[teqc] upcoming change to '-unhealthy' as default option

Lou Estey lou at unavco.org
Thu Nov 9 10:18:46 MST 2017


Upon overhauling some of the antenna position code in teqc (and more about
this in a future email to the list), I've discovered that the option of '+unhealthy'
(as default), added 2015 Sep 24, was not really doing what was intended.
To review (and you can go back to the on-line development log for teqc at
and search for 'health' from the 2015 Sep 24 entry forward in time during
that month), the two 'unhealthy' options, for qc, are in '+help' as:

[936] teqc +help | grep unhealthy
+unhealthy               allow use of unhealthy navigation messages if found (default)
-unhealthy               don't allow use of unhealthy navigation messages if found

The implied, but not stated, part is "allow use in orbit determination".
The idea was include an SV's ephemeris for orbit determination, by default,
whether the SV's ephemeris health flag was showing either all was well or
some state of unhealthiness.  To not use any ephemerides with unhealthy status
one would use '-unhealthy', i.e. "don't use unhealthy ephemerides" (and maybe
see https://postal.unavco.org/pipermail/teqc/2016/002076.html for reminder
of options starting with '-' or '+').

But due to a subtle logic bug in the code since Sep 2015, the default '+unhealthy'
wasn't really using orbital positions from SVs with an unhealthy status during qc.

Correcting that bug, one immediately sees that, yes, in general, one really
should be ignoring orbit information from any SV with an unhealthy status.
(Also correcting this bug explains why, back in Sept 2015 when I was testing
the original implementation, that "including" SVs with unhealthy status didn't
seem to have any negative effect on position solutions -- which was a very
counter-intuitive result, and in hindsight, a clue that there was a bug.)

With this subtle logic bug now fixed, it becomes necessary to also make the
'-unhealthy' option be the default, requiring you to use '+unhealthy', i.e.
"use unhealthy ephemerides in addition to healthy ephemerides", if you want
to include unhealthy ephemerides during the qc antenna position determination --
but you do so at your own risk of ending up with potentially strange results.

Just to be clear, you will still be able to see any SV that has an unhealthy
status in the qc's ASCII time plot, e.g. with the fixed code:

teqc +R1-26 +ap +qcq tmp.obs
  SV+---------|--------|--------|--------|--------|--------|--------|--------+ SV
  27|L+~~~~~~~~~~~~~~~~~ILL                                                 +| 27
  18|L-ccccccccccccLL_                             L^cccccccccLL            L| 18
   6|'''''''''''''''''''''                                                 ''|  6
R23|*+_                         _++******M+_             +-I***********+_   |R23
R18|'''''''''''''''                      ''''''                  '''''''''''|R18
R13|-L                   +++++                      +1-***************LIL   |R13
00:00:00.000                                                        23:59:50.000
2014 Feb 22                                                          2014 Feb 22

shows GPS PRN 6 and GLONASS slot # 18 with unhealthy status, as is also reported
a bit further down in the report with:

NAVSTAR GPS unhealthy SV:  6
     GLONASS unhealthy SV: 18

Hopefully all this makes sense after some rumination.


Louis H. Estey, Ph.D.              office:  [+001] 303-381-7456
UNAVCO, 6350 Nautilus Drive           FAX:  [+001] 303-381-7451
Boulder, CO  80301-5554            e-mail:  lou  unavco.org

"If the universe is the answer, what is the question?"
                                                -- Leon Lederman

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