Quaternion issue

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Maci
Posts: 3
Joined: Mon Jul 15, 2019 8:30 am

Quaternion issue

Post by Maci » Tue Jul 23, 2019 1:09 pm

Hi all,
I have the following code fragment;

Code: Select all

            var body = new BodyReference(BodyHandle, characters.Simulation.Bodies);
            ref var pose = ref body.Pose;
            pose.Orientation = Quaternion.CreateFromYawPitchRoll(input.CameraAngle, 0, 0);
            Quaternion.TransformUnitZ(pose.Orientation, out var viewDirection);
            Quaternion.GetAxisAngleFromQuaternion(pose.Orientation, out var axis, out var angle);
            Console.WriteLine($"CS:{input.CameraAngle} VD:{viewDirection} A:{axis} ANGLE:{angle}");
I get the following sample output:
CS:90.15236 VD:<0.8156362, 0, -0.5785651> A:<0, 1, 0> ANGLE:2.187765
CS:96.18495 VD:<0.9336317, 0, -0.3582342> A:<0, 1, 0> ANGLE:1.937172
CS:128.3905 VD:<0.4029752, 0, -0.9152108> A:<0, 1, 0> ANGLE:2.726827
CS:144.3713 VD:<-0.1414784, 0, 0.9899414> A:<0, -1, 0> ANGLE:0.1419543

Why is my angle variable wildly different from input.CameraAngle? If I create a Quaternion using CreateFromYawPitchRoll() and then invoke Quaternion.GetAxisAngleFromQuaternion() shouldn't I get the same numbers?
I'm confused...

Maci

Norbo
Site Admin
Posts: 4885
Joined: Tue Jul 04, 2006 4:45 am

Re: Quaternion issue

Post by Norbo » Tue Jul 23, 2019 10:32 pm

Orientation quaternions don't distinguish between 2 * PI and 164 * PI, since they correspond to the same orientation. It's also worth noting that all angles are in terms of radians, not degrees.

Note that (128.3905 % PI) ~= 2.726827.

Maci
Posts: 3
Joined: Mon Jul 15, 2019 8:30 am

Re: Quaternion issue

Post by Maci » Wed Jul 24, 2019 7:08 am

I had completely missed that angles were in radians...
Shame on me...

Maci

Norbo
Site Admin
Posts: 4885
Joined: Tue Jul 04, 2006 4:45 am

Re: Quaternion issue

Post by Norbo » Wed Jul 24, 2019 9:19 pm

It's okay, you're not the first, nor will you be the last :P

lidgren
Posts: 21
Joined: Mon May 27, 2019 6:28 pm

Re: Quaternion issue

Post by lidgren » Mon Dec 23, 2019 1:23 am

Slightly related; what are the reason System.Numerics quaternion isn't used? It's a only a slight nuisance having to convert every time but still...

Norbo
Site Admin
Posts: 4885
Joined: Tue Jul 04, 2006 4:45 am

Re: Quaternion issue

Post by Norbo » Mon Dec 23, 2019 1:51 am

It's been a while since that decision was made- originally, there were some concerns about codegen around parameters and a couple of numerical issues, like in slerp corner cases.

It would not surprise me if the codegen concerns are lesser or gone now. There are still some functions not offered in the Numerics type, but that's pretty easy to handle without a full custom name-colliding type. So at this point, it's just because I haven't yet confirmed codegen quality and put in the time to do it.

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