submatrix (
        self,
        ijk_origin,
        ijk_size,
        )

Must overide this function in derived class to return a 3 dimensional Numeric Python matrix. The returned matrix has size ijk_size and element ijk is accessed as m[k,j,i]. It is an error if the requested submatrix does not lie completely within the full data matrix. It is also an error for the size to be <= 0 in any dimension. These invalid inputs might throw an exception or might return garbage. It is the callers responsibility to make sure the arguments are valid.