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  Calculate stopping distance  (Read 1712 times)
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Offline Dreamcatchermatt

Junior Duke





« Posted 2010-05-13 16:33:45 »

As part of my waypoint following algorythem, I want my character to accellerate towards a waypoint untill it reaches a point (that should be half way) where it must start accellerateing in the opposite direction to stop in-time, landing on the waypoint.

My character has three Vector2D(double x, double y) vectors; position, velocity and acceleration.

currently my waypoint following logic is;
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// if there are waypoints left to go to
if(waypoints.Size() > 0)
{
    boolean x = NavigateToWaypoint(waypoints.Peek());
    if(x)
    {
        waypoints.Pop();
    }
     else
    {
        STOP();
    }
}


the STOP() method just sets the 'i am navigateing now' flag to false, stopping the Update() method for my navigation class from running.

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NavigateToWaypoint(Vector2D waypoint)
{
    if( // stopping distance > distance to waypoint)
    {
         // break by accellerateing in opposite direction to waypoint.
         return false;
    }
    else if( // stopping distance < distance to waypoint )
    {
        // accellerate towards waypoint ('ahead full impulse!')
        return false;
    }
    else if(distance to waypoint < 100)
    {
        // stop the ship, we're there
        return true;
    }
}


what i'm asking here is how to calculate the stopping distance X for velocity V at acceleration A.

I know its somthing similar to v(end) = v(start) * 2/AX but i'm also sure that this is not it Smiley

I used to know all these formuli back at school - now I cant for the life of me remember what it is, and serching around on google has got me lots of equations that are either way too complicated (wikipedia Tongue ) or not anything I recognise.

if theres any math guys out there who can gove me some hints that would be great.
Offline Eli Delventhal

JGO Kernel


Medals: 42
Projects: 11
Exp: 10 years


Game Engineer


« Reply #1 - Posted 2010-05-13 17:21:14 »

Have a look here:

http://www.java-gaming.org/topics/calculating-acceleration-and-decelleration-to-reach-a-certain-point-in-time/20093/view.html

I asked pretty much the same question towards the end of the thread.

See my work:
OTC Software
Offline Dreamcatchermatt

Junior Duke





« Reply #2 - Posted 2010-05-13 20:18:35 »

Ahhhhhhhh, yeh, that's the one i had half-remembered:

Yeah, that's the discrete (sampled) version of the formula pjt33 posted earlier: s = ut + (1/2)*at^2

The summation s(n-1) can be simplified to n(n-1)/2, and then the relation between the two equations becomes more obvious.

chears for that Smiley


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