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FITS Headers
The software maintains two FITS keyword databases, one for user keys and a second for system keys. The user keyword database is manipulated with the key command. System keys are maintained by the server and cannot be modified by the user.
Although system keys cannot be directly modified or deleted, if a user key has the same name as a system key, the user takes precedence and will become the key/value used in the FITS header.
The server writes the system keywords shown in Table 2.
Table 2. Automatically-generated primary FITS HDU keywords
| KEY | VALUE, Type, or Format | Comment |
|---|---|---|
| SIMPLE | T | file does conform to FITS standard |
| BITPIX | (INT) | number of bits per data pixel |
| NAXIS | (INT) | number of data axes |
| NAXIS1 | (INT) | length of data axis1 |
| NAXIS2 | (INT) | length of data axis2 |
| EXTEND | T | F | FITS dataset may contain extensions |
| CAMD_VER | Mmm dd YYYY HH:MM:SS | camerad server build date and time |
| FILENAME | (STRING) | this filename |
| EXPTIME | (INT) | exposure time in <unit> (see §4.3.29) |
| TM_ZONE | T | F | time zone, "local" or "GMT" (see §3.2.1) |
| SHUTTEN | T | F | shutter was enabled |
| SHUTFORC | 0 | 1 | shutter force level, {0|1} for {closed|open}. only present when shutter has been forced. See §4.3.38 |
| GAIN_nn_ | (INT) | gain for AD channel nn. Archon-only. |
| OFFSET_nn_ | (INT) | offset for AD channel nn. Archon-only. |
For multi-extension data cubes, each extension's header will contain the keywords shown in Table 3.
Table . Automatically-generated secondary FITS HDU keywords
| KEY | VALUE | Comment |
|---|---|---|
| XTENSION | IMAGE | file does conform to FITS standard |
| BITPIX | (INT) | number of bits per data pixel |
| NAXIS | (INT) | number of data axes |
| NAXIS1 | (INT) | length of data axis1 |
| NAXIS2 | (INT) | length of data axis2 |
| PCOUNT | required | |
| GCOUNT | required | |
| EXTNAME | (STRING) | "name" of the extension is the extension number {1,2,3,...} |
| HDUVERS | version of format | |
| DETSIZE | CCD size (pixels) | |
| CCDSEC | detector section | |
| ROISEC | region of interest | |
| AMPSEC | amplifier section | |
| TRIMSEC | trim section | |
| DATASEC | data section | |
| BIASSEC | bias section | |
| DETSEC | detector section |
The writekeys command controls when the FITS header keywords are written.