/// <summary>
/// Get the FRotator representation of this Quaternion.
/// </summary>
public FRotator Rotator()
{
DiagnosticCheckNaN();
float singularityTest = Z * X - W * Y;
float yawY = 2.0f * (W * Z + X * Y);
float yawX = (1.0f - 2.0f * (FMath.Square(Y) + FMath.Square(Z)));
// reference
// http://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles
// http://www.euclideanspace.com/maths/geometry/rotations/conversions/quaternionToEuler/
// this value was found from experience, the above websites recommend different values
// but that isn't the case for us, so I went through different testing, and finally found the case
// where both of world lives happily.
const float singularityThreshold = 0.4999995f;
const float radToDeg = (180.0f) / FMath.PI;
FRotator rotatorFromQuat;
if (singularityTest < -singularityThreshold)
{
rotatorFromQuat.Pitch = -90.0f;
rotatorFromQuat.Yaw = FMath.Atan2(yawY, yawX) * radToDeg;
rotatorFromQuat.Roll = FRotator.NormalizeAxis(-rotatorFromQuat.Yaw - (2.0f * FMath.Atan2(X, W) * radToDeg));
}
else if (singularityTest > singularityThreshold)
{
rotatorFromQuat.Pitch = 90.0f;
rotatorFromQuat.Yaw = FMath.Atan2(yawY, yawX) * radToDeg;
rotatorFromQuat.Roll = FRotator.NormalizeAxis(rotatorFromQuat.Yaw - (2.0f * FMath.Atan2(X, W) * radToDeg));
}
else
{
rotatorFromQuat.Pitch = FMath.FastAsin(2.0f * (singularityTest)) * radToDeg;
rotatorFromQuat.Yaw = FMath.Atan2(yawY, yawX) * radToDeg;
rotatorFromQuat.Roll = FMath.Atan2(-2.0f * (W * X + Y * Z), (1.0f - 2.0f * (FMath.Square(X) + FMath.Square(Y)))) * radToDeg;
}
rotatorFromQuat.DiagnosticCheckNaN("FQuat::Rotator(): Rotator result " + rotatorFromQuat + " contains NaN! Quat = " + this.ToString() +
", YawY = " + yawY + ", YawX = " + yawX);
return(rotatorFromQuat);
}
