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Re: [certi-dev] FlightGear simulation latency

From: Eric Noulard
Subject: Re: [certi-dev] FlightGear simulation latency
Date: Sat, 23 May 2009 15:15:20 +0200

2009/5/23 Martin Spott <address@hidden>:
> Hi Petr,
> "Gotthard, Petr" wrote:
>>> I just found out that using the RPR FOM (--hla=[...],RPR,RPR-FOM-
>>> v1.0.fed)
>>> induces just a fraction of the latency compared to using the ASN FOM
>>> (--hla=[...],ASN,AviationSimNet-v3.1.fed). In consequence, using the
>>> RPR FOM results in a latency which is similar to that of FlightGear's
>>> native MultiPlayer protocol.
>> Brilliant! I tell you why: The RPR FOM has entries for velocity and
>> acceleration, while the ASN does not. The native dead reckoning
>> algorithm thus works only for the RPR FOM, what makes the latency
>> similar to the native MultiPlayer.
> Oh yes, after re-reading through the different FOM's and the
> corresponding player-xxx files I was already suspecting such a
> correlation.
> I noticed that even RPR doesn't support angular acceleration -
> appparently the folks at SISO don't consider it to be meaningful for
> dead-reckoning in such a use case.

Concerning dead-reckoning for which I am quite a newbie,
could one of you explain how the distance between
"exact/high-fidelity position" and the "extrapolated position" is measured?

I mean the only entity which may compute this is the one which runs
the high-fidelity model, because otherwise it would require the packet
for which DR is precisely made for?

Am I right?

example: a simulation with 2 entity planeA and planeB
planeA is using DR for both the planeB data and its owns data
along with the 'high-fidelity" model for itself and then compare
the DR value for itself and the "high-fidelity value" and send
an update (to planeB) with new high-fidelity values when the
DR threshold is reached, is that right?

> Thanks for sharing your insight with me,
>        Martin.
> P.S.: If the CERTI folks feel uneasy about me polluting the list with
>      FlightGear-related stuff, please don't hesitate to complain.

No complain, we are learning :-)

The CERTI ML is not that high number of msg ML to be disturb with
user's application test case.


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