Conversion between Euler <=> Quaternion like in Unity3d engine

Question

I\'ve used two examples (from this site too), but results are not the same as those that said Unity.

Quaternion.Euler and .eulerAngles are Unity functions. FromQ doe

Answer 1

Here's my solution. This is very very close to Unity's Quaternion.Euler and quaternion.eulerAngles. The discrepancies are small enough that they shouldn't matter for any application.

public static Vector3 QuaternionToEuler(Quaternion q)
{
    Vector3 euler;

    // if the input quaternion is normalized, this is exactly one. Otherwise, this acts as a correction factor for the quaternion's not-normalizedness
    float unit = (q.x * q.x) + (q.y * q.y) + (q.z * q.z) + (q.w * q.w);

    // this will have a magnitude of 0.5 or greater if and only if this is a singularity case
    float test = q.x * q.w - q.y * q.z;

    if (test > 0.4995f * unit) // singularity at north pole
    {
        euler.x = Mathf.PI / 2;
        euler.y = 2f * Mathf.Atan2(q.y, q.x);
        euler.z = 0;
    }
    else if (test < -0.4995f * unit) // singularity at south pole
    {
        euler.x = -Mathf.PI / 2;
        euler.y = -2f * Mathf.Atan2(q.y, q.x);
        euler.z = 0;
    }
    else // no singularity - this is the majority of cases
    {
        euler.x = Mathf.Asin(2f * (q.w * q.x - q.y * q.z));
        euler.y = Mathf.Atan2(2f * q.w * q.y + 2f * q.z * q.x, 1 - 2f * (q.x * q.x + q.y * q.y));
        euler.z = Mathf.Atan2(2f * q.w * q.z + 2f * q.x * q.y, 1 - 2f * (q.z * q.z + q.x * q.x));
    }

    // all the math so far has been done in radians. Before returning, we convert to degrees...
    euler *= Mathf.Rad2Deg;

    //...and then ensure the degree values are between 0 and 360
    euler.x %= 360;
    euler.y %= 360;
    euler.z %= 360;

    return euler;
}

public static Quaternion EulerToQuaternion(Vector3 euler)
{
    float xOver2 = euler.x * Mathf.Deg2Rad * 0.5f;
    float yOver2 = euler.y * Mathf.Deg2Rad * 0.5f;
    float zOver2 = euler.z * Mathf.Deg2Rad * 0.5f;

    float sinXOver2 = Mathf.Sin(xOver2);
    float cosXOver2 = Mathf.Cos(xOver2);
    float sinYOver2 = Mathf.Sin(yOver2);
    float cosYOver2 = Mathf.Cos(yOver2);
    float sinZOver2 = Mathf.Sin(zOver2);
    float cosZOver2 = Mathf.Cos(zOver2);

    Quaternion result;
    result.x = cosYOver2 * sinXOver2 * cosZOver2 + sinYOver2 * cosXOver2 * sinZOver2;
    result.y = sinYOver2 * cosXOver2 * cosZOver2 - cosYOver2 * sinXOver2 * sinZOver2;
    result.z = cosYOver2 * cosXOver2 * sinZOver2 - sinYOver2 * sinXOver2 * cosZOver2;
    result.w = cosYOver2 * cosXOver2 * cosZOver2 + sinYOver2 * sinXOver2 * sinZOver2;

    return result;
}

Answer 2

This might only be worth a partial answer but here is "ToQ() = Quaternion.Euler()":

public static Quaternion ToQ(Vector3 v)
{
    return ToQ(v.y,v.x,v.z);
}

public static Quaternion ToQ(float yaw, float pitch, float roll)
{
    yaw*=Mathf.Deg2Rad;
    pitch*=Mathf.Deg2Rad;
    roll*=Mathf.Deg2Rad;
    float rollOver2 = roll * 0.5f;
    float sinRollOver2 = (float)Math.Sin((double)rollOver2);
    float cosRollOver2 = (float)Math.Cos((double)rollOver2);
    float pitchOver2 = pitch * 0.5f;
    float sinPitchOver2 = (float)Math.Sin((double)pitchOver2);
    float cosPitchOver2 = (float)Math.Cos((double)pitchOver2);
    float yawOver2 = yaw * 0.5f;
    float sinYawOver2 = (float)Math.Sin((double)yawOver2);
    float cosYawOver2 = (float)Math.Cos((double)yawOver2);
    Quaternion result;
    result.w = cosYawOver2 * cosPitchOver2 * cosRollOver2 + sinYawOver2 * sinPitchOver2 * sinRollOver2;
    result.x = cosYawOver2 * sinPitchOver2 * cosRollOver2 + sinYawOver2 * cosPitchOver2 * sinRollOver2;
    result.y = sinYawOver2 * cosPitchOver2 * cosRollOver2 - cosYawOver2 * sinPitchOver2 * sinRollOver2;
    result.z = cosYawOver2 * cosPitchOver2 * sinRollOver2 - sinYawOver2 * sinPitchOver2 * cosRollOver2;

    return result;
} 

The 'FromQ' part of your question is a different matter. Euler angle comparison is a pain in the behind.

