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Re: [certi-dev] CERTI billard test / http_proxy

From: Martin Spott
Subject: Re: [certi-dev] CERTI billard test / http_proxy
Date: Fri, 22 May 2009 20:59:16 +0000 (UTC)
User-agent: tin/1.9.3-20080506 ("Dalintober") (UNIX) (Linux/ (x86_64))

Hi Petr,

"Gotthard, Petr" wrote:

>> My hopes with CERTI/HLA as an infrastructure for multi-instance
>> simulation (aka 'MultiPlayer' ;-)  is to have proper synchronization
>> among the involved instances on a local network, thus to reduce
>> latency.
> I'm not sure. Could you please be more specific on how a synchronization
> could reduce the latency?

Ah, sorry, I didn't intend to assert that just adding synchronization
would lead to reduced latency. Nevertheless I think it might help to do
so. As far as I can remember, there have been several approaches to
synchronize different instances in a simulation framework which make
use of extrapolation - including but not limited to the venerable DIS
protocol (please tell me if I'm wrong).

I suspect that the general technique is to send a packet which includes
positional data as well as velocities and forces plus a time stamp and
to let the reciever extrapolate how the vehicle would move at timestamp
+ dt. I know, this might fail for aircraft which are turning extremely
fast, but it might be a reasonable start. If I remember correctly, even
the current FlightGear MultiPlayer protocol is using such technique -
in order to work around network latency and drop-outs. I'm certain that
our CERTI folks also have a few comments to add.

I have to admit that I neither managed to understand where you're
picking up the positional data of the local instance to be fed into the
Federation nor that I understood how you're feeding remote aircraft
into the local instance. Ok, I didn't try too hard, but I think I'll
manage to get there.
Getting faster acces to these resource might help as well and if you
don't object, I'll get in touch with the respective subsystem
maintainers and try to direct their toughts to you.

> Implementing the features like flaps, lights or landing gear would be
> very simple if there was a mapping between the FlightGear properties and
> the ASN FOM http://www.aviationsimnet.com/doc/aviationsimnetV3.1.html
> Aren't you by any chance an expert on FlightGear properties? ;-) The
> properties are not as simple as I thought.

Yup, I think I've well understood that supporting these features is
mostly done by just adding the respective mappings. I guess I'm able to
help here as I'm quite familiar with the respective properties. Yet I'd
say (just my personal opinion) that there are more substantial issues
to deal with.

 Unix _IS_ user friendly - it's just selective about who its friends are !

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