Quaternion "lookAt" function
Date : March 29 2020, 07:55 AM
seems to work fine Im struggling with the following problem. Im working with bone animation and I want (ie) the head of the player to follow an another object in space. My up axis is +Z my forward axis is +Y, and the magnitude of the quaternion is in W. I tried to use the mesa code for gluLookAt and use the 3x3 matrix to transform to a quaternion but it doesn't work as expected so I go in another direction... , I think this function will do what you need: /// <summary>
/// Evaluates a rotation needed to be applied to an object positioned at sourcePoint to face destPoint
/// </summary>
/// <param name="sourcePoint">Coordinates of source point</param>
/// <param name="destPoint">Coordinates of destionation point</param>
/// <returns></returns>
public static Quaternion LookAt(Vector3 sourcePoint, Vector3 destPoint)
{
Vector3 forwardVector = Vector3.Normalize(destPoint  sourcePoint);
float dot = Vector3.Dot(Vector3.forward, forwardVector);
if (Math.Abs(dot  (1.0f)) < 0.000001f)
{
return new Quaternion(Vector3.up.x, Vector3.up.y, Vector3.up.z, 3.1415926535897932f);
}
if (Math.Abs(dot  (1.0f)) < 0.000001f)
{
return Quaternion.identity;
}
float rotAngle = (float)Math.Acos(dot);
Vector3 rotAxis = Vector3.Cross(Vector3.forward, forwardVector);
rotAxis = Vector3.Normalize(rotAxis);
return CreateFromAxisAngle(rotAxis, rotAngle);
}
// just in case you need that function also
public static Quaternion CreateFromAxisAngle(Vector3 axis, float angle)
{
float halfAngle = angle * .5f;
float s = (float)System.Math.Sin(halfAngle);
Quaternion q;
q.x = axis.x * s;
q.y = axis.y * s;
q.z = axis.z * s;
q.w = (float)System.Math.Cos(halfAngle);
return q;
}

Handling Quaternion "LookAt" function  Keeping the character upright
Date : March 29 2020, 07:55 AM
hope this fix your issue Such kind of operation better to perform with matrixes Calculating a LookAt matrixThan convert back to quaternion.

Quaternion to EulerXYZ, how to differentiate the negative and positive quaternion
Tag : cpp , By : Sascha Brossmann
Date : March 29 2020, 07:55 AM
it fixes the issue The quaternions q and q are different; however, the rotations represented by the two quaternions are identical. This phenomenon is usually described by saying quaternions provide a double cover of the rotation group SO(3). The algebra to see this is very simple: given a vector represented by quaternion p, and a rotation represented represented by a quaternion q, the rotation is qpq^{1}. On the other hand, qp(q)^{1} = 1qp(q)^{1}(1) = q(1)p(1)q^{1} = qp(1)^2q^{1} = qpq^{1}, the same rotation. Quaternions normally don't commute, so pq != qp for general quaternions, but scalars like 1 do commute with quaternions. I believe ToEulerXYZ should be the same in both cases, which it appears to be.

Converting glm::lookat matrix to quaternion and back
Tag : cpp , By : Jim Davis
Date : November 24 2020, 05:44 AM

Cesium JS flying to camera.lookAt (Migrating from Google Earth Plugin API lookAt)
Date : March 29 2020, 07:55 AM

