RTKPOST error: no nav data

[Hugo Bertiche Argila]

So, I'd like to postprocess the data recorded with Piksi, using RTKLIB.

The outputs of Piksi's Console are these files: rover[...].obs, rover[...].eph, base[...].obs, base[...].eph

Using these files as inputs in RTKPOST.exe returns an error, "error: no nav data".

Is this an extra file I need? If so, why isn't an output of Piksi? How do I obtain this data?

Also, I'd like to be able to automatically record rover's observations in a SD card or something similar, without using a laptop or anything else, to avoid relying on telemetry.

One more thing, I'm really new in this stuff, so I'd really appreciate an "RTK for dummies" answer :P

Thanks in advance for your help.

[Mehdi Daakir]

Hi,

When RTKlib complains about "no nav data" it means that you don't give the right nav file as input.
Check your .eph file and that you put it in the right field for RTKlib.

Regards,

[Clive Turvey]

>>Also, I'd like to be able to automatically record rover's observations in a SD card or something similar, without using a laptop or anything else, to avoid relying on telemetry.

Well I think you're going to need something else because the Piksi doesn't have an SD Card socket. You'd want to look for something that can log serial data, or build a small micro (STM32 + MicroSD) to record the data.

The Navigation data (*.??n) file can be pulled from a number of sources, it's the broadcast ephemeris, so any receiver with a similar sky view will work, and the CORS ftp site has an amalgamation of ephemeris received across all sites. Countries outside the US may also have their own resources.

Precise ephemeris (*.sp3) can also be downloaded, these are actual measurements rather than curve fit projections transmitted by the satellites.

[Hugo Bertiche Argila]

Here are the files given by Piksi. Is it possible to use them with RTKLIB as they are? Or do I have to do something before (conversion or something)? Or maybe the files are incomplete or corrupted? How could I know?

Also, RTKPOST.exe has 2 fields for rover and base observations (.obs) and 3 extra fields. In which of them should I introduce my .eph files?

Thanks for your time

[Hugo Bertiche Argila]

I've found a website that provides nav data. Using this file there is no 'no nav data' error, but the output file is empty, just the header.

Why?? T_T

[Hugo Bertiche Argila]

Also, for the data logging, which baud rate should I use?

[Clive Turvey]

The USB VCP is 1Mbit as I recall, and the radio's UART A 115200 8N1, but you should be able to configure them via the console/settings, along with the data type and mask settings.

[Felipe G. Nievinski]

On Monday, April 27, 2015 at 7:09:19 AM UTC-3, Hugo Bertiche Argila wrote:

Here are the files given by Piksi. Is it possible to use them with RTKLIB as they are? Or do I have to do something before (conversion or something)? Or maybe the files are incomplete or corrupted? How could I know?

Also, RTKPOST.exe has 2 fields for rover and base observations (.obs) and 3 extra fields. In which of them should I introduce my .eph files?

AFAIK RTKLIB doesn't support Piksi's EPH format.

-F. 

[Felipe G. Nievinski]

On Monday, April 27, 2015 at 8:20:55 AM UTC-3, Hugo Bertiche Argila wrote:

I've found a website that provides nav data. Using this file there is no 'no nav data' error, but the output file is empty, just the header.

Why?? T_T

I'd have to turn on debugging output in RTKLIB/RTKPOST to know why.

-F. 

[Hugo Bertiche Argila]

Then, how can I postprocess the data? Converting these .eph files? Using another postprocessing software?

[Clive Turvey]

In all honesty I almost never use Navigation (Broadcast Ephemeris) files from the receiver for post-processing, it's always significantly easier to manage them by just pulling the *.??n and *.sp3 files from the internet which can give hourly/daily coverage of the entire constellation. Technically, I don't think the receiver even needs the almanac or ephemeris data to make valid raw measurements.

If the output from the Piksi is unsuitable you have a couple of options, a) you can convert it into a valid RINEX format, b) download it from another source, c) use another receiver in close proximity and with similar sky view to generate the same data. Remember the data is broadcast by the satellite, everyone is going to get the same data from the same satellite, provided they can see it.

-Clive

[Fergus Noble]

Hi Hugo,

Unfortunately there is no supported way to do post processing with Piksi at the current time. That said, I believe there have been several members of the community who have had some success with pose processing with RTKLIB but it did require some experimentation and possibly some modifications/processing of the raw observation output values to make them compatible with RTKLIB.

Using an ephemeris downloaded from the internet as suggested below is definitely the way to go as there is no converter from our ephemeris format to RINEX nav yet.

Also there are some differences in the way we output observations related to the way the receiver clock is handled, possibly a sign difference and some issues around the SNR units as I understand it.

