Normalize the left 3x3 submatrix of this matrix.
<p>
The resulting matrix will map unit vectors to unit vectors, though a pair of orthogonal input unit
vectors need not be mapped to a pair of orthogonal output vectors if the original matrix was not orthogonal itself
(i.e. had <i>skewing</i>).
Normalize the left 3x3 submatrix of this matrix. <p> The resulting matrix will map unit vectors to unit vectors, though a pair of orthogonal input unit vectors need not be mapped to a pair of orthogonal output vectors if the original matrix was not orthogonal itself (i.e. had <i>skewing</i>).
@return this