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Convert Global Velocity to Local Velocity

by Demolishun · in Torque Game Engine · 10/22/2005 (1:11 pm) · 6 replies



Sorry, that is my head hitting the table a few times. This problem is driving me nuts. Here is my question:
Is there an way to convert the mRigid.linVelocity to vehicle local x, y , z velocities?
I am trying to rewrite the wheeledVehicle code to use "cheater" physics and need to be able to treat linear and rotational velocities with respect to the vehicle and not the world. I have messed with transforms and the like, but came to conclusion that I need to use the vehicle rotation somehow and not the vehicle position.

Thanks,
Frank Carney

P.S. I did not post in the public physics section because I expect to post engine code.
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Torque Owner Demolishun
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    Torque 3D Owner Stephen Zepp
    #1
    10/22/2005 (2:56 pm)
    There are two transforms that are part of Shapebase called mObjToWorld and mWorldToObj. These are used by the engine in various places to do what you are looking for as far as I am aware. You may want to search for them to get a feel for how they interact. Player.cc, pickAnimationThread() might be a good place to start!

    There isn't much documentation on how exactly they get used, but I'm working on it!

    Torque Owner Demolishun
    DemolishunConsulting Rocks!
    #2
    10/22/2005 (3:24 pm)
    Great! I will look into it.

    Torque Owner Demolishun
    DemolishunConsulting Rocks!
    #3
    10/22/2005 (3:41 pm)
    Here is how you do it:

    VectorF  vel;
mWorldToObj.mulV(mRigid.linVelocity,&vel);

    Note: The "vel" has to be a VectorF of default value, a Point3F will NOT work. Must be the way it is initialized.
    DOH! Okay, it can be a Point3F since in mPoint.h:
    typedef Point3F VectorF;

    Thanks, this dang engine is full of everything! Now I need to test this on a rotational velocity.

    Stay tuned,
    Frank

    Torque 3D Owner Stephen Zepp
    #4
    10/22/2005 (5:08 pm)
    I would suspect (haven't checked) that overloading will mean that you can't do a Point3FVariable->len(), which returns the magnitude of the vector. There are probably a few other minor aspects that a VectorF gives you that a Point3F doesn't.

    Torque Owner Mike Kuklinski
    #5
    10/22/2005 (9:04 pm)
    You can do Point3F->len()... they are really the exact same thing... I rarely use VectorF...

    Torque 3D Owner Scott Richards
    #6
    10/23/2005 (12:05 am)
    It's not overloading. Think of it instead as an alias. VectorF is another name for Point3F. Use either, as they are completely interchangeable. I use VectorF when the values represent a vector, and Point3F when they represent a point. eg: VectorF myVelocity v.s. Point3F myPosition. Just makes the code read better, in my opinion.

    In regards to the original topic, I'd like to point out that while there's no difference between a Point3F and a VectorF, there is a difference between MatrixF::mulP (typically for rotating and translating points) and MatrixF::mulV (typically for rotating vectors; note the lack of translation).