Michael Oborne has written some code that may be helpful here:

https://github.com/meee1/piksi

Here is the corresponding thread:

https://groups.google.com/forum/#!searchin/swiftnav-discuss/rtklib/swiftnav-discuss/KinyH-JpsPk/WoFN2vNl3IAJ 

Sorry I can’t be more helpful. I haven’t tried using Piksi with RTKLIB myself.

Fergus

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CTO & Co-founder

Swift Navigation Inc.
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[Hugo Bertiche Argila]

I tried downloading nav files from http://www.ign.es/ign/layoutIn/geodesiaDatosGNSS.do but when I try to post process, the output file is empty (only headers), I'd like to have a valid nav file so I can check how it must be and maybe even make a script to convert files. If anyone could upload it, it'd be very helpful.
Thanks for your answers.

[Tom]

Use RTKGET to download the navigation (.nav) file for the specified time (in GPS time) using the IGS_NAV ftp that is already loaded in. Load this file into the box under where you input your base station file in RTKPOST. 

I haven't had any luck using SP3 files with the piksi but .nav files seem to work.

[Hugo Bertiche Argila]

I tried to use the RTKGET but it doesn't work. I went to the link where it downloads the data (ftp://cddis.gsfc.nasa.gov/gps/data/daily/2015/141/15n/) but the folders are all empty.

[Stanislaw Nanek]

3 mistake:

1)Intv set to 24H (for nav file) not 15min

2)  you set Local Directory but not set the path eg. C:\  click ikon [...]

3) end time is set before start ( switch )  set start time 00:12 end time 10:05

click download and you have brdc1140.15n 

[Clive Turvey]

We haven't got to day 141 yet?

ftp://www.ngs.noaa.gov/cors/rinex/2015/119/brdc1190.15n.gz

This is a combined file covering all the reference stations, not sure if that has global scope.

[Hugo Bertiche Argila]

Thank you very much, it finally worked!!

There's one more thing I'd like to know, I have connected a datalogger (UART B), and it records the gps coordinates among other things, what I'd like to have is the observations (.obs), that way I wouldn't need to use telemetry. Is there a way to configure UARTB settings to record this? Or a way to reconstruct the data to get a .obs file?

[Stanislaw Nanek]

regarding SNR unit I used https://github.com/swift-nav/piksi_firmware/pull/385 to piksi_firmware and build firmware and update, 

the effect was such that, SNR rose +31 (under "Tracking" in the "pixie console" "dB-Hz" found signals were tracked over those that scan for)

 [note graph here was more transparent if possible it would be excluded from the these PRN chart which "pixie" actually does not track]

then I use Michael Oborne program from https://github.com/meee1/piksi to conversion from SBP to RTCM and use in RTKLIB

S1 value of observation in RTKLIB increased but the problem remained, solutions RTKLIB as if they jump quickly from single (spp) to float and fixed Get around

the problem is probably in the fact that the acquisition to specific PRN is not continuous

eg. in RTKLIB disappears signal to a satellite which has the highest C / N0 in the "pixie console"

and so, eg. in the "pixie console" I have a constant amount of satellites np.7 and RTKLIB after conversion (SBP> RTCM) the number of satellites jumps between 3 and 6.

(view in attach RTKLIB-Nsat-plot.jpg) and fixed solutions are jumping about 50m (view in attach RTKLIB-Position-plot.jpg and RTKLIB-GndTrk-plot.jpg)

Color in plot:

Red= singiel(spp) solution

Orange= float solution

Green= Fixed solution

P.S. I think it would be best to implement the format "sbp" in RTKLIB

[Clive Turvey]

You'd need to set a suitable mask, like that for UARTA, which is outputting the Rover's observations in the SBP format. These are the observations you see at the base console over the radio, you can record either the Base or Rover observations to RINEX at the console.

The code Fergus pointed too earlier should get from SBP to RINEX if I read the summary correctly, you could store that stream directly and decode it later, or build something to parse the SBP directly into RINEX files.

[WQFlowers WQFlowers]

Hi. I would like to know, how can i get "RTK" and who can help me in installation?

суббота, 25 апреля 2015 г., 16:01:54 UTC+5 пользователь Hugo Bertiche Argila написал:

[Stanislaw Nanek]

for now I have to test in the field, because this test was in very poor conditions, the antenna close to the wall of a tall building, half the sky obscured.

and on the "pixie STM Firmware Version: v0.15.1-85-gee3dfff" observations S1, in RTKLIB no longer jump to 0

[Antonio Carannante]

Hi everyone, I would like to download from RTKPLOT, the DOP to a text file , but I see this message "No Nav Data" ,  how can I solve this problem?

This is what I see