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I have a chessboard in two images with some angle of rotation. Lets find the rotation angle of second image with reference of first image.
For that I found the Rotation Matrix (3x3) and translation matrix (3x1) of those objects.
How can I find the Rotation Angle and Rotation Axis of object using those matrices?
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To find the rotation of a vector we simply multiply the required rotation matrix with the coordinates of the given vector. In 2D space, this is given by ⎡⎢⎣x′y′⎤⎥⎦ [ x ′ y ′ ] = ⎡⎢⎣cosθ−sinθsinθcosθ⎤⎥⎦ [ c o s θ − s i n θ s i n θ c o s θ ] ⎡⎢⎣xy⎤⎥⎦ [ x y ] .
A rotation matrix and a translation matrix can be combined into a single matrix as follows, where the r's in the upper-left 3-by-3 matrix form a rotation and p, q and r form a translation vector. This matrix represents rotations followed by a translation.
cosθ = (r11 + r22 + r33 − 1)/2 . If sinθ = 0, and cosθ = 1 then the rotation vector is r = 0 .
For every type of conversion between rotation representations you have this website euclidean space.
You will find theory and code samples of:
Rotation matrix to quaternion: link
Quaternion to axis angle: link
Rotations in general and all representations: link
And in relation to your question you have Axis Angle. If you have the rotation matrix R (3x3), you can obtain the angle and axis this way (see Matrix to Axis Angle):
angle = acos(( R00 + R11 + R22 - 1)/2);
Axis x,y,x:
x = (R21 - R12)/sqrt((R21 - R12)^2+(R02 - R20)^2+(R10 - R01)^2);
y = (R02 - R20)/sqrt((R21 - R12)^2+(R02 - R20)^2+(R10 - R01)^2);
z = (R10 - R01)/sqrt((R21 - R12)^2+(R02 - R20)^2+(R10 - R01)^2);
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Already working wih openCV I would rcommend using the Rodrigues method: cv::Rodrigues(src, dst, jacobian), that computes the rotation vector if you have a rotation matrix for an argument and vice versa.
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