main/src/georegression/geometry/ConvertRotation3D_F64.java
public static DMatrixRMaj quaternionToMatrix( Quaternion_F64 quat, DMatrixRMaj R ) {
		return quaternionToMatrix(quat.w,quat.x,quat.y,quat.z,R);
	}
public static DMatrixRMaj quaternionToMatrix( Quaternion_F64 quat, DMatrixRMaj R ) {
		return quaternionToMatrix(quat.w,quat.x,quat.y,quat.z,R);
	}
<p>Converts a unit quaternion into a rotation matrix.</p>

<p>
Equations is taken from: Paul J. Besl and Neil D. McKay, "A Method for Registration of 3-D Shapes" IEEE
Transactions on Pattern Analysis and Machine Intelligence, Vol 14, No. 2, Feb. 1992
</p>

@param quat Unit quaternion.
@param R Storage for rotation matrix.  If null a new matrix is created. Modified.
@return Rotation matrix