## ← 18-01 Structure From Motion Question

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Showing Revision 1 created 11/28/2012 by Amara Bot.

1. [Thrun] This very final episode of the computer vision classes
2. I will teach you about structure from motion.
3. This is a really funny name for something much more intuitive,
4. and it comes from the early days of computer vision
5. where the structure referred to the 3D world.
6. And of course it's impossible to capture the 3D world with the camera itself
7. because the camera only gives 2D projections of the 3D scene.
8. Motion referred to the locations of the camera.
9. So the idea was to take a handheld camera and move it around a 3D structure
10. and be able to recover or estimate the 3D coordinates of all the features in the world
11. based on many 2D images.
12. So suppose you have a scene with 3 features--A, B, and C--
13. and you're moving a camera around to different positions--1, 2, and 3.
14. Then the different features get projected onto different points in the camera planes,
15. as shown over here.
16. And from the positions of those projected features
17. it may be impossible to recover not just where the camera was
18. at the time these images were taken but also where in the world the features are.
19. That's called structure from motion.
20. So here is my first quiz.
21. Is this possible?
22. Given that we look at a number of features in the scene--
23. maybe 1, maybe 2, maybe more--
24. and given that we have 1 or more camera positions,
25. can we always, sometimes, or never recover or calculate the 3D position of the features
26. and the 3D position of the cameras simultaneously?
27. Please check almost, sometimes, or never.