[teqc] helpful tip of week 1960

Lou Estey lou at unavco.org
Fri Aug 4 13:49:37 MDT 2017

This week's tip: when the '-week' option is very wrong to use

The 'tip of week 1904', http://postal.unavco.org/pipermail/teqc/2016/002117.html,
covered why you shouldn't use the '-week' option unless you really need to.  Apparently
this message hasn't become 100% clear yet, so in this tip I'm going to show you a case
that recently happened, and show how using '-week' when it wasn't necessary led the wrong
result.  Spoiler: the input data was technically ok, but what was in the files was
not what the filenames suggested.

The user in question was using teqc to translate a raw format into RINEX.  The raw
data filenames from a site (supplied by another operator) were named things like
<4charID>201706260000<suffix>, where '201706260000' is specifying the start time of
the data in year, month, day of month, hour, minute notation ... the way you might
expect.  And, yes, the data files actually contained the data for the period suggested
by the filename.

Further, the teqc user has a script which constructs the start time and end time of
the data from the filename and then always uses the '-st' and '-e' options (see
'tip of week 1919' http://postal.unavco.org/pipermail/teqc/2016/002159.html) with
those constructed times, like this:

teqc +obs good.obs +nav good.gps,good.glo -st 20170626000000 -e 20170626235959 <4charID>201706260000<suffix>

... and when doing this, all worked as expected:
  1) the RINEX files, good.obs, good.gps, and good.glo, were all populated and
     contained correct observation data and navigation messages for 2017 June 26.

Whether or not the following part was an experiment or part of the user's operational
script, I don't know, but, either way, including '-week 1955' (which is the GPS week
for 2017 June 26):

teqc -week 1955 +obs bad.obs +nav bad.gps,bad.glo -st 20170626000000 -e 20170626235959 <4charID>201706260000<suffix>

... did _not_ work as expected:
  1) the RINEX observation file, bad.obs, contained the wrong data, and
  2) both the GPS and GLONASS navigation files, bad.gps and bad.glo, were empty.

Is teqc at fault?  No.  So what's the problem?  The problem is that the supplier of
the data files was -- for whatever reason -- including at the start of these files
data from an entirely different earlier GPS week (= 1694).  (In fact, it was far
stranger than that: the initial 99% of the files were from the same calendar week as
the current day, but had data going back in time N years.  The data records were put
together in the file in time sequential order, however, as though smaller data files
had been UNIX `cat`-ed together in time order with the current data file being last.)
And apparently in the earlier years, navigation messages were not being recorded by
the receiver in the output format, which is why bad.gps and bad.glo were empty.

When '-week 1955' was _not_ used, teqc was forced to figure out when the data had
occurred and did so correctly because in this particular format the GPS week is
present for each epoch of data.  Because the early part of the file was for data prior
to 2017-06-26T00:00:00, teqc would skip the early data until it arrived at data for
2017-06-26T00:00:00 and then start reading and translating to RINEX.  Then the correct
and expected results were obtained.

When '-week 1955' _was_ used: You are saying to teqc: "Ignore the week value that you find
in the data.  I know better.  The data is from week 1955."  And then teqc goes: Great, ok,
the initial data records that say they are from week 1694 are not from week 1694, but
instead are for week 1955.  Teqc then proceeds to translate the initial data as though it
is from week 1955 (which it isn't) and this results in the bad.obs, bad.gps, and bad.glo
RINEX files -- which are not at all useful.

The lesson: it is very bad to lie to teqc about the GPS week at the start of the file,
whether that lie is intentional or not.

And, as stated in the earlier 'tip of week 1904', you really do not want to use the
'-week' option unless you absolutely have to.

Further, if you get the wrong data when you use '-week' with the week value you think
you should be using, whereas not using '-week' gives what you expect, then you need to
start looking at what is at the beginning of your input because, as this situation
indicates, there is something at the beginning of the input that should not be there.

I'll also remind everyone, again, that trying to use '-week' to alter the date of RINEX
files when reading RINEX does not work; '-week' information is ignored when reading RINEX.

Happy teqc-ing!


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

Past helpful tips:

