Algorithm 1. Improved quadtree-based feature points’ uniform distribution algorithm

Input: image sequence

Output: saved ORB feature points Kp

1: Build image pyramid

2: Extract Fast features by adaptive threshold

3: for every pyramid layer l do

4:   divide the quadtree node on the l layer pyramid

5:   while d←0 < maxD do

6:    for every child node i do

7:     if nNum(i) > 1 && !noFlag(i) do

8:       divide the child quadtree node in the parent i node

9:     else

10:      noFlag(i) = 1

11:      end if

12:     end for

13:     d++

14:   end while

15:   Sort features in every divided node from large to small according to Harris response value

16:   while Kp < DesFi do

17:     for every node i do

18:      if nNum(i) > 1&& maxkp > minH do

19:       add maxkp to Kp and erase it in the i node

20:      end if

21:     end for

22:    end while

23: end for