[FOSS-GPS] RTKLib fixed baseline length

David Kelley DavidKelley at iTSware.net
Sat Apr 2 18:23:39 PDT 2016

Well, hummm..
Post the two files if you can for others to tinker with.  Recall that 
RTCM 1004 will not carry the Doppler that you might have originally had 
(so it may not be present in your RINEX files if that is what was 
converted), so you might be better of post processing with raw data (or 
MSM type RTCM if you get it).  Doppler is very useful here, esp with L1 
only.  I have not used the baseline constraint in RTKLIB, so can not 
comment on its use or value here, would have to dig into the actual 
code.  In any event, with the moving baseline method expect to see 
noticeable loses the positional estimate reported, in favor of a better 
estimate or the yaw and pitch. [you can see that with the two reference 
stations I pointed you to, in static you will see <5mm variation]  This 
method is at its best for a ship or plane.  If your antenna are set are 
too close  ( say~<50 cm), or they interfere with each other (due to the 
down convert local oscillator crosstalk between identical GNSS devices), 
other issues will of course arise.   Just some quick guesses.
Good luck, regards DCKelley

On 4/2/2016 5:02 PM, Marco Mendonça wrote:
> Thanks, David!
> I'm actually trying to post process two RINEX files on rtkpost from 
> antennas on a car. I chose the moving baseline option, set the 
> baseline length, but still, no solution.
> When not setting the baseline length as fixed, it works fine. Although 
> the estimated baseline is close to the real value, I'd like it to be 
> fixed.
> I'm also using moving baseline. With the length constraint, the 
> results are noisy and only with 1.07% fixed epochs. Without the 
> constraint, the fixed epochs are around 90% and much smoother and 
> coherent. And I'm absolutely sure about the distance from antenna to 
> antenna.
> Also, thanks for the example provided! I'll connect there and try to 
> debug my option choices. Any other guesses of what might be happening 
> are greatly appreciated!
> Regards,
> Marco
>     Date: Sat, 2 Apr 2016 15:09:23 -0700
>     From: David Kelley <DavidKelley at iTSware.net>
>     To: Open Source GPS-related discussion and support
>             <foss-gps at lists.osgeo.org
>     <mailto:foss-gps at lists.osgeo.org>>, mammendonca at gmail.com
>     <mailto:mammendonca at gmail.com>Subject: Re: [FOSS-GPS] RTKLib fixed
>     baseline length
>     Message-ID: <57004313.4050509 at iTSware.net>
>     Content-Type: text/plain; charset="utf-8"; Format="flowed"
>     Marco :
>     Works fine for me as well.
>     There are no "special" switches, does it first work for you when
>     stationary? Start with getting that to work as a first step.
>     If you have it working in the mode "Kinematic" (ie normal moving rover
>     RTK) or "Static" (ie stationary RTK where measurement noise is
>     taken out
>     in dithering the clock estimate more than the position), then
>     "Moving-Base" should work as well.   I presume you know the reason for
>     using this mode is often to get a precise estimate of the rovers
>     heading.
>     Here is an image of it working in that mode on short 130cm baseline.
>     You can see that the two antenna are nearly, not not 100% located N-S
>     with respect to each other.  The ~0.1 degree shift is because the West
>     side of office building does not run a true north-south!   Feel
>     free to
>     connect to the SNIP NTRIP casters that are listed on the image
>     below to
>     confirm everything else is working.  [No user id is needed, and
>     Serv2.itsware.net:2101 <http://serv2.itsware.net:2101/> is left up
>     during the weekend. Not guarantees
>     during the US work week as that is used a testing machine.]
>     Good luck!
>     Regards,  DC Kelley
> - Marco Mendonça
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David Kelley
ITS Programs Manager, SubCarrier Systems Corp. (SCSC)
626-485-7528 (Cell) 626-513-7715 (Office) 888-950-8747 (Main)
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