[gpsd-users] recording and playback of NMEA sentences with millisecond timestamp

[Bernd Büchs]

Dear gpsd-user members,

up to now I record GPS data in NMEA format (5Hz receiver) via gpspipe
and play it back via gpsfake. When playing back I use the "-c" option to
get my expected 5 positions per second.

When analysing the playback timing with an own gpsd client*) I
recognized that the time differences over one second are not equally
distributed as on the real device. It seems that the real device sends
some satellite information only once in the first 200ms "block" and than
just the postions, while the gpsfake player distributes the sentences
equally.

Therefor I would like to add a millisecond timestamp when recording and
ask the gpsfake player to considder this timestamp (differnce between
sentences) during replay.

I came across the gpspipe '-T' and '-t' options, but '-T +%s3N' as
format like in date command does not work. I think  strftime() simply
does not support milliseconds or nanoseconds...

The second part gpsfake seems not to have an option to honor
(millisecond) timestamps either...

How would you do that?
Did I overlook some options?
Are there other tools for that?

Any pointers to further reading is welcome!

Kind regards


Bernd



*)
It's purpose is to manipulate gpsd information, e.g. change timing,
change speed and accuracy information and provide its output to regular
gpsd clients for testing.