Re: FOSS-GPS Digest, Vol 102, Issue 2

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Re: FOSS-GPS Digest, Vol 102, Issue 2

dskumher
which messages from the base raw binary data are redundant & not needed by rover strictly  & hence need not be sent,
in other words which messages are  necessarily required from the base raw binary data for quality RTK fix when the internet
speed is slow for transferring data through NTRIP ? How to do it in SNIP while sending serial stream in raw binary data form from base ?

Regards,
Dhirendra singh,
INDIA

On Thu, Aug 24, 2017 at 12:30 AM, <[hidden email]> wrote:
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Today's Topics:

   1. Re: Post Processing with RTKLIB ([hidden email])
   2. Re: Post Processing with RTKLIB (RTKPostProcess)
   3. Re: Post Processing with RTKLIB ([hidden email])


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Message: 1
Date: Tue, 22 Aug 2017 13:35:42 -0700 (MST)
From: "[hidden email]" <[hidden email]>
To: [hidden email]
Subject: Re: [FOSS-GPS] Post Processing with RTKLIB
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=us-ascii

Post processing raw observation data gathered in the field has been very
common decades and you should have no problems using RTKLIB (the RTKPOST
tool) for that.  Many "old timers" still do it that way for various reasons
and when we are in the filed we are checking as we go but we old "trust" the
post processed results.  And post processioning means you can also use final
orbits and other data products that are readily available to get better
results.  All of this is moot if your field data is itself corrupted.  And
you can easily turn RTCM3.x into RINEX files with other RTKLIB tools and
find 3rd party processing services to solve it for you.

Time synchronization will not in fact be an issue.  RTCM 3.x provides the
precise time over the current GPS week, so you have to tell the tool (RTKLIB
or any other such tool) what week a file came from but the file name
conventions used often help with that.  There are a few other messages and
tricks, but this solves 99% of your issues.  The navigation filter will then
determine the precise time.

The data from the "nearest RTK" station of course depends on where you are.
Many tools (RTKLIB, SNIP, and often the NTRIP Caster device itself) will
provide a means to capture the raw RTCM data for your post processing needs.
NGS CORS even runs a long term FTP site with such data, but the data is
decimated.  Depending on your application that may not be an issue.

*So yes this is quite possible and routinely done*. But you have not told
the group anything more about the devices in the field (the rovers) and what
span of location and how often the positional estimates are wanted, what
precision is required, etc. Many of the practical details and useful advice
you might get will turn on that.    Regards, DCK



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Message: 2
Date: Tue, 22 Aug 2017 23:42:35 -0700 (MST)
From: RTKPostProcess <[hidden email]>
To: [hidden email]
Subject: Re: [FOSS-GPS] Post Processing with RTKLIB
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=us-ascii

Thank you for your answer,
The device contains an NV08C-CSM GNSS module, with 2JM013-010/113-UFL
antenna. The desired precision is 2cm, and we need them as often as
possible, we want a really precise route from the FIX data.
My problem with the synchronization is that we can capture both the rover
and the base station data, but because we capture it in two different place,
it maybe cause some problem when we want to process it. For example because
of the slow internet connection or anything else the .tag file we create for
this probably will have a few second delay.

Best regards,
Greg



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------------------------------

Message: 3
Date: Wed, 23 Aug 2017 03:19:02 -0700 (MST)
From: "[hidden email]" <[hidden email]>
To: [hidden email]
Subject: Re: [FOSS-GPS] Post Processing with RTKLIB
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=us-ascii

In this case you are planning to use low lost L1 only device with a ten
dollar patch antenna.  Search for Michele Bavaro to find practical use tips
on that chip and RTKLIB.  By now you probably know L1/L2 is to be preferred,
and that you need to be <15km (better yet <10km) from your base stations to
get fixes with this setup.  We have done RTK mobile <2cm work on vehicles
with the NV08 and RTKLIB, but we tend to use better antenna (see
https://www.use-snip.com/kb/knowledge-base/question-what-antenna-should-i-use/).
You do not state your data rates, only "as often as possible" - to some
people that means 1Hz, to others much more (that chip does 20hz with the
normal increase in measurement noise floor). One presumes you have a
generally clear sky? No forest cover? Is this a drone, a ground vehicle or a
manpack or other? This directly effects the expectations of signal loss you
will have.  You will end up with lots of data, in the NV08 propriety format,
that you will then translate to RTCM3 or to RINEX for use in post. And
RTKLIB does all that just fine.

If you are processing "at the end of the day" then the slow internet should
not matter here (see prior reply about time tags, I do not think you will
need to use the tag option), but perhaps I do not understand your config. It
is likely you will want to record the RTCM streams from all the base
stations your device may be near and select which is best in post.  You have
not mentioned what the span of rover operation would be.  BTW, a point I
failed to note in my first post of that you need not send a precise / good
position to the NTRIP Caster and you only need to send it once.  For most
needs, a 1km will suit, so in fact the unaided fix from this device in
NMEA-183 format will be fine (or you can add it by hand). The Caster will
then pick the best station to send to you (and you will get the exact
location for that data).



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