Re: ✘NTRIP and RTCM

[Greg Troxel]

"Gary E. Miller" <gem@rellim.com> writes:

>> > All from the Oregon ORGN network.  Many thanks to them for allowing
>> > me cess.  
>> 
>> Indeed, it's very nice of the states to allow public access.  MassDOT
>> runs MaCORS which anyone can use.
>
> Still not as easy as many other countries.

Yes, I guess they could run a caster that does not require login.  I had
to register and I have to use credentials with NTRIP.  But zero cost,
zero justification, and I didn't need to talk to anybody.  Compared to
some other states, I call that a win, but I see your point.

>> I am fuzzy but I gather that RTCM2.3 typically is pseudorange
>> corrections, and GPS only.  It may be L1 only.
>
> Yes, in this case, GPS and L1 only.

So you lose 3 of 4 constellations, and you lose the abiltiy to estimate
iono delay from L1/L2.   Interesting that it makes things worse, but I
am not super surprised.

>> Do you have SBAS disabled, so it is really "no corrections".
>
> I do not have SBAS disabled, but that F9P rarely uses it.  SNAS is
> almost exactly RTCM 2.3

So no L2C, no GLONASS even?  I suppose someone(tm) should get the SBAS
stream and decode it.

>> > c) The synthetic corrections are just WOW.  
>> 
>> Indeed, and you can see the resolution of the coordinates which looks
>> like most of 1 cm.  I wonder if this quantization is in the raw logs
>> or if it could be in the analysis chain.
>
> I'm running in normal mode, with none of the "High Precision" messages.
> Moany of the UBX-NAV-PVT data items are in mm.  Worth a test.

I've been using high-precision NMEA, because my real goal is to log data
in Vespucci for mapping/surveying, and I think I'm seeing well sub cm
quantization.

>> What I would find really useful is:
>> 
>>   record fix mode with each point as metadata
>
> I have all the raw data.  Nothing more can, or could, be recorded.  And
> it is all 3D.

Great, so you should be able to associate with each position what kind
of fix it is.

>>   carry that through analysis and color the dots based on
>>   autonomous/differential/RTK-fixed/RTK-float
>
> u-blox is bad at reporting that.

Do you mean there are no messages that say if the solution is from RTK
FLOAT, RTK FIX, just nav satellites, differential etc like you get in
the mode field of the main NMEA message?

>>   be able to use an input position in the analysis instead of the
>>   average.  I bet your tight value in fix is pretty much right.
>
> Lost me.  Explain?

I think the analysis is computing an average over the hour, and then the
CEP is the distance such that half the points are closer to the
average.  But that's not really "error" because you don't know the right
answer.

I am suggesting, more concretely:

  have the analysis program output the computed average in geojson or
  something into a file, maybe optionally

  have an optional argument to read a "correct answer" from a file in
  that same format

  when given a position this way, compute in terms of that position
  being the truth, rather than assuming that the average of *this
  session* is correct.

What you would do is use the output from the MAX which appears to be RTK
FIX, to process the rest.  That would show you biases among them, even
if you aren't still really sure whihc is right.

>> I am curious what antenna  you are using.
>
> The u-blox one, in a window sill.

Do you mean the slightly larger mouse-style magmount one that is about
$60?  I have one and need to try it.

RTK really wants to be outside with good sky view.  I can sort of get
into fix with IMAX inside, but reliably outside.   I am more like 20
miles from a reference station though.

I measured points at a friends with great sky view and the lock in fix
seemed solid.

>> What I don't understand is why you aren't able to get into FIX with a
>> single reference a mile away.
>
> I don't know if I can or can't.  But that is my long term experience, and
> other see simiilar.

I would love to see data with something like the survey or calibrated
from this line.  I am guessing you have the MB.
  https://www.ardusimple.com/simpleant2b/

The stand is also useful.

So it would be really interesting to see data from your receiver/ant
with the antenna fully outside in a repeatable postion.  I have a
particular deck railing nail I place the stand over.

>> My closest reference is much further,
>> and I use "iMAX".
>
> Do you have doc on "iMAX"?

Will try to dig some up.

>> I am curious how many constallations ORGN is providing data for, and
>> if it's MSM4 or somethihng else.
>
> I'll look at that data next week.  I captured everything.  Only last
> week would gpsd even log that data.

Sure, not complaining, this is awesome progress!

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