Hello,
trying to figure out why there is a height difference between laser scans and images when aligned? I am using GCPs
the model is of a street and dips in the middle where the below screenshots are.
Hi, the simple answer is that the data are wrongly aligned.
How many GCPs are you using? Are they placed on both datasets? What is the GCP’s layout? What is the overlap between datasets? Are the data georeferenced? Are you also using some CPs in the places with the biggest difference? What were your alignment settings?
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currently 3 gcps, but can add more to improve the alignment