GPSMAP 67 RINEX data

Discussion related to the Garmin GPSMAP 67 series GPSr
JungleJim
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Re: GPSMAP 67 RINEX data

Unread post by JungleJim »

Thanks that’s great. I also had contact with US support via chat, and they created a ticket and asked to send details. So hopefully Garmin will resolve these issues.
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mimichris
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Re: GPSMAP 67 RINEX data

Unread post by mimichris »

JungleJim wrote: Thu Apr 13, 2023 4:20 pm In its current form, the RINEX data for Galileo and BDS does not conform to specification and there is no L5/B2a data in the file, data that the device for sure has available (because shown on the satellite page).

You can easily see this if you open the 67 and 66sr RINEX files in a text editor, as they are simple text files.

So somewhere on the device the conversion of available GNSS data into RINEX format goes wrong.

It may be that the 67 does some “tricks” to conserve battery life, but you cannot draw this conclusion on the current RINEX data since it is invalid and incomplete :)

It would be very interesting to compare valid 67 RINEX data to what is shown on the satellite page, but at the moment this is simply not possible.
In this extract from Rinex, we see the GPS and Glonass, but below there is E and C are they Galileo and Beidou ?

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*** Image formatting corrected to comply with forum guidelines ***
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Presse-papiers-1.jpg
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GPSMAP66sr, GPSMAP67, GPSII+, Twonav Cross.
JungleJim
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Re: GPSMAP 67 RINEX data

Unread post by JungleJim »

Yes, the E and the C indicate Galileo and BeiDou systems. So G=GPS, R=Glonass, E=Galileo, C=BeiDou, J=QZSS, I=IRNSS (NavIC).

In your screenshot you also see the issues with the current RINEX data:
  • Galileo and BeiDou satellite numbers have an incorrect format. It should be Enn and Cnn, just like GPS and Glonass.
  • there are duplicate records, for example satellites G12 is listed two times (although with same data). This occurs for many satellites.
  • only data from a single band is present (the 4 numbers after the satellite number). Compare this with the following screenshot from the 66sr data, where you see up to 8 data points (L1 + L5) for GPS and Galileo:
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    66sr multi-band data.png
The RINEX data is based on fixed length records, so if there are blanks there is no data. For example see G23 in your screenshot, it only has the fourth data point (which in this case is Signal Strength), the first three are unavailable (Pseudo Range, Carrier Phase and Doppler shift).

If you're interested, the specification of RINEX 3.04 is available here:
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mimichris
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Re: GPSMAP 67 RINEX data

Unread post by mimichris »

Thank you for this information but as it is in English and my English is very weak.... What would be interesting is to have software that translates the RINEX, I searched on the Internet but I did not have not found except those I have...

I looked at a 66sr Rinex with another text reader, indeed it is like your example, we see L1 and L5 as well as Galileo E1 and Ea5, but not that of the 67 which does not have the same presentation at all, Garmin changed something?
GPSMAP66sr, GPSMAP67, GPSII+, Twonav Cross.
JungleJim
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Re: GPSMAP 67 RINEX data

Unread post by JungleJim »

The image is just a screenshot of the text editor I use. I added the red rectangles and L1/L5 text to the screenshot myself to clarify. The data is from the 66sr file you posted earlier in this thread.

And indeed there is not a lot of software freely available for processing RINEX files. RTKLIB is one of the more well known. I also found GFZRNX. And there are a couple of commercial software providers.
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Gadwin
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Re: GPSMAP 67 RINEX data

Unread post by Gadwin »

I don't know how severe the dpulicates bars are at the satellite page, but I have the hunch, that this is just a visual bug of the multi-bands. Normally in 66sr every galileo satellite had E1 and E5a, but now in 67 those satellites which have a duplicated E1 bars don't have the E5a bar anymore, so I guess the duplicated bars in E1 are in fact one bar for E1 and the other for E5a. Especially if you look at the screenshots under Bug 2 of 67, you will see that the duplicated bars are not real clones of each others, because they display different signal quality.

That is probably the same in the RINEX file.
JungleJim
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Re: GPSMAP 67 RINEX data

Unread post by JungleJim »

Gadwin wrote: Fri Apr 14, 2023 9:38 am I don't know how severe the dpulicates bars are at the satellite page, but I have the hunch, that this is just a visual bug of the multi-bands. Normally in 66sr every galileo satellite had E1 and E5a, but now in 67 those satellites which have a duplicated E1 bars don't have the E5a bar anymore, so I guess the duplicated bars in E1 are in fact one bar for E1 and the other for E5a. Especially if you look at the screenshots under Bug 2 of 67, you will see that the duplicated bars are not real clones of each others, because they display different signal quality.

That is probably the same in the RINEX file.
Yes my guess is also that the duplicate bars in the satellite page is just a visual bug because as you say the duplicate bars have different height (ie. value).

But in the RINEX file this is not the case because the duplicate records are full duplicates. In other words all values are completely the same. And also the correct format would be that all values (for a single satellite) would be on a single line and not on two.
Duplicate observation records in RINEX data
67 RINEX duplicate records.png
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mimichris
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Re: GPSMAP 67 RINEX data

Unread post by mimichris »

From what I understand Garmin has modified the Rinex or it is misinterpreted by the 67 and why? While that of the 66sr is perfect and without duplicates.

This does not prevent us from seeing that the 67's GPS works intermittently because on the RTKPLOT graph we only see points (from GPS and Glonass) which correspond to the geographical position of the recorded points and not a continuous line like the 66sr, which from my point of view justifies the power saving function.
Apart from the low-consumption components, you also have to find a solution to save the battery and find the 144 hours of autonomy compared to the 30 hours of the 66sr.
GPSMAP66sr, GPSMAP67, GPSII+, Twonav Cross.
JungleJim
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Re: GPSMAP 67 RINEX data

Unread post by JungleJim »

mimichris wrote: Fri Apr 14, 2023 10:53 am From what I understand Garmin has modified the Rinex or it is misinterpreted by the 67 and why? While that of the 66sr is perfect and without duplicates.
There is obviously a bug in creating the RINEX data. Why? Only Garmin knows.
mimichris wrote: Fri Apr 14, 2023 10:53 am This does not prevent us from seeing that the 67's GPS works intermittently because on the RTKPLOT graph we only see points (from GPS and Glonass) which correspond to the geographical position of the recorded points and not a continuous line like the 66sr, which from my point of view justifies the power saving function.
Compare it with looking at a picture that has parts missing and other parts are distorted (wrong). You can guess what it is but chances are you will be wrong... So unless we have correct and complete RINEX data we simply do not know for sure!
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JungleJim
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Re: GPSMAP 67 RINEX data

Unread post by JungleJim »

Unfortunately with device software 5.30 no fixes for the RINEX issues reported here :cry:
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