Bundle Adjustment——光束平差法

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1. Reprojection Error——重投影误差

Reproject error is a geometric error corresponding to the image distance between a projected point and a measured one. It is used to quantify how closely an estimate of a 3D point X recreates the point's true projection x.

In compute vision domain, reprojection/reconstruction error includes two errors:

feature matching errors;
camera-related errors.

[ https://en.wikipedia.org/wiki/Reprojection_error ]

2. Bundle Adjustment

本质： minimizing reprojection error.

解决两类问题：

adjusting the bundle of rays between:

each camera center(angle of view) and the set of 3D points.
each 3D point and the set of camera centers.

计算基于两个前提：

it requires a good initialization to be provided
it can become an extremely large minimization problem, because of a number of parameters involved.

何时计算此量？

it should generally be used as a final step of any reconstruction algorithm.

[ https://en.wikipedia.org/wiki/Bundle_adjustment ]

[ http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/ZISSERMAN/bundle/bundle.html ]

3. Bundle adjustment ——ray divergence 射线分歧

ray divergence——the shortest distance between those rays.

计算前提：

Assuming accurate feature matching, ray divergence reveals mainly camera parameters estimation inaccuracies.

[Mauricio Hess-Flores, Kenneth I. Joy, et al. Ray Divergence-Based Bundle Adjustment Conditioning for Multi-View Stereo]

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（***）补充内容：

摄像机内外参数（11个--5内6外）：

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5个内参（alpha, beta, x0, y0, theta）和6个外参（R--r1, r2, r3，T--t1, t2, t3）

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常用的相机模型

【David A. Forsyth and Jean Ponce. Computer Vision: A Modern Approach （计算机视觉——一种现代方法）】

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