SLAM 내가 모르는 keyword 정리

SLAM(Simultaneous Localization And Mapping)

- Odometry + Loop closure



stereo 이점: estimate the exact trajectory 



monocular 이점: only estimate the trajectory, unique only up to a scale factor.



http://avisingh599.github.io/vision/visual-odometry-full/



Undistortion: lens distortion을 보완, calibration과정에서 얻는 distortion parameter로 수행됨



Rectification: disparit map 연산의 문제점을 줄이기 위해 수행. 모든 epipolar line들이 parallel -> horizontal로. disparty computation에서 matching blocks를 한 방향으로만 찾으면 됨

# Disparity Map Computation

스테레오 카메라를 통해 나온 pair images를 통해 disparity map을 계산할 수 있음

첫 이미지의 (x,y)가 두 번째ㅐ 이미지의 (x+d, y)에 존재한다면 좌표 (x, y)의 disparity map에는 value d를 갖고있다.

 y좌표는 동일(rectified됐기 때문). 즉, d = x(first) - x(second)



# Block-Matching Algorithm

sliding window를 사용해 각 좌표의 disparity를 계산. 



# Sum-of-Absolute Differences(SAD 알고리즘)

https://blog.naver.com/ppgt1225/100191849023

https://studyandroid.tistory.com/66

http://zone.ni.com/reference/en-XX/help/372916M-01/nivisionconceptsdita/guid-53310181-e4af-4093-bba1-f80b8c5da2f4/

영역의 유사성을 측정하는 알고리즘



# Feature Detection

- FAST: http://www.edwardrosten.com/work/fast.html

https://m.blog.naver.com/PostView.nhn?blogId=samsjang&logNo=220655420471&proxyReferer=https%3A%2F%2Fwww.google.com%2F





focal length - pinhole과 film(image plane) 사이의 거리



visual odometry



egomotion



calibration - 우리가 보는 세상은 3차원, 카메라로 찍을 경우 2차원 이미지가 됨. 이 때 3차원의 점들이 어디에 맺히는지는 당시의 카메라의 위치/방향에 의해 결정. 하지만 실제 이미지는 사용된 렌즈, 렌즈와 이미지 센서와의 거리, 각 등 카메라 내부의 기구적인 부분에 의해서 큰 영향을 받음. 따라서 3차원 점들이 영상에 투영된 위치를 구하거나 역으로 영상좌표로부터 3차원 공간좌표를 복원할 때에는 이러한 내부 요인을 제거해야만 정확한 계산 가능, 그리고 이러한 내부 요인의 파라미터 값을 구하는 과정이 calibration(https://darkpgmr.tistory.com/32?category=460965)



extrinsic parameter: 카메라 외부 파라미터(카메라의 설치 높이, 방향(팬, 틸트) 등 카메라와 외부 공간과의 기하하적 관계에 관련된 파라미터



intrinsic parameter: 카메라 내부 파라미터(카메라 초점거리, aspect ratio, 중심점 등 카메라 자체의 내부적인 파라미터)

https://darkpgmr.tistory.com/32



SFM(Structure from Motion)



bundle adjustment



degree of freedom(DOF)



Moravec -> 1. motion estimation pipeline, 2. corner detector(Moravec corner detector)

  - slider stereo 를 사용(a single camera sliding on a rail) - stop and go fashion, digitizing and analyzing images at every location



epipolar line: https://darkpgmr.tistory.com/83