MatLab和Octave函数cp2tform之间的区别

Question

I have a function cp2tform in MatLab. I presume that a function cp2tform in Octave, is supposed to give the same output as the one in MatLab.

The problem is that in some cases the outputs are different.

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Example:

MatLab Code:

A = [1,5; 8,7; 10,15];
B = [0,7; 0,4; 0,5];
cp2tform(A,B,'nonreflective similarity')

Output:

  -0.148848198464265  -0.305965741287655                   0
   0.305965741287655  -0.148848198464265                   0
  -1.810986414648551   8.610750147666863   1.000000000000000

Octave code:

A = [1,5; 8,7; 10,15];
B = [0,7; 0,4; 0,5];
cp2tform(A,B,"nonreflective similarity")

Output:

-0.05960  -0.12252   0.00000
 0.12252  -0.05960   0.00000
-0.72517   6.64570   1.00000

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My question

What am I doing wrong?

Answer 1

That is because you can not describe the transformation between your points using 'nonreflective similarity' .

The correct answer is: both MATLAB and OCTAVE are wrong.

'nonreflective similarity' , from MATLAB:

Use this transformation when shapes in the input image are unchanged, but the image is distorted by some combination of translation, rotation, and scaling. Straight lines remain straight, and parallel lines are still parallel.

But if you look at your points:

There is no way you can convert a triangle into a line with rotation translation and scaling. Therefore, the computation fails.