Re: Running in circle, The CrossProduct question
Hi Raffael, Out of curiosity, do you have an example of how you work with angular velocity ? Never tried that before. For example right now, I've built a tornado mostly based on CrossProduct. It's superb, but let's say the client want's it to turn faster, with a multiplied CrossProduct the particle will go away from the center (unless I add a vector to suck it back to the center (Centripetal) ). With an angularVelocity, do I have the possibility to just make it spin faster ? Le 04/07/2014 03:29, Raffaele Fragapane a écrit : 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 olivier.jean...@noos.fr mailto:olivier.jean...@noos.fr wrote: Ah, thank's for clarifying this. Makes perfect sense. Le 03/07/2014 11:34, pete...@skynet.be mailto:pete...@skynet.be 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:olivier.jean...@noos.fr *Sent:* Wednesday, July 02, 2014 10:00 PM *To:* softimage@listproc.autodesk.com mailto: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. -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are!
Re: Running in circle, The CrossProduct question
Sorry, I re-red in one of my own old post that Angular velocity is RBD only.. Le 04/07/2014 11:33, olivier jeannel a écrit : Hi Raffael, Out of curiosity, do you have an example of how you work with angular velocity ? Never tried that before. For example right now, I've built a tornado mostly based on CrossProduct. It's superb, but let's say the client want's it to turn faster, with a multiplied CrossProduct the particle will go away from the center (unless I add a vector to suck it back to the center (Centripetal) ). With an angularVelocity, do I have the possibility to just make it spin faster ? Le 04/07/2014 03:29, Raffaele Fragapane a écrit : 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 olivier.jean...@noos.fr mailto:olivier.jean...@noos.fr wrote: Ah, thank's for clarifying this. Makes perfect sense. Le 03/07/2014 11:34, pete...@skynet.be mailto:pete...@skynet.be 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:olivier.jean...@noos.fr *Sent:* Wednesday, July 02, 2014 10:00 PM *To:* softimage@listproc.autodesk.com mailto: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. -- Our users will know fear and cower before our software! Ship it! Ship it and let them flee like the dogs they are!
Re: Running in circle, The CrossProduct question
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.
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.
