Adding Transformation Matrices...???

[civengrgmu]

I'm working through the registration of two point clouds. I follow the traditional method when working in CloudCompare where I do the manual alignment through point-pair selection, which gives me the first transformation matrix. Then, I use the fine registration, which gives me the second transformation matrix.

If I wanted to apply a single transformation matrix to the original "Compared" point cloud (in its position prior to the manual point-pair selection) to get it into its final registered position, could I add the two transformation matrices that I originally found to each other (while keeping the last row as [0 0 0 1])? I know that this works for tx, ty, tz, but I'm not sure about the rotations...

The reason that I am asking this is because I am looking at a "sensitivity study" based on locations selected for the manual point-pair selection. Instead of saving a whole bunch of point clouds, I'd prefer to just save the transformation matrices due to storage concerns (I'm working with large point clouds). When going back through my results, it would be nice to be able to apply just one transformation matrix per scenario to get back to the final registration.

Thanks.

[civengrgmu]

Well, I just answered my own question (I hate it when I do that... but not really). It turns out you only need to do matrix multiplication of the [fine registration transformation]*[point-pair picking transformation]. If you want an explanation, this website has a good one: https://www.brainvoyager.com/bv/doc/Use ... rices.html

[daniel]

Ah ah yes, you got it right.