Incorrect orientation of point cloud

[juliana]

Dear CloudCompare community!

I'm currently working on my Master's thesis with TLS-data and I need some advice.
We have point cloud from the handheld scanner (research area in the forest) and measured positions of reference targets/objects. We need transform point cloud to reference coordinate system (JTSK) according to the position of the reference objects and the corresponding ones (with known local coordinates), so we decided to use the Align (point pairs picking) tool. I picked 6 pairs of equivalent points in our clouds. I filled out the coordinates manually.
The problem is, that after transformation, Z-axis is conversely rotated, so on the ground the high of the point cloud IS above the sea level - around 410 meters and in the canopy around 395meters.
And I can't edit the transformation matrix, because I need the right rotation of the cloud with respect to the axis immediately after the first transformation.

Thanks in advance

Juliana

[daniel]

Several things can happen here:
- you made a mistake in the pairing of real and manual points (but if you take 6 pairs, it's unlikely it's just a simple mistake)
- your global coordinates are not in a 'direct' coordinate system, or the cloud is not (e.g. mirrored, etc.)
- you took all the reference points on a plane and you fall in one of the few degenerate configuration that can cause this flipping (once again, very unlikely if it's 6 pairs with real life reference points).

Can you maybe share with me the cloud and the reference points so that I can take a look on my side? (admin [at] cloudcompare.org)

[juliana]

Hi, Thank you for replying.
The problem is that our reference coordinate system is located in the third quadrant (compared to other systems) which normally contains negative values, so I edited all reference values to negative form and it works.
Thank you