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 Sent: Wednesday, July 02, 2014 10:00 PM To: softimage@listproc.autodesk.com 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.
