have passed
since the 1 November 1995 at 0h00. Its value is updated every image in the TDF (F2
format).
• ITK stands for Instrument Time Key: its value is the number of CAMTU or CAM Time
Unit (roughly 0.14 s) that have passed since the 1 November 1995 at 0h00. Its value is
updated every image in the TDF (F2 format)
• FMT stands for TDF FORMAT. Its value is the number of TDF formats (one every 2
seconds) sent since the 16 November 1995 18h36. It is of course updated every TDF
format.
See the ISO Data Product Document, Appendix B, for additional information on these keys.
19.6.4.3 Slicing TDF
Taken all that has been said in the last two subsections into account, slicing TDF files is just
the same as slicing ERD files. Remember that you cannot use any coordinate information like
IIPH, or ORBIT. It is also impossible to check the contents of a TDF versus the commanded
position.
19.6.5 Selecting slicing variables
The problem of selecting slicing variables has been widely addressed in Section 12.3, but since
it is one of the most important things that the user has to do when using x slicer, wewishto
recall some points here. First of all, Table 19.6.5 gives the complete list of the slicing variables
that can be used with x slicer. In order to avoid confusion, the official names of variables in
the telemetry files, in SCDs and DSD, are also given.
Let us now discuss some of these variables.