How does align tool work ?

[Jean-Yves]

Hello,
I'm looking for documentation to understand how the “align” tool works.
On which values is the root mean square calculated?
How does it work?

Thank you in advance.

[daniel]

So the documentation is here: https://www.cloudcompare.org/doc/wiki/index.php/Align

And the RMS is simply the root of the average squared distance between every pair of points (after registration).

[Jean-Yves]

Thank you very much.

If I understand correctly, this is a 7-parameters HELMERT transformation such that the distance between each pair of points is minimised ?

[daniel]

Yes, I believe we use Umeyama's algorithm to find it.

And before we were using: 'Closed-form solution of absolute orientation using unit quaternions', B.K.P. Horn, 1987.