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Rinex.obs "TIME OF FIRST OBS" 1980
336 4 2020-8-27
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Geomaticist
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I have noticed that once in awhile the Phantom 4 RTK will mess up the TIME OF FIRST OBS in the rinex file it writes to the sd card. For some reason it will use 1980 as the year and also the wrong month, and sometimes wrong day. But the time will be right.

I have been able to manually edit the year, month, day in both spots (rinex header and the first time stamp in the data) and then have been able ot successfully PPK the data. Wondering if anyone else is seeing this happen? We use TOPOSETTER to process the ppk, which is really just a clever wrapper over rtklib (but it handles some needed stuff in addition to rtklib.)

Anyhow, wanted to mention this. I cannot really find much on google about it. One person mentioned it as an issue.

I am unsure what is causing it. An example recently was a area we mapped that resulted in 4 folders of pics, and each has the usual rinex and mark files. The first folder has 1980, and the next two folders have the correct dates (2020), then the last one again has the wrong date (1980). Again this is only the TIME OF FIRST OBS entry. the rest of the rinex is all 2020.


2020-8-27
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patiam
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"For some reason it will use 1980 as the year and also the wrong month, and sometimes wrong day"

GPS time is a count of the number of weeks, and seconds of the current week, since an epoch. The start epoch was 0 hours (midnight) Sunday 6-Jan-1980, when GPS time was 0.

When a GPS  time message is corrupted, truncated, or wrongly interpreted, it leads to incorrect timestamps. This can happen for a lot of reasons.

As for how to prevent it from happening with the P4RTK, I don't have any magic bullets. It may be that you can suss it out by looking for patterns in the manner in which the TOFO stamp is wrong.

Due to CoVid, I don't have access to our P4RTK to test myself. This may change in the coming weeks or months. That being said, I haven't used PPK on our P4RTK, only RTK w/ NTRIP.

I know this probably doesn't help much, but at least now you know why you keep going back to 1980.
2020-8-28
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Geomaticist
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patiam Posted at 8-28 13:13
"For some reason it will use 1980 as the year and also the wrong month, and sometimes wrong day"

GPS time is a count of the number of weeks, and seconds of the current week, since an epoch. The start epoch was 0 hours (midnight) Sunday 6-Jan-1980, when GPS time was 0.

thank you. Yeah very helpful. I bet it is glitching out on the TIME OF FIRST OBS. I will keep track and see if I find a pattern.  We were doing RTK a lot. I am a Surveyor. We use Trimble R10 and have it cast out NTRIP through its wifi and then connect the P4RTK to it. Works good. Sometimes drops and we seem to have sorted the issue a little. but since we are always doing complex surveys and cannot always have known coordinates it means that RTK can be draft at best. So it has been very helpful to have a PPK option. So we can use some final coordinate and then update the image positions to that - before running the data into a photo processing app.

For the record - I use Trimble R10, P4RTK, TOPOSETTER 2.0, and Agisoft METASHAPE. Then use Global Mapper and put final products into our own custom designed low distortion projections. Quite a bit to know but it is worth it.

in case anyone else searches and finds this topic - I have had success with simply editing the rinex files to fix the 1980 glitch. And I don't think this has affected live RTK, it might have … but no proof. I suspect RTK wont fix until it starts getting correct GNSS data and times. So it will take a whopping 1 second longer … the next epoch. But this issue does affect the ability to PPK.

As a side note the PPK seems to get exactly the same final product precision as the RTK, or better. So far never worse.
2020-8-28
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Break051
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Have any of you had the issue where the P4 RTK will store images in the media folder rather than the Survey folder?  This makes it impossible to Post process images due to there being no Rinex or OBS files for these images.  I can never tell if its storing it in the right folder until after the flight is complete.
2020-9-18
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patiam
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Break051 Posted at 9-18 03:56
Have any of you had the issue where the P4 RTK will store images in the media folder rather than the Survey folder?  This makes it impossible to Post process images due to there being no Rinex or OBS files for these images.  I can never tell if its storing it in the right folder until after the flight is complete.

never had that happen myself. you're using the GS RTK app exactly the same way when this occurs, but somehow the storage locations change unexpectedly? weird.

does it help maybe to completely wipe the card before flying?
2020-9-18
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