ttp://java.sun.com/products/java-media/3D/forDevelopers/J3D_1_3_API/j3dapi/javax/vecmath/GVector.html
>void mul(GMatrix m1, GVector v1)
> Multiplies matrix m1 times Vector v1 and places the result into this vector (this = m1*v1).
>int getSize()
> Returns the number of elements in this vector.
>double getElement(int index)
> Retrieves the value at the specified index value of this vector.
試してないけど、このあたりでできんじゃない？