(Java) Converting a Quaternion into Radians (Or Degrees)?

Question

I've been messing around in OpenGL, and JBullet for the last few days. After a lot of tinkering I finally managed to fix quite a few bugs in JBullet, and make it usable for some demos. Issue I'm currently having is I can't manage to convert the translation into Degrees, so far I've had the best results with Quaternions, to Radians with the following code:

public Vector3f getRadians(Quat4f quat) {
    Vector3f v = new Vector3f();
    //float scale = (float) Math.abs(quat.x * quat.y * quat.z); //Apparently the scale of the angle, thought without I get a almost perfect result on the X-Axis
    float angle = (float) Math.abs(Math.acos(quat.w)) * 2.0f;

    v.x = angle * Math.round(quat.x);
    v.y = angle * Math.round(quat.y);
    v.z = angle * Math.round(quat.z);               

    return v;
}

It's worth noting that my only success would be on the X-Axis of the Quaternion, and that's with no translation on any other axis. Not to mention it's off by anywhere from 0-6 Degrees.

Answer 1

I'm really not sure this is what you want, but from glm::gtx::quaternion :

inline valType roll
(
    detail::tquat<valType> const & q
)
{
    return atan2(valType(2) * (q.x * q.y + q.w * q.z), q.w * q.w + q.x * q.x - q.y * q.y - q.z * q.z);
}

template <typename valType> 
inline valType pitch
(
    detail::tquat<valType> const & q
)
{
    return atan2(valType(2) * (q.y * q.z + q.w * q.x), q.w * q.w - q.x * q.x - q.y * q.y + q.z * q.z);
}

template <typename valType> 
inline valType yaw
(
    detail::tquat<valType> const & q
)
{
    return asin(valType(-2) * (q.x * q.z - q.w * q.y));
}

So, in a more readable form :

float roll = atan2(valType(2) * (q.x * q.y + q.w * q.z), q.w * q.w + q.x * q.x - q.y * q.y - q.z * q.z);
float pitch = atan2(valType(2) * (q.y * q.z + q.w * q.x), q.w * q.w - q.x * q.x - q.y * q.y + q.z * q.z);
float yaw = asin(valType(-2) * (q.x * q.z - q.w * q.y));
vec3 EulerAngles = vec3(pitch, yaw, roll);