cloud registration without scale adjustment

[kayem12]

Hello,

What happens to the global shift of a cloud if it is finely registered to another reference cloud with the "adjust scale" button left unchecked?

[HeadLess]

If you register something to something else, then everything will be in the same pos/scale as the something else. So the toAlign cloud(s) will be transformed to the reference cloud.

If the reference cloud has global shift every to align cloud will have the same global shift.

[daniel]

The 'adjust scale' button is just to allow the global scale of the to be aligned cloud to be modified so as to better match the reference entity.

If you don't enable this option, then you'll have a truly 'rigid' transformation of the to be aligned cloud, without any modification of the scale (that should be the default option, especially if you work with data for which you trust the scale, such as a good scanner, etc.)

[kayem12]

Thanks Daniel and Headless.

I am still trying to understand the fine registration tool.

This is an image I aligned with the rotate and translation tool, green being the image I am aligning and the RGB layer the reference image

eg3211.png (1.96 MiB) Viewed 3073 times

when I went and did a fine registration without scale adjust, it placed the layer to aligned in a wrong position

3212-fineregistration.png (1.39 MiB) Viewed 3073 times

and when I chose fine registration with scale adjust, it shrank the image to be aligned (seen peeking out at the edges of the reference RGB image)

321-fineregistrationwscaleadjust.png (1.19 MiB) Viewed 3073 times

.

The images I am aligning are lidar from UAV flights with problematic real time kinematic data.

I really appreciate you sharing your knowledge and am still learning CC and how powerful a tool it is.

[HeadLess]

Well i'm not really using cloud compare for registration but when i do then i usually only use the align tool. So i pick my own points then align. Especially in your situation when there is no really good features. It is probably better if you can find few matching points dotted around the cloud.

https://www.cloudcompare.org/doc/wiki/index.php/Align

[daniel]

Have you set the overlap parameter correctly? Because from the image of the starting position, it seems the overlap is very small. You should set this parameter accordingly (otherwise will algorithm will try to make all the points of the 'to be aligned' cloud as close as possible to some points of the reference cloud.