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Here I collect the results of the testing I am performing, comparing the output generated by the old ft2Util code (written by Andrea Tramacere) with the output generated by my code (ft2Util_2).

Fake FT2

Testing procedure

I collected a bunch of Magic 7 files for a total of ~50 days of in-orbit operation. These M7 files are the one produced by L1, in their latest versions. Thus, they should be complete (without gaps). This is, in other words, the "ideal" situation. They are not contiguous, since I've taken them directly from the disk without caring for the continuity, since it shouldn't matter here.

Then I run the executables to produce the fake FT2 files (i.e., without LIVETIME), and I compared the results. Specifically, for every quantity q (like LAT_GEO, LON_GEO, RA_SCX, DEC_SCX...) I computed (qold-qnew)/qold , that is, the "fractional difference". These are the two command lines I used:

  • Old version:  
    makeFT2Entries.exe -M7File $magic7 \
                    -FT2_fits_File ${filenameroot}_andrea.fits \
                    --Gleam --test-quaternion \
                    -DigiTstart $start -DigiTstop $stop \
                    -new_tpl /afs/slac.stanford.edu/g/glast/ground/releases/volume02/ScienceToolsv9r18p5/fitsGen/v6r1p1/data/ft2.tpl
  • New version:  
    makeFT2.exe -m7file $magic7 \
            -ft2file ${filenameroot}_io.fits \
            -ft2start $start \
            -ft2stop $stop
    (without specifying a template, the new version uses the template provided by the current version of fitsGen)

The following plots show the results (mind the scales on the y axes, usually the differences are very small!):

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As you can see, there are differences, but they are very small.

The maximum difference is of the order of ~ 2%, and it is in QSJ_3. QSJ_3 is the Z component of the vectorial part of the attitude quaternion. Usually the attitude quaternion is taken directly from the ATT message in the Magic 7 file. Those messages are issued by the spacecraft 5 times per second. Anyway, there are cases when there is no ATT message corresponding to a particular time interval, thus the codes have to interpolate (or extrapolate). This usually can happen at the very beginning of a run, or because of gaps in the Magic 7 file. The differences between the two codes arises mainly from two different strategies adopted for the interpolation/extrapolation: the old code uses only ATT messages arriving in sync with an ORB message (that is, one time per second), discarding the others; the new code, instead, uses all the available ATT messages. Thus, the new code should provide better interpolation/extrapolation. Anyway, the differences are really small, and I can't think of any application where they could really matter... 

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