Checking FT1 files in the context of the FT2 reprocessing

Maria-Elena reprocessed a complete set of files for a run for 634008661:

root://glast-test-rdr.slac.stanford.edu//glast/Data/Flight/Level1/LPA/dev/5.9/ft2/gll_pt_p310_r0634008661_v000.fit
root://glast-test-rdr.slac.stanford.edu//glast/Data/Flight/Level1/LPA/dev/5.9/ft2Seconds/gll_pt1s_p310_r0634008661_v000.fit
root://glast-test-rdr.slac.stanford.edu//glast/Data/Flight/Level1/LPA/dev/5.9/ft1/gll_ph_p305_r0634008661_v000.fit
root://glast-test-rdr.slac.stanford.edu//glast/Data/Flight/Level1/LPA/dev/5.9/ls1/gll_ev_p305_r0634008661_v000.fit

Checks on run 634008661

• Philippe: I've compared the new FT1 file with the original file root://glast-rdr.slac.stanford.edu//glast/Data/Flight/Level1/LPA/prod/5.7/ft1/gll_ph_p305_r0634008661_v000.fit and the key variables (energy, direction, event class and types) are identical. The nb of events in the files are also identical.
• Don:

  I compared the original and new photon and event files that Maria Elena created. The data in the photon (FT1) files match exactly. The event files (LS1) have small differences in the PtAlt, PtLat, and PtMagLat columns. Looking at a few examples, the differences are in the fourth significant figure or lower (e.g., 537.501 vs 537.494 in PtAlt). I assume this is because of the change to the geodetic position calculation implemented for the FT2 files. I compared PtAlt values in the LS1 file against RAD_GEO values in the FT2 file for the reprocessed run and they are consistent, so that checks out. I supposed if we were to do everything properly we would need to reprocess all the event files, too, but I think we can just document the issue and move forward since the differences are small.

Later she created a few more FT1 files for several runs:

root://glast-test-rdr.slac.stanford.edu//glast/Data/Flight/Level1/LPA/dev/5.9/ft1/gll_ph_p305_r0600163450_v000.fit
root://glast-test-rdr.slac.stanford.edu//glast/Data/Flight/Level1/LPA/dev/5.9/ft1/gll_ph_p305_r0601783627_v002.fit
root://glast-test-rdr.slac.stanford.edu//glast/Data/Flight/Level1/LPA/dev/5.9/ft1/gll_ph_p305_r0634002957_v000.fit
root://glast-test-rdr.slac.stanford.edu//glast/Data/Flight/Level1/LPA/dev/5.9/ft1/gll_ph_p305_r0633997253_v000.fit

Don: I found some differences this time.  While the 600163450 and 601783627 files are identical to the latest versions received at the FSSC,  the last two files both have differences in the column 18 (LIVETIME) values starting at rows 11859 and 20150, respectively.   For instance for 634002957

The first number is the for "old" file while second is the "new" file.  Every row after this seems to have a different value for LIVETIME.  The other run 633997253 shows the same behavior.  The fdiff utility doesn't report any other differences in the data (e.g, the number of photons in the files are the same).

According to the confluence page On FT1 Livetime: "So for now, the LIVETIME values in the FT1 files should be ignored. Again, they are not currently used by the Science Tools, and in particular do not affect calculations of exposure, which are made with the livetime accumulations in FT2 files."

Checking (RA,DEC) directions: (Philippe)

Following Seth's advice, the following plots were updated using the Haversine formula, which removed a peak at 1e-6.

The 2 runs with significant differences are the ones reported by Don with the weird LIVETIME differences.

Since the (theta,phi) values don't change, the differences occur when going from instrument to sky coordinates. But the differences are on the event basis so it doesn't look like a calibration difference between the 2 processings.

There is no correlation between the angular differences and the LIVETIME differences.

List of differences

The fact that for some events there is a difference in one of the RA,DEC variables and not in the other one is very strange.

I note that some numbers appear several times. Very weird !

And:

• 3.814697265e-06 * 2 = 7.6293945e-06
• 3.814697265e-06 * 3 = 1.5258789e-05
• 3.814697265e-06 * 8 = 3.0517578e-05

Merit files

I've compared:

• original=root://glast-rdr.slac.stanford.edu//glast/Data/Flight/Level1/LPA/prod/5.7/merit/r0634002957_v001_merit.root
• new=root://glast-test-rdr.slac.stanford.edu//glast/Data/Flight/Level1/LPA/dev/5.9/merit/r0634002957_v000_merit.root

And I see the same differences for the variable FT1Ra and FT1Dec.

Pieces of code (/nfs/farm/g/glast/u52/repomanBuild/redhat6-x86_64-64bit-gcc44/GlastRelease/20-10-04-gr07/)

The variables FT1RA and FT1Dec are filled in AnalysisNtuple/src/FT1Alg.cxx:

• gps = astro::GPS::instance();

• double etime(header→time());

• gps→time(etime);

• glastDir= Hep3Vector(CTBBestXDir, CTBBestYDir, CTBBestZDir);
  • this information is the same in both merit files
• SkyDir sdir( gps->toSky(glastDir) );
• m_ft1ra = sdir.ra();
• m_ft1dec = sdir.dec();

The gps object lives in astro/src/GPS.cxx:

• astro::SkyDir GPS::toSky(const CLHEP::Hep3Vector& latdir, double met)
  • CLHEP::Hep3Vector tdir( - (m_currentPoint.rotation() * m_alignment * latdir) );
• void GPS::update(double inputTime)
  • //this function calculates all the relevant position and orientation info
  • the differences could come from this part of the code

Plots with merit files from run 634002957: