[doctorWho]

Hi,


I am trying to figure out how the rigidBodyMeshMotion works.


What I am wondering is in the following statements


const septernion transform0(this->transform0(bodyIndex));
const scalarField& weight = bodyMeshes_[0].weight_;

forAll(points0, pointi)
{
// Don't move where weight ~= 0
if (weight[pointi] <= small)
{}
// Use solid-body motion where weight ~= 1
else if (weight[pointi] > 1 - small)
{
pointDisplacement[pointi] =
transform0.transformPoint(points0[pointi]) - points0[pointi];
}
// Slerp septernion interpolation
else
{
pointDisplacement[pointi] =
slerp(septernion::I, transform0, weight[pointi]).transformPoint(points0[pointi])
- points0[pointi];
}
}



the statement transform0.transformPoint(points0[pointi]) is from the quaterniaon class member function transformPoint(const vector& v) defined as follows:


inline Foam::vector Foam::septernion::transformPoint(const vector& v) const
{
return r().transform(v - t());
}



looking at this definition, the transformPoint is

1) move a point v to the rotation center by subtracting displacement t()
2) apply rotation tensor to have coordinate transformation


but this code does not have an operation to move the transformed point to the original position by translation t() as defined in transform member function of sixDoFRigidBodyMotion as follows:


Foam::tmp<Foam:ointField> Foam::sixDoFRigidBodyMotion::transform
(
const pointField& initialPoints
) const
{
return
(
centreOfRotation()
+ (Q() & initialQ_.T() & (initialPoints - initialCentreOfRotation_))
);
}





Anyone can explain how transformPoint works in rigidBodyMeshMotion?