week 1894: using teqc config files - http://postal.unavco.org/pipermail/teqc/2016/002067.html
week 1895: qc of high-rate data - http://postal.unavco.org/pipermail/teqc/2016/002071.html
week 1896: UNIX/Linux shells for Windows - http://postal.unavco.org/pipermail/teqc/2016/002072.html
week 1897: '-' vs. '+' teqc options - http://postal.unavco.org/pipermail/teqc/2016/002076.html
week 1898: auto-identification of formats - http://postal.unavco.org/pipermail/teqc/2016/002092.html
week 1899: auto-identification vs. format flags - http://postal.unavco.org/pipermail/teqc/2016/002096.html
week 1900: square brackets in options - http://postal.unavco.org/pipermail/teqc/2016/002105.html
week 1901: using option '+mds' - http://postal.unavco.org/pipermail/teqc/2016/002108.html
week 1902: qc results w/ problematic nav messages - http://postal.unavco.org/pipermail/teqc/2016/002113.html
week 1903: '-no_orb[it]' and '-no_pos[ition]' options - http://postal.unavco.org/pipermail/teqc/2016/002115.html
week 1904: '-week' option - http://postal.unavco.org/pipermail/teqc/2016/002117.html
week 1905: using '+bcf' for XYZ/geodetic conversion - http://postal.unavco.org/pipermail/teqc/2016/002126.html
week 1906: the '+v[erify]' option - http://postal.unavco.org/pipermail/teqc/2016/002128.html
week 1907: '+C2', '+L5', "+L6', '+L7', '+L8', '+all' options - http://postal.unavco.org/pipermail/teqc/2016/002130.html
week 1908: getting RINEX doppler and L2 - http://postal.unavco.org/pipermail/teqc/2016/002131.html
week 1909: using paths w/ file names - http://postal.unavco.org/pipermail/teqc/2016/002132.html
week 1910: the (un)importance of file names - http://postal.unavco.org/pipermail/teqc/2016/002133.html
week 1911: notices, warnings, and errors - http://postal.unavco.org/pipermail/teqc/2016/002134.html
week 1912: the '-max_rx_SVs' option - http://postal.unavco.org/pipermail/teqc/2016/002137.html
week 1913: the end of '++igs' and '+igs' - http://postal.unavco.org/pipermail/teqc/2016/002140.html
week 1914: splicing together RINEX files - http://postal.unavco.org/pipermail/teqc/2016/002144.html
week 1915: using '-O.int' and '-O.dec' - http://postal.unavco.org/pipermail/teqc/2016/002145.html
week 1916: '+doy' option - http://postal.unavco.org/pipermail/teqc/2016/002146.html
week 1917: '-tbin' and '-ast' options - http://postal.unavco.org/pipermail/teqc/2016/002152.html
week 1918: mp12 RMS before/after Oct 2013 - http://postal.unavco.org/pipermail/teqc/2016/002158.html
week 1919: the global windowing options - http://postal.unavco.org/pipermail/teqc/2016/002159.html
week 1920: '-M.dec' and '-N.dec' options - http://postal.unavco.org/pipermail/teqc/2016/002163.html
week 1921: combining time filtering options - http://postal.unavco.org/pipermail/teqc/2016/002176.html
week 1922: helping me (or someone else on the list) help you - http://postal.unavco.org/pipermail/teqc/2016/002187.html
week 1923: the "build" line - http://postal.unavco.org/pipermail/teqc/2016/002190.html
week 1924: the qc '-w[idth]' option - http://postal.unavco.org/pipermail/teqc/2016/002193.html
week 1925: qc with explicit time windowing - http://postal.unavco.org/pipermail/teqc/2016/002194.html
week 1926: the '+rx_state' option - http://postal.unavco.org/pipermail/teqc/2016/002200.html
week 1927: the '-O.sum' option - http://postal.unavco.org/pipermail/teqc/2016/002204.html
week 1928: the '+meta' and '+mds' options - http://postal.unavco.org/pipermail/teqc/2016/002206.html
week 1930: more on '-O.sum' - http://postal.unavco.org/pipermail/teqc/2017/002207.html
week 1931: the '-O.s[ystem]' option - http://postal.unavco.org/pipermail/teqc/2017/002208.html
week 1932: leap seconds - http://postal.unavco.org/pipermail/teqc/2017/002215.html
week 1936: what you can (and shouldn't) do in a RINEX obs file - http://postal.unavco.org/pipermail/teqc/2017/002229.html
week 1938: the '+psp' option - http://postal.unavco.org/pipermail/teqc/2017/002231.html
week 1939: the '+diag' option - http://postal.unavco.org/pipermail/teqc/2017/002235.html
week 1951: '-n_<system>' and SV filtering options - http://postal.unavco.org/pipermail/teqc/2017/002277.html
week 1953: more with '+diag' option - http://postal.unavco.org/pipermail/teqc/2017/002287.html
week 1954: using '+diag' output to split raw files - http://postal.unavco.org/pipermail/teqc/2017/002290.html
week 1955: current qc notation - http://postal.unavco.org/pipermail/teqc/2017/002302.html
week 1956: the '+qcq' option - http://postal.unavco.org/pipermail/teqc/2017/002304.html
week 1957: using Trimble formats - http://postal.unavco.org/pipermail/teqc/2017/002305.html
week 1958: ToC != ToE messages - http://postal.unavco.org/pipermail/teqc/2017/002310.html
week 1959: receivers vs. formats - http://postal.unavco.org/pipermail/teqc/2017/002311.html

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