public static MatrixD BSpline(MatrixD a, MatrixD b, float t)
{
var up = Vector3D.Lerp(a.Up, b.Up, t);
var bez = new CubicCurve(a, b);
var x = bez.Sample(t);
var fwd = bez.SampleDerivative(t);
return(MatrixD.CreateWorld(x, Vector3D.Normalize(fwd), Vector3D.Normalize(up)));
}
public Vector3D SampleDerivative(float t)
{
return(Vector3D.TransformNormal(
SphericalExtensions.DifferentialFromSpherical(_curve.Sample(t), _curve.SampleDerivative(t)), _matrix));
}