You introduced a magnitude to the velocity which will over time amount to further distance, but reasoned the problem out without that variable. It would work if the velocity was infinitely small.
Multiplying that vector you pump into the velocity by an extremely small number should reduce the slingout, until you hit precision limits and you end up with an immobile object because the velocity drops to 0, but for the right combination of numbers it might stay subpixel for long enough to be "artistically" the result you want. If you needed it for a practical application you would of course be better off rotating the vector around y instead, affecting angular velocity instead of linear won't compromise the system and will give you the result you want. On Fri, Jul 4, 2014 at 4:21 AM, olivier jeannel <[email protected]> wrote: > Ah, thank's for clarifying this. Makes perfect sense. > > Le 03/07/2014 11:34, [email protected] a écrit : > > this does make sense to me, if I think of it as a rocket orbiting a > planet. > > at each moment in time the rocket is pushing itself forward with a linear > force (the vector) - so it will tend to move from where it is to where the > force is telling it to go – in a straight line, tangent to the circle you > are after – but it already has it’s current speed, so you don’t end up > exactly where you are pointing but a bit further out - leaving the circle a > bit. The next moment in time you are correcting with the new tangent vector > – so you are approximately following the circle. > > if you want to get the perfect circle, you will need to add another force, > pulling towards the centre. ( check on centripetal force: > http://en.wikipedia.org/wiki/Centripetal_force ) > in ice: subtract the pointposition from the center of the circle and > multiply by scalar to finetune – add this vector to the one you have > In the example of the orbiting rocket I guess that would be gravity. > > > > > > > *From:* olivier jeannel <[email protected]> > *Sent:* Wednesday, July 02, 2014 10:00 PM > *To:* [email protected] > *Subject:* Running in circle, The CrossProduct question > > Hi gang, > > with my partner we were discussing crossproduct "theory" and I'm not sure > what to believe or think. > > I was persuaded that the result of a Cross Product of a PointPosition > (x,y,z) and a vector 0,1,0 plugged in a the PointVelocity, would give a > particle orbiting around 0,0,0 describing a perfect circle. > > In fact, not exactly. > > with simulation substep 1 I get this : > > > with simulation substep 10 I get this (but it travels much slower) : > > > So my question is : Is this a problem of approximation from the or the > computer, and then the mathematical nature of cross product is able to > "describe" a circle. > > or is this a normal behaviour, considering that the cross product vector > is pushing in straight line a particle and that it could never "describe" a > circle. > > > > -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are!
