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 <mailto:[email protected]>
*Sent:* Wednesday, July 02, 2014 10:00 PM
*To:* [email protected]
<mailto:[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.