Answer 3

I've found solution

public static Quaternion ToQ (Vector3 v)
{
    return ToQ (v.y, v.x, v.z);
}

public static Quaternion ToQ (float yaw, float pitch, float roll)
{
    yaw *= Mathf.Deg2Rad;
    pitch *= Mathf.Deg2Rad;
    roll *= Mathf.Deg2Rad;
    float rollOver2 = roll * 0.5f;
    float sinRollOver2 = (float)Math.Sin ((double)rollOver2);
    float cosRollOver2 = (float)Math.Cos ((double)rollOver2);
    float pitchOver2 = pitch * 0.5f;
    float sinPitchOver2 = (float)Math.Sin ((double)pitchOver2);
    float cosPitchOver2 = (float)Math.Cos ((double)pitchOver2);
    float yawOver2 = yaw * 0.5f;
    float sinYawOver2 = (float)Math.Sin ((double)yawOver2);
    float cosYawOver2 = (float)Math.Cos ((double)yawOver2);
    Quaternion result;
    result.w = cosYawOver2 * cosPitchOver2 * cosRollOver2 + sinYawOver2 * sinPitchOver2 * sinRollOver2;
    result.x = cosYawOver2 * sinPitchOver2 * cosRollOver2 + sinYawOver2 * cosPitchOver2 * sinRollOver2;
    result.y = sinYawOver2 * cosPitchOver2 * cosRollOver2 - cosYawOver2 * sinPitchOver2 * sinRollOver2;
    result.z = cosYawOver2 * cosPitchOver2 * sinRollOver2 - sinYawOver2 * sinPitchOver2 * cosRollOver2;

    return result;
}

public static Vector3 FromQ2 (Quaternion q1)
{
    float sqw = q1.w * q1.w;
    float sqx = q1.x * q1.x;
    float sqy = q1.y * q1.y;
    float sqz = q1.z * q1.z;
    float unit = sqx + sqy + sqz + sqw; // if normalised is one, otherwise is correction factor
    float test = q1.x * q1.w - q1.y * q1.z;
    Vector3 v;

    if (test>0.4995f*unit) { // singularity at north pole
        v.y = 2f * Mathf.Atan2 (q1.y, q1.x);
        v.x = Mathf.PI / 2;
        v.z = 0;
        return NormalizeAngles (v * Mathf.Rad2Deg);
    }
    if (test<-0.4995f*unit) { // singularity at south pole
        v.y = -2f * Mathf.Atan2 (q1.y, q1.x);
        v.x = -Mathf.PI / 2;
        v.z = 0;
        return NormalizeAngles (v * Mathf.Rad2Deg);
    }
    Quaternion q = new Quaternion (q1.w, q1.z, q1.x, q1.y);
    v.y = (float)Math.Atan2 (2f * q.x * q.w + 2f * q.y * q.z, 1 - 2f * (q.z * q.z + q.w * q.w));     // Yaw
    v.x = (float)Math.Asin (2f * (q.x * q.z - q.w * q.y));                             // Pitch
    v.z = (float)Math.Atan2 (2f * q.x * q.y + 2f * q.z * q.w, 1 - 2f * (q.y * q.y + q.z * q.z));      // Roll
    return NormalizeAngles (v * Mathf.Rad2Deg);
}

static Vector3 NormalizeAngles (Vector3 angles)
{
    angles.x = NormalizeAngle (angles.x);
    angles.y = NormalizeAngle (angles.y);
    angles.z = NormalizeAngle (angles.z);
    return angles;
}

static float NormalizeAngle (float angle)
{
    while (angle>360)
        angle -= 360;
    while (angle<0)
        angle += 360;
    return angle;
}

Answer 4

This question is almost three years old, but I needed the same code and the ones posted here seemed to be incorrect, so I tweaked them and found this:

public static Quaternion Euler(float yaw, float pitch, float roll) {
        yaw*=Mathf.Deg2Rad;
        pitch*=Mathf.Deg2Rad;
        roll*=Mathf.Deg2Rad;

        double yawOver2 = yaw * 0.5f;
        float cosYawOver2 = (float)System.Math.Cos(yawOver2);
        float sinYawOver2 = (float)System.Math.Sin(yawOver2);
        double pitchOver2 = pitch * 0.5f;
        float cosPitchOver2 = (float)System.Math.Cos(pitchOver2);
        float sinPitchOver2 = (float)System.Math.Sin(pitchOver2);
        double rollOver2 = roll * 0.5f;
        float cosRollOver2 = (float)System.Math.Cos(rollOver2);
        float sinRollOver2 = (float)System.Math.Sin(rollOver2);            
        Quaternion result;
        result.w = cosYawOver2 * cosPitchOver2 * cosRollOver2 + sinYawOver2 * sinPitchOver2 * sinRollOver2;
        result.x = sinYawOver2 * cosPitchOver2 * cosRollOver2 + cosYawOver2 * sinPitchOver2 * sinRollOver2;
        result.y = cosYawOver2 * sinPitchOver2 * cosRollOver2 - sinYawOver2 * cosPitchOver2 * sinRollOver2;
        result.z = cosYawOver2 * cosPitchOver2 * sinRollOver2 - sinYawOver2 * sinPitchOver2 * cosRollOver2;

        return result;
}

According to a few quick tests, this matches Quaternion.Euler 100%