Re: Aggressive tracking in a newtonian simulation

Hi Darren,

On Tue, 30 Nov 2010 22:48:55 +1300, Darren Grant  
<[email protected]> wrote:
>> I am a programmer tasked with developing a newtonian simulation of
>> high performance spacecraft.

For I-War 2, we had what sounds like a similar setup of rigid bodies and  
requirements. We used a very simple follower for each (local space)  
angular velocity component, basically the same as the linear velocity  
component. I just looked up the code and it was something like:

for each component i:
   dv[i] = target[i] * max_speed[i] - current[i]
   torque[i] = clamp_to_max_torque( dv[i] * moment[i] / dt )

(moment is the diagonal of the MoI matrix - all our stuff was in this form)

Pretty horrible stuff - especially dividing by dt - but it worked OK in  
practice. We didn't allow ridiculous speeds or torques. Our integrator was  
straight Euler, and while I thought it had some bespoke stuff in to stop  
it hunting or blowing up, I looked and couldn't find it. I'm sure I  
remember playing with this at some point, but maybe we ended up  
constraining the inputs such that it would remain stable.

For the NPC ships, our AI coder (Brett Laming) drove the same simulation  
by setting max angular/linear speeds. He went into more kinematic depth to  
figure out what inputs to use so that a ship would arrive at a particular  
place at a particular time (acceleration, coasting, braking). I suspect  
these days both of us might consider a less pure approach whereby the AI  
can get at the simulation at a lower level than the pilot interface so we  
wouldn't have to second-guess it so much.

Heh. While looking for this, I found the marvellously-named  
iiSim::DetachAndFlingChild. As a parent, I have to say I disapprove!

HTH,

Will

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