Derive_SPD performs a number of intermediate tasks on ERD in order to prepare an observation's data for the scientific analysis performed by AAC in the pipeline. In conjunction with the pointing files, SPD is also the recommended starting point for other analysis systems, including CIA, as it contains all the ISOCAM information necessary for most astronomical requirements.
Derive_SPD makes one CISP or CPSP row for every pair of EOI and RESET CIER or CPER records, unless subtraction was already performed on board. The imaging data are accompanied by RESET data, where available; 15 columns of image-description data, such as the various wheel settings; 3 types of image statistics; and the most important temperature, bias-voltage and blackbody housekeeping data. Given the importance of the CAM SPD, the contents of the CISP[1].TABLE are shown in Table 5.5.1.
The CISPDISC discrepancy
flags have bits set to show any differences between the record's optical
configuration as defined by its instrument settings and the commanded
values from the Compact Status that sometimes occur because of the time
it takes for the wheels to move. While it is possible to interrogate
individual bits, the recommendation to use only data with CISPDISC=0 is
followed by the pipeline.
Similarly, CISPQFLG=7 shows a record with QLA, OTF and OTFSUM flags all set
although the user may choose to ignore the zero
order QLA
stabilisation flag during transient modelling.
It is, of course, necessary to use appropriate calibration data during analysis dependent on the instrument configuration which often changes during the course of an observation. These instrument changes are reflected in a set of CISP[1].HEADER keywords including some that were originally designed to give recommendations of which calibration data should be used. However, the proper calibration selection scheme is more complicated than allowed by the CISP[1].HEADER scheme and users should ignore them and follow instead the advices provided in Chapter 6.
| column | type | description |
| GPSCTKEY | 1J | Instrument time key |
| GPSCRPID | 2B | Raster point ID |
| CISPBOOT | 1J | Time since processor's boot [CAMTU] |
| CISPDEID | 1B | Detector ID (SW:0, LW:1) |
| CISPCNFG | 1B | Configuration number within AOT |
| CISPQFLG | 1B | CAM's QLA flag: F2_QLA +  OTFLAG + 
OTFSUM |
| CISPPROC | 1B | PROCessing mode 0:Normal, 1:Accumulated, 2:Sampled |
| CISPDISC | 1I | CSH/ERD `Discrepancy Flags' |
| CISPPFOV | 1I | Lens wheel step number |
| CISPITIM | 1I | Elementary integration time (CAMTU) |
| CISPFCVF | 1I | Filter wheel step number |
| CISPWAVE | 1E | Filter or CVF central wavelength |
| CISPEWHL | 1I | Entrance wheel step number |
| CISPSWHL | 1I | Selection wheel step number |
| CISPWDTH | 1I | Filter/CVF width in millimicrons |
| CISPOBST | 1B | Current op-mode 1:OBS, 2:DRK, 3:CAL, 4:CLN, 0:IDLE |
| CISPCVFS | 1B | CVF scan on/off (1/0) |
| CISPTEMP | 10E | CAM temperatures [K] |
| CISPBLKB | 2E | Black body current & voltage |
| CISPGAIN | 1B | Electronics gain (0, 1, 2) |
| CISPOFFS | 1B | Electronics offset (0...3) |
| CISPBSFG | 1I | Beams flag:  C+R; C:cycle, R:ref#, Add 16 on Ref# |
| CISPMEAN | 1E | Frame mean of CISPDATA (this - last) |
| CISPMEDI | 1E | Frame median of CISPDATA (this) |
| CISPSRMS | 1E | Frame rms of CISPDATA (this - last) |
| CISPICNT | 1I | Current internal image counter |
| CISPACSA | 1B | ACcumulated/SAmpled image register |
| CISPAOBS | 1B | F2_AOT_AOT +  F2_AOT_OBS |
| CISPBIAS | 10E | Bias voltages |
| CISPDATA | 1024I | Detector data (EOI RESET) |
| CISPRESE | 1122I | RESET level for NORMAL processing |
| CISP3334 | 64I | Columns 33 & 34 of SW readout |