[ODE] Curious behavior with a simple gravity example

jcwode@nym.hush.com jcwode at nym.hush.com
Wed Jan 24 23:27:19 MST 2007

Thanks Jon!

I figured it was some sort of misunderstanding on my part.  Another 
person did respond with a pretty informative link about first order 
Euler integrators.


So that answers my question about the slightly irregular values I 
was seeing for dWorldStep() and dWorldStepFast1().  But shouldn't 
the values from dWorldQuickStep() have also varied with the step 

>From my tests it seems that it acts as if I had only taken one 
giant step instead of many small steps. (ie. an acceleration of -10 
for 1 second results in a final displacement of -10)


(P.S. I hope this one is appended to the thread, rather than starts 
a new one)

On Wed, 24 Jan 2007 19:09:11 -0800 "Jon Watte (ODE)" <hplus-
ode at mindcontrol.org> wrote:
>jcwode at nym.hush.com wrote:
>> To me, this is a serious issue.  Why would a simple body, 
>> accelerated only by gravity, move differently depending on the 
>> resolution of the step taken when the total time covered by the 
>> steps is constant?
>ODE uses a first order integrator, much like most other game 
>engines you can find. This means that the integration result is 
>dependent on the size of the time step. This is one of the reasons 
>why a 
>fixed time step should always be used with ODE, or almost any 
>other game 
>physics library.
>          / h+

More information about the ODE mailing list