Alignment by Point Picking troubles

[monkeybrainz]

Hello,
I am attempting to use the point picking method for aligning two point clouds, but seem to be missing a step to allow choosing roles for the clouds. How can I chose roles for each cloud to enable point picking?

My steps:
1) load two point clouds. they were taken on a tripod about a meter apart.
2) Merge the frames for each cloud separately. I opted for creating the scalar field for each as well.
3) Select each of the merged clouds using Ctrl+ left click
4) Tools -> Registration -> Align (Point Pairs Picking). I now see the "Entity selector" dialogue. I was expecting to see the "Choose Role" dialogue.
5) "Select All" -> OK
6) Show 'to align' entities is checked. Show 'reference' entities' is grayed out.
unchecking "Show 'to align' entities" hides both point clouds.

I was expecting to see the "Choose Role" dialogue after step 4 as show in this video or documentation


Version
2.11.2, Windows 64 bit.
I was using 2.11.3 before, but uninstalled it after I couldn't get this to work, so I tried this older version.

What am I doing wrong, please?

Thanks for your help,
mb

[daniel]

You shouldn't merge them before aligning them. You have to select 2 separate entities, and then you'll have the choice to select the aligned and the reference one.

Otherwise, CC assumes it's a single entity that needs to be aligned with GCPs (manually input).

[alvaro.lau]

Hello,

I have almost the same issue. I am trying to use the point picking method for aligning two point clouds, but the step "choose the roles" does not show up.

My steps:

a. drag and drop a *.las pointcloud.
b. drag and drop a *.laz pointcloud.
c. ctrl+ left click on both loaded entities (XXX - Cloud)
d. tools - registration - Align (point pair picking)
e. A "Entity selector" popup window appears - select all - Ok
f. a popup window appears with the "show to align entities" checked. Show 'reference' entities' is grayed out. Unchecking "Show 'to align' entities" hides both point clouds.

As the previous comment, I was expecting the "choose role" option, but did not show up.
I followed the same steps as this youtube video.

thanks a lot!
Alvaro.

Version
2.11.3 (Anoia) Windows 64 bit.

[daniel]

So the "choose role" dialog has been replaced by this 'Entity selector' popup window. You should only select one cloud as 'to be aligned' (and not both)

[dylan557]

Hello daniel,

I've just started exploring the points pairs picking feature in cc registration. I'm curious about the algorithm that cc uses to obtain the transformation matrix from three corresponding points. Could you provide some insights into this?

Thank you.

[daniel]

So we use by default the 'Horn' algorithm ('Closed-form solution of absolute orientation using unit quaternions', B.K.P. Horn, 1987).

But for the specific case of 3 points, it's not very reliable (it can flip the solution), so we use a specific approach:
https://github.com/CloudCompare/CCCoreL ... s.cpp#L966

We simply match the centers of gravity of the 2 triplets of points, and then the rotation is the rotation that transforms the normal vector of one set into the normal vector of the other set.