[Rock-dev] Adding "Simple" timestamped values

[Janosch Machowinski]

On 10.08.2011 11:59, Willy Lambert wrote:
>
> I am interested in details about this. I have often thougth about such 
> solution when receiving information from hardware that are computed 
> later. Because what is often enougth is to have a precise  timestamp 
> of all your measures, computing later is not a problem. What do you do 
> in such a context ?
We have a helper class called TimestampEstimator. It is part of the
drivers/aggregator package.
This class tries to estimate the correct timestamp. To do this we use
the assumption, that the sensor will provide data on a periodic basis.
Given the period, the TimestampEstimator will compensate for jitter
on the transmission (packets arriving +-Xms around the real time),
and compensate for the clock differences (e.g. sensor firing every 29.5ms
not ever 30ms, from point of view of the PC).

If you also have a way of providing a hard realtime timestamp (in our 
case a special
microcontroller board that watches the sensor trigger line), you may 
also provide this to the
TimestampEstimator. In this case the TimestampEstimator will try to 
estimate
the latency of the incoming data and compensate for it.

I hope this answered your questions
     Janosch

P.S.: Pierre, if anything I just said is bloody wrong, feel free to 
correct me ;-P

-- 
  Dipl. Inf. Janosch Machowinski
  SAR-&  Sicherheitsrobotik

  DFKI Bremen
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