Null Parameters and Changing FOV

Often the model of the underlying object is larger than the portion contained in the field of view of the image. In this case, the shapes $S_k$ that are outside the field of view will not appear in the image. This leads to zero columns in $G$ (the null space), and the parameters associated with these columns are the null parameters, $\alpha_{null}$, which can be easily marginalised (integrated over).