The module eng2phys reads the contents of a given raw LECS HK file
(type _rhk) from which it creates a new "physical" HK file
(type _hkp). The structure of the input and output files is
identical with respect to the number of Bintable extensions and number
of columns in each extension, the data, however, have been manipulated in
the following manner:
- All HK parameter values in the 2nd Bintable extension have been scaled
from digital (engineering) to physical units (e.g., digital temperature
units to "degree Celsius", digital pressure values to "mbar", etc.).
- The attitude data in the 3rd Bintable extension have been
filtered according to a selection criterion which involves
the deviation of the pointing from the median pointing position
calculated from the entire data set. In more detail, an
attitude data record #i is eliminated if it represents a
spacecraft attitude for which the pointing deviates from
the nominal pointing direction by more than a certain threshold value.
This threshold is an alterable input parameter
pntfluct with a d/f value
of 3 arcmins (cone opening angle).
This step 2 has proven to be necessary to eliminate spurious "spikes" in
the attitude data which are occasionally present due to a problem in the FOT
production software.
As a result of the unit conversion in step 1, the type of certain columns of
the second Bintable extension in the input and output file is different, i.e.,
has changed from "I" (16-bit integer) to "E" (32-bit floating point). For
more details and a list of affected columns please consult Sect. 2.5.1 in
[1].
The attitude data filtering has naturally decreased the
number of rows in the ASPECT extension, thereby creating
gaps in the data. Given the fact that potential "spikes" in the
attitude data are due to at most one or two erroneous records, the
generated gaps should not be larger than 2s (nominal attitude data
granularity is 0.5s). A gap of this size is insignificant for all
SAXDAS modules which access the attitude data.
Please note: The contents of both types of HK files (rhk.fits and
hkp.fits) can be inspected with the
hkplot task.