Utilizing PhysiJS for obtaining linear velocity at a specific point on a rotating object

Question

Utilizing PhysiJS for obtaining linear velocity at a specific point on a rotating object

Is there a way to calculate the linear velocity (relative to world space) of a point on an object in PhysiJS, utilizing the object's linear and angular velocity?

I considered creating an invisible vertex on the object for this task, but it seems like the API doesn't support that functionality. Do I have to manually calculate it based on the translational and rotational velocity of the object? (And if so, does THREE.js or PhysiJS provide a straightforward method for doing so?)

Starting from the basics:

Given object.position (1)
Given the position of the point in world space object.localToWorld(point) (2)
Given object.getLinearVelocity() (3)
Given object.getAngularVelocity() (4)

Therefore, I need to:

Subtract (1) from (2) to find the point's offset in world space (5)
Utilize (4) and (5) to determine the linear velocity of the point relative to the object (6)
Add (6) and (3) to obtain the total linear velocity of the point

To achieve the first and third steps, I can utilize Three.js's Vector3 methods .sub(Vector3) and .add(Vector3). However, the middle operation is challenging me, although I suspect it involves some form of multiplication. What operation should I employ, considering that (4) can be either a Euler angle or a Quaternion?

My familiarity with matrices is quite limited (and rusty!), and I have no experience with quaternions.

You can access Three.js's API documentation here.

Thank you!

javascript 3d three.js webgl physijs

Answer 1

Answer №1

Finally! Successfully resolved the issue. Here is a more versatile version that doesn't rely on PhysiJS. Simply replace the vectors with those from PhysiJS.

scene.add(point2);
scene.add(pointAxis);
pointAxis.add(point);

angularVelocity = new THREE.Vector3( 0, 0, 0.01);

function animate(){

    // rotate point around pointAxis
    pointAxis.rotation = pointAxis.rotation.add(angularVelocity);

    // calculate position of point in world space
    var pointPosWorld = pointAxis.localToWorld(point.position.clone());

    // calculate position of point in world relative to fulcrum
    var pointOffsetPos = new THREE.Vector3();
    pointOffsetPos = pointPosWorld.sub(pointAxis.position.clone());

    // Calculate tangential velocity
    tangentialVelocity = rotate.clone().cross(pointOffsetPos);

}

I reached this solution after finding guidance here on the physics stack exchange site.

Answer 2

Finally! Successfully resolved the issue. Here is a more versatile version that doesn't rely on PhysiJS. Simply replace the vectors with those from PhysiJS.

scene.add(point2);
scene.add(pointAxis);
pointAxis.add(point);

angularVelocity = new THREE.Vector3( 0, 0, 0.01);

function animate(){

    // rotate point around pointAxis
    pointAxis.rotation = pointAxis.rotation.add(angularVelocity);

    // calculate position of point in world space
    var pointPosWorld = pointAxis.localToWorld(point.position.clone());

    // calculate position of point in world relative to fulcrum
    var pointOffsetPos = new THREE.Vector3();
    pointOffsetPos = pointPosWorld.sub(pointAxis.position.clone());

    // Calculate tangential velocity
    tangentialVelocity = rotate.clone().cross(pointOffsetPos);

}

I reached this solution after finding guidance here on the physics stack exchange site.

Utilizing PhysiJS for obtaining linear velocity at a specific point on a rotating object

Answer №1

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