The size of each entry is 44 bytes. Each entry contains eleven elements. They are all of size 4 bytes and in network byte order. Thus they can simply be read as an array of integers on big-endian systems (e.g., 68k and SPARC). On little-endian systems (e.g., x86 and VAX), their byte order must be swapped.
| Offset (bytes) |
Size (bytes) |
Type | Description |
|---|---|---|---|
| +0 | 4 | unsigned integer | UTC modified Julian day at midnight |
| +4 | 4 | unsigned integer | #ticks from midnight (10 msec) |
| +8 | 4 | booleans | Flags (see below) |
| +12 | 4 | unsigned integer | Local apparent sidereal time (10 msec) |
| +16 | 4 | unsigned integer | Requested apparent right ascension (10 msec) |
| +20 | 4 | signed integer | Requested apparent declination (100 mas) |
| +24 | 4 | signed integer | Parallactic angle (100 mas) |
| +28 | 4 | signed integer | Requested azimuth (100 mas) |
| +32 | 4 | signed integer | Requested elevation (100 mas) |
| +36 | 4 | signed integer | Error in azimuth (100 mas) |
| +40 | 4 | signed integer | Error in elevation (100 mas) |
Right ascensions, declinations and parallactic angles are not valid if the CELESTIAL flag (see below) is not set, i.e., zero.
The 32-bit flag field is defined as follows:
| Offset (bytes) |
b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 |
|---|---|---|---|---|---|---|---|---|
| +8 | TTL Input 8 |
TTL Input 7 |
TTL Input 6 |
TTL Input 5 |
TTL Input 4 |
TTL Input 3 |
TTL Input 2 |
TTL Input 1 |
| +9 | TTL Output 8 |
TTL Output 7 |
TTL Output 6 |
TTL Output 5 |
TTL Output 4 |
TTL Output 3 |
TTL Output 2 |
TTL Output 1 |
| +10 | ON-beam | Chopping | ||||||
| +11 | Tracking | Acquired | Scanning | Transited | Celestial |
The TRACKING flag in the telescope pointing information is different from the TTL TRACKING (/IDLING) signal. For historical reasons, the TTL TRACKING (/IDLING) signal is high when the TRACKING flag is true but the SCANNING flag is false.