[teqc] Teqc questions

[Richard Langley]

There are a number of on-line precise-point-positioning services to which you
can submit a RINEX file for processing. You should try one of those as another
check on the quality of your data.
-- Richard Langley

On Thu, 23 Mar 2006, Lou Estey wrote:

>Dear Stav,
>
>> Hi I am a phd from toulouse and I would like to ask u about the teqc +qc
>> +eepx option,
>> there is a couple of days since we've received a warning call from EUREF
>> about our station here in Toulouse TLSE concerning a low observation
>> quantity problem since doy 228 - 240 2005. So, as already being very
>> curious about knowing what's going on i've started doing comparative
>> analyses of MP1 MP2 SNR1 SNR2 for a period of 2-3 months from doy 213 -
>> 300 2005. Though as I do like "playing" with softwares I used ur option
>> teqc +qc +eepx -nav brdc2480.05n tlse2480.05o for several doys. So what
>> I get is something like the picture further down. So my question I guess
>> is : why do we have such a bad quality in navigation position and
>> specially after the midle of the day? Isn't a navigation position
>> supossed to be erroneous of about 10m to 20m? Because here we can
>> clearly see that after the middle of the day we get something like a
>> hundreds of meters of variation. Of course the last question would be, I
>> 'am doing something wrong with the option +eepx?
>
>My guess is that you are using +eepx correctly, and yes, currently
>(with SA = selective availability turned off) one could get a position
>with an rms of 10-20m -- maybe even down to 3-5m at times, assuming
>all possible corrections are made.  But teqc doesn't do all possible
>position corrections, and is even pretty sloppy in parts (using a
>arithmetic average of the L1- and L2-code pseudoranges, assuming the
>paths are entirely in a vacuum, not accounting for the rotation of
>the Earth during the signal transmission, etc.).  Grossly speaking
>I'd say the teqc position is only good to ~100m horizontally and
>somewhat larger than that vertically -- about what a handheld receiver
>was circa mid-'90s when SA was on.  The idea at the time was to give
>an engineer in the field reasonable confidence that the receiver | download/stream
>of the data | data translation to RINEX pipeline was giving them something
>reasonable and they weren't wasting their time collecting garbage.
>This is still the main idea of what `teqc +qc` is supposed to do.
>
>As to why the `teqc +qc +eepx` position degrades towards the middle of
>the day, especially for days 248/249 which is during the period that
>EUREF says this site has a low observation quantity -- although there is
>also a lesser degradation of the position in the data for days 100/101:
>We suspect there is a long-standing bug in teqc.  This behaviour was
>seen by Jim Johnson over five or six years ago (-- somewhere I still have
>the paperwork on his experiment! --), but the cause in the code was
>never tracked down.  From your data it appears that the bad position
>is exacerbated by poor tracking, i.e. lower observation quantity.
>But even the worst part of your +eepx results show an rms that is
>on the order of 100m -- which is about what I'd expect from teqc anyway.
>
>Hope this helps,
>--lou
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>teqc at ls.unavco.org
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>


===============================================================================
 Richard B. Langley                            E-mail: lang at unb.ca
 Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/
 Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142
 University of New Brunswick                   Fax:      +1 506 453-4943
 Fredericton, N.B., Canada  E3B 5A3
     Fredericton?  Where's that?  See: http://www.city.fredericton.nb.ca/
===============================================================================