Re: Report GPS/sync time difference

[Roger Oberholtzer]

---

From: gpsd-users on behalf of Gary E. Miller
Sent: Tuesday, October 25, 2022 20:13
To: gpsd-users@nongnu.org
Subject: Re: Report GPS/sync time difference

Yo Roger!



>> As they are high-end (OxTS) designed to be used in a moving vehicle,

> One mans "high-end" is anothers trash.  Care to be more specific?

Very high precision vehicle location and orientation. Among other uses, we use it to help us locate LiDAR and high-resolution image data with such high precision that we can take a pixel from an image and use it to colorize a point in the LiDAR data. And have those colorized points be in space within a couple CM of where it is expected to be. Collected at up to 90 km/k and done at a high volume (35000 KM per year) and, for the most part, an automated process.

>> this means you have to drive a bit. This is also because of the IMU
>> and how it is integrated in positions and orientation.

> Which makes no sense.  Time is from the GPS, not the IMU.

Obviously. But when the goal is that ALL data should be consistent (time, location, orientation), crapping out bits just because you can does not help anyone. It's all about one's use case.

>> Oct 18 13:17:32 rstraptor1 chronyd[2772]: System clock wrong by
>> -67.652005 seconds Oct 18 13:16:24 rstraptor1 chronyd[2772]: System
>> clock was stepped by -67.652005 seconds

> So?  Looks normal.

You have missed the point. Measurements were done where this sync did not happen. Assuming that a PC clock these days is rather stable over a couple months (I know...), perhaps knowing how much it should change the clock today gives a hint how much it might have been moved back when it did not happen.

>> There is the time difference I was after.

> Sadly, by the time you know, it is gone.  So not really a useful answer
> to your question.

In fact it was exactly the answer to my question.

>> If it is the most accurate
>> time difference one can get reported is not clear to me.

> Unless you have a more accurate clock available, that is as good as it
> gets.

I meant that I have to trust that chrony is reporting what I think it is reporting.

>> But it
>> serves my purpose.

> Which is?

All described in my first message in this thread.  And summarized occationally in subsequent messages. Including this one.

Thanks for the help. And thanks for the great software!

Roger Oberholtzer

 

RST Systems

 

Office: +46 (0)10-615 6020

Mobile: +46 (0)70-815 1696

roger.oberholtzer@ramboll.se

________________________________________

 

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden
www.rambollrst.se

Classification: Confidential