List<Matrix<? extends PArray>> expandedMatrices =
new ArrayList<Matrix<? extends PArray>>(actualFrames.size());
for (Frame<P> localFrame : actualFrames) {
Point o = localFrame.position().area().min();
IPoint localOffset = o.toRoundedPoint();
assert o.equals(localOffset.toPoint());
Matrix<? extends PArray> m = localFrame.matrix();
m = Matrices.asFuncMatrix(Func.IDENTITY, DoubleArray.class, m);
// - we need Double virtual matrix to provide correct NaN values to the combining function
m = m.subMatr(localOffset.symmetric().coordinates(), dimensions, Matrix.ContinuationMode.NAN_CONSTANT);
expandedMatrices.add(m);