Re: Network prediction algorithms specific to racing?

Shawn Hargreaves wrote on his blog about having a track-space coordinate
system in MotoGP:

blogs.msdn.com/shawnhar/archive/2009/12/30/motogp-ai-coordinate-systems.aspx

<http://blogs.msdn.com/shawnhar/archive/2009/12/30/motogp-ai-coordinate-systems.aspx>If
you were to have the player's position and velocity transmitted in track
space coordinates instead of world space, you'd be able to do dead reckoning
in that space entirely - i.e. reckon forward based on the player's local
track velocity rather than their world space velocity. As long as the player
is on the track and not, say, driving perpendicular to it, the player would
always interpolate along the track, even on corners.

Corners are likely to be, quite literally, one of your corner cases, due to
players needing to slow down to corner correctly - something the
reckoning/interpolation would need to take into account. Additionally, if
the player is driving fast diagonally across the track, there may be cases
where he would be reckoned outside of the track, in which case you might
need to detect those cases and switch to a world space prediction method.

- Blair

On Fri, Apr 16, 2010 at 7:50 AM, Megan Fox <[email protected]> wrote:

> At present, we have a fairly terrible scheme that amounts to no real
> rectification or prediction AND a dead-space that allows out-of-sync
> conditions to get around how jumpy it would be without it.  Not so
> good.  I was pulled off my other tasks and re-assigned to make it not
> suck / take it to polished instead of prototype, basically.
>
> My suspicion is that dead reckoning (ie. like you say, simple
> extrapolation from last known pos/vel) will be "ok", but that it will
> tend to not produce the smooth arcs I'd like to see in a cart racer.
> I'm also not convinced that a second or third degree prediction from
> sampling the prior positions would be anywhere near usable if the
> player ever deviated from smooth arc driving.  So, just thought I'd
> see if there were any particular known-better-case solutions, given
> that it's a well-trodden domain.
>
> On Thu, Apr 15, 2010 at 3:25 PM, Jason Hughes
> <[email protected]> wrote:
> > I guess there are two aspects of this: prediction and visual
> rectification.
> >
> > We've been doing a networked basketball game recently, where one team is
> > entirely controlled remotely.  Even with fairly high latency, slow
> > moving objects (like players) will look okay using a smooth
> > rectification algorithm, but they're a little delayed from real-time.
> > High velocity objects  (ie. bullets or ballistic objects) are pretty
> > easy to sync as well, provided they are not controlled or intelligent.
> > The main issues we've had thus far involve rectifying the ball physical
> > state after a collision with a player, since that's often incorrect and
> > delayed.  Luckily, most collisions in basketball games result in the
> > ball being grabbed, so this isn't always an issue.  For reference, our
> > simple rectification code is X = Lerp(X, X', f), where f could vary
> > depending on the latency and current error.  Spline rectification would
> > be nicer, and we might implement that, though it may be overkill for us.
> >
> > I haven't tried prediction beyond simple linear extrapolation based on
> > the last single sample (position, velocity, orientation).  1st order
> > prediction would likely close most of the gaps for generally smooth
> > functions like position and orientation, but for velocity, I'm not sure
> > it would help in our case, since the velocity is basically joystick
> > angle for us and is generally discontinuous.
> >
> > Sorry I can't be more help with racing specifically.  Out of curiosity,
> > what have you tried and how did it work?
> >
> > Thanks,
> > JH
> >
> > Jason Hughes
> > President
> > Steel Penny Games, Inc.
> > Austin, TX
> >
> >
> > On 4/15/2010 3:34 PM, Megan Fox wrote:
> >> I'm currently fiddling with dead reckoning for a racing game I'm
> >> working on, but this seems like a specific enough domain that there
> >> ought to be specific-to-racing prediction approaches.  We have a
> >> fairly good idea of what the player is doing (trying to stay on the
> >> track), and that would seem to give more data that isn't really being
> >> exploited with standard approaches - but googling isn't turning up
> >> much.
> >>
> >> Do such algorithms exist?  Or, in practice, are the same approaches
> >> used in FPSes et al still the ones to use here?
> >>
> >>
> >
> >
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>
> --
> Megan Fox
> http://www.shalinor.com/
>
>
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