public ParallelPiped(Vector pmin, Vector vx, Vector vy, Vector vz, Material material) {
		super();
		this.pmin = pmin;
		this.material = material;
		pmax = pmin.add(vx).add(vy).add(vz);
		nx = vy.cross(vz).norm();
		ny = vz.cross(vx).norm();
		nz = vx.cross(vy).norm();
	}