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XMM-Newton Science Analysis System Page: 1
atthkgen
November 22, 2004
Abstract
The task atthkgen produces a FITS le with a single bintable extension, con-
taining the entire attitude information for a complete observation.
1 Instruments/Modes
Instrument Mode
EPIC MOS all
EPIC PN all
RGS all
OM all
2 Use
pipeline processing yes
interactive analysis yes
3 Description
We need to be able to make use of OM and AOCS attitude information to create GTIs. These GTIs may
be based upon the presence of AOCS or OM data, the quality of these data, osets of the attitude data
from the average pointing, or dierences between the AHF and OM data.
The task atthkgen produces a FITS le with a single bintable extension containing the entire attitude
information for a complete observation, by accessing the particular ODF in question. The task tabgtigen
can then be used to create GTIs from this le.
Once the whereabouts of the particular ODF in question are known, (set via the environment vari-
able $SAS ODF) the observation start and end times are read in by atthkgen via an OAL call. The
task atthkgen then loops through every second, say (or whatever the user denes via the parameter
timestep), of the observation, obtaining the attitude information and quality for this time. The task
accesses the attitude data from both the Attitude History File (AHF) and from the OM Tracking History
Data les (THF).
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The attitude information at the requested point in time is computed by an OAL call. If the closest AHF
or OM THF points lie further than 20 seconds away from the requested point in time, the attitude quality
is deemed bad and the RA, Dec and position angle are set by the OAL call to bad.
The le will contain (per second, say) the following columns: rstly, along with the time (column name
TIME), the AHF and OM attitude information (i.e. RA, Dec, position angle - AHFRA, AHFDEC, AHFPA, and
OMRA, OMDEC, OMPA). Here, NULL values (i.e. `INDEF' in eld) in all three elds will indicate that the
quality is bad, hence quality ltering can be done by tabgtigen (by searching for these NULL values)
to create attitude quality GTI les. If the attitude quality is good, then the absolute pointing dierence
between the AHF instantaneous star-tracker pointing and the previously calculated median value of
the star-tracker pointing is given as DAHFPNT. Similarly the OM equivalent (DOMPNT) is given and the
dierence between the AHF and OM pointings (DAHFOM) (in the cases where the quality is bad, NULL
values (`INDEF') are given).
Also included as attributes in the primary header will be the mean and median values of the nine tabulated
attitude columns. These will be named AAHFRA, AAHFDEC etc (the `A' indicating average [i.e. mean]) and
MAHFRA, MAHFDEC etc (the `M' indicating median). These values can be accessed by the task attcalc.
4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
atthkset yes lename atthk.dat none
output ts le name
timestep yes real 1.0 >0.0 s
Duration (in sec) of `step' through attitude information (output le entries are separated by this dura-
tion)
5 Errors
This section documents warnings and errors generated by this task (if any). Note that warnings and
errors can also be generated in the SAS infrastructure libraries, in which case they would not be docu-
mented here. Refer to the index of all errors and warnings available in the HTML version of the SAS
documentation.
badTimestep (error)
Parameter timestep should be greater than zero
BadAhfAttitude (warning)
No good AHF attitude found
corrective action: Continue, with warning message
BadOmAttitude (warning)
No good OM attitude found
corrective action: Continue, with warning message
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BadAhfOmAttitude (warning)
No good simultaneous AHF and OM attitude found
corrective action: Continue, with warning message
6 Input Files
1. Attitude History File and one or more of the OM Tracking History Data les held within
the specied ODF
7 Output Files
1. FITS le with a single bintable extension (ATTHK), containing the entire attitude information
for the complete observation. The le will contain, along with the time (TIME), the AHF and
OM attitude information (i.e. RA, Dec, position angle - AHFRA, AHFDEC, AHFPA, OMRA, OMDEC,
OMPA), with NULL (`INDEF') values in all three elds indicating bad attitude quality. If the
attitude quality is good, then the absolute pointing dierences between the instantaneous
AHF and the median AHF star-tracker pointing (DAHFPNT), between the instantaneous OM
and the median OM THF pointing (DOMPNT), and between the AHF and OM pointings
(DAHFOM) are also given (NULL (`INDEF') values will be given in the bad quality cases).
All columns are of type real64, and all, except TIME (in sec) are given in units of degrees.
Attributes in the primary header give the mean and median values of the nine tabulated
attitude columns. They are named as the columns prexed by an `A' for average (i.e. mean)
and an `M' for median. Keywords written to le: TELESCOP DETNAM FILTER OBS ID OBS MODE
ORIGIN DATE-OBS DATE-END RA OBJ DEC OBJ RA NOM DEC NOM AAHFRA AAHFDEC AAHFPA AOMRA
AOMDEC AOMPA ADAHFPNT ADOMPNT ADAHFOM MAHFRA MAHFDEC MAHFPA MOMRA MOMDEC MOMPA
MDAHFPNT MDOMPNT MDAHFOM NATT NGAHF NGOM NGAHFOM
8 Algorithm
subroutine atthkgen
* get ODF
* get start and end times of complete observation
* open output fits file
* loop through time (timestep)
set attitudeFromAhf to true + call OAL_getAttitude (get AHF attitude)
set AHF info to OAL_getAttitude info (or to NULL if bad)
calculate summed attitude information for AHF
set attitudeFromAhf to false + call OAL_getAttitude (get OM attitude)
set OM info to OAL_getAttitude info (or to NULL if bad)
calculate summed attitude information for AHF OM
calculate AHF-Om difference
* end loop through time
* get median infomation at correct point in loop (AHF/OM values)
* calculate mean attitude information (AHF/OM)
* loop through time (timestep)
calculate differences (AHF-PNT, OM-PNT)
* end loop through time
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* get median infomation at correct point in loop (Diff PNT values)
* calculate mean attitude information (Diff PNT)
* fill fits file columns (AHF, OM)
* fill in differences columns
* add keywords, means, medians and history to fits file
end subroutine atthkgen
9 Comments
The OM Tracking History Files give only relative displacements as attitude information,
and how this will be translated into absolute RA and Dec is still uncertain. Perhaps in the
future it could be done via the task omatt in conjunction with OAL getAttitude though
this is still unknown, and may imply that a large fraction of the OM pipeline may need to
be run early in the PPS.
It is thought, at the moment, that the AHF may only have a very few number of entries in
it, and as such, atthkgen may seem not well suited to such a situation. Note though that
it is envisaged that the movement oset threshold at which new AHF entries will be input
may be reduced from 2.5 arcsec to 0.5 arcsec. This will give many more AHF entries.
If GTIs are to be produced from this le, then it may be important that the output be an
additional PPS product. If however, the le is easily and quickly recreatable by the user
(e.g. so long as the OM chain does not have to be re-run, for instance), then it may not
need to be a product.
This le is needed as input for the attcalc task, where the mean/median attitude values
are taken as the PNT attributes.
10 Future developments
As discussed above, we are still unsure as to how the absolute OM pointing information will be obtained.
11 Examples
atthkgen (full attitude information in ODF [set via the environment variable $SAS ODF]
entered every second into le atthk.dat)
atthkgen atthkset=newatthk.dat timestep=10 (full attitude information in ODF entered every
10 seconds into le newatthk.dat)
References
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