Closing the loop
	Problem • requires good tracked features as input Can we use SFM to help track points? • basic idea:  recall form of Lucas-Kanade equation: • with n points in f frames, we can stack into a big matrix
		Matrix on RHS has rank <= 3 !! • use SVD to compute a rank 3 approximation • has effect of filtering optical flow values to be consistent • [Irani 99]