[teqc] helpful tip of week 1903
lou at unavco.org
Wed Jun 29 07:39:40 MDT 2016
This week's tip: the '-no_orb[it]' and '-no_pos[ition]' options
These options were added back in April-August 2011 and finalized (in their current
form) on 1 Aug 2011. I wanted to bring these up in last week's helpful tip
on how to help check whether a strange qc result was due to problematic navigation
messages -- rather than problematic observation data -- but that tip's writeup was
getting rather long. So recall from last week:
If you are doing a full qc -- using navigation messages for orbit computation --
weird problems might not be due to the observation data. The problems might
very well be with the navigation messages you are using:
- Try a qc "lite" (without navigation messages). Does the qc "lite" look good?
- Look for unhealthy SVs; if any are found, try filtering them out.
- Try using the combined broadcast RINEX nav files from CDDIS or another center
(and filter out unhealthy SVs).
The options '-no_orb[it]' and '-no_pos[ition]' allow you to do a qc lite or
a partial qc full using only a subset of constellations very quickly. These two
options are almost identical:
 teqc +help | grep no_
-no_orb[it] <list> don't use orbits for listed constellations (G,R,S,E,C,J) in qc, e.g. <list> = R+E
-no_pos[ition] <list> don't use orbits for listed constellations (G,R,S,E,C,J) in qc's ppp, e.g. <list> = R+E
Ok, what's the difference? Specifying a constellation with '-no_orb[it]' during
a quality check (qc) means that no orbit calculations whatsoever are done with
that constellation; that constellation will be done in a qc 'lite' mode even
if navigation messages for that constellation are present. Therefore, elevation
and azimuth calculations are not done for that constellation (e.g. no entries in
the .ele and .azi compact3 files if '+plot' is used).
The '-no_pos[ition]' option does the orbit calculation for the specified constellation
(if navigation messages for that constellation are present), so elevation and azimuth
calculations _are_ done for that constellation. But now that constellation is not used
in teqc position solution for the antenna.
Deciding which to use depends on what you want or don't want.
As you probably know, when qcing RINEX observation files, teqc automatically looks
for name-matching RINEX navigation files in the same directory/folder, using the
same filename prefix as the observation file) and reads any nav files found.
The same thing happens when using either '-no_orb[it]' or '-no_pos[ition]', so the
reading/formatting validity of any such RINEX nav files continues to be checked.
Before these options were introduced, the only way to make teqc ignore a RINEX nav
file during qc (assuming it was named with the same filename prefix as the RINEX
observation file) was to move the RINEX nav file to a different directory/folder
or to rename it in some non-canonical way. However, if the RINEX nav file being
eliminated in either of these two ways was for GLONASS, then teqc was probably not
going to be able to do a qc 'lite' analysis. Why? One needs to be able to convert
phase data, in units of phase cycles in RINEX, to units of distance and this conversion
for GLONASS FDMA signals requires the GLONASS slot to frequency channel number (fcn)
for each GLONASS SV with phase and pseudorange data. This slot-to-fcn mapping can
be provided without a GLONASS RINEX nav file (i.e. see the '-glonass_s2fcn' option),
but normal teqc use extracts this mapping from the GLONASS RINEX nav file(s).
Upshot: Using '-no_pos R' or '-no_orb R' allows you to shut off use of GLONASS
orbits (to help see if the GLONASS navigation information is suspect or not),
but still lets teqc read any GLONASS navigation information to obtain the slot
to fcn mapping so that a qc "lite" can be applied to the GLONASS data. (But:
problems in the qc with GLONASS data might still arise, however, if the fcn happens
to be wrong in the navigation messages for one or more GLONASS SVs.)
Can the '-no_orb[it]' and '-no_pos[ition]' options be used together in one command
with different constellations? Yes (... or at least this should work aok). For
example, using '+qc -no_orb R -no_pos E' should completely skip doing the orbit
calculations for GLONASS (and therefore no elevation and azimuth values for GLONASS
SVs in the .ele and .azi files if '+plot' is also included), whereas Galileo SVs
should have orbit calculations done, but Galileo data should not be used in teqc's
antenna position calculation in this run. And both GLONASS and Galileo SVs should
have a qc 'lite' done.
A couple last notes: Multiple constellations can be specified with the '-no_pos[ition]'
and '-no_orb[it]' options, as shown in the `teqc +help` usage. You can include
a delimiter character, like '+', or ',': '-no_pos R+E' or '-no_pos R,E' ...
or just leave out delimiter characters: '-no_pos RE'. So to switch to a
qc 'lite' on all constellations, whether data for them are present or not,
you could use, say, '-no_pos G,R,S,E,C,J' or '-no_orb G,R,S,E,C,J"
p.s. This is the 10th "tip of the week". Are these really helpful ... or
am I just boring most of you all to a near comatose state?
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
WWW: http://www.unavco.org http://jules.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
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