Smoothing out Noisey Input Data

sava nozin

Snap Lens Network Member Lens Studio Team

August 12, 2018 18:53
Edited

Hi,

I'm currently building something similar to animojis and require a way to smooth out the head tracking input values. I'm calculating velocity to control my blend shape weights. So far the system seems to work, but the input is sometimes very sporadic causing the animations to flicker:

I know it's possible to smooth out my values using the lerp function, but I can't seem to get it to work properly for the blendshape weights.

Relevant code snippet:

 currentRotation = script.objectTransform.getWorldRotation();
 var lerpedRotation = quat.slerp( currentRotation, script.attachToTransform.getWorldRotation(), script.rotSmoothing * getDeltaTime() ); 
 var lerpedEulerAngle = lerpedRotation.toEulerAngles();
 
 // calculate angular velocity
 var rotationDelta = lerpedEulerAngle.sub(rotationLast);
 rotationLast = lerpedEulerAngle;
 
 var twistWeight = rotationDelta.y / getDeltaTime() * 1;
 var tiltWeight = rotationDelta.z / getDeltaTime() * 1;
 
 
 script.blendShape.setBlendShape(script.tilt_left, clamp(tiltWeight, -1, 1));
 script.blendShape.setBlendShape(script.twist_left, clamp(twistWeight, -1, 1));

Thanks,

Sava

Jacob

Snap Lens Network Member Lens Studio Team

August 14, 2018 01:26

Hi Sava,

For rotations, it's usually better to work in quaternions than euler angles. You can do something like this to get the Y and Z angle deltas:

//@input SceneObject obj1
//@input SceneObject obj2

// Returns the delta quaternion
function getDiff(q1, q2){
 return q2.multiply(q1.invert());
}

// Returns Y rotation of a quaternion
function getYRot(q){
 return Math.atan(q.y, q.w);
}

// Returns Z rotation of a quaternion
function getZRot(q){
 return Math.atan(q.z, q.w);
}

var t1 = script.obj1.getTransform();
var t2 = script.obj2.getTransform();

var diff = getDiff(
 t1.getWorldRotation(), 
 t2.getWorldRotation()
);

print("y: " + getYRot(diff));
print("z: " + getZRot(diff));

Hope this helps! Looks like a really cool lens!

sava nozin
Snap Lens Network Member Lens Studio Team

August 15, 2018 13:25

Edited
Hey! That works! Never thought I'd learn a useful math lesson on how Euler coordinates aren't reliable for rotation lol. My one concern is this method seems fairly resource intensive. Are there any computationaly cheap ways to approximate the Y/Z components without using arctan?

Edit: I want to use the following formula:

I'm just a little uncertain what the function does with q.z, comma q.w. is it simply arcatan(q.z/q.w)?
```
Math.atan(q.z, q.w)
```
Comment actions Permalink
Jonathan Solichin
Snap Lens Network Member Lens Studio Team

August 16, 2018 18:22
Hi Sava!

Glad you're thinking about performance! Did you see some performance slow down when you used it?

The Math.atan function is actually the built in javascript function: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/atan2.

The first argument is the Y coordinate, and the second is the X coordinate of a point, where the arctan is the (counter clockwise) angle to the (positive) x axis (between -PI, PI).

Can't wait to see the result! Looks awesome!

Jon
Comment actions Permalink
sava nozin
Snap Lens Network Member Lens Studio Team

August 16, 2018 21:47
When I initially tried it the frame rate seems low, but after I restarted the app, it was running smooth. I guess I'll keep Math.atan for now, and figure out a cheap approximation later, if the need arises.

Thanks for all the help guys,

Sava
Comment actions Permalink

Smoothing out Noisey Input Data

We're here to help! We just need a little bit of information...

What system do you run Lens Studio on?

Follow the next steps to help us solve your issue:

Thanks for submitting this issue.

We'll try to resolve this issue as soon as possible. Thanks for letting us know about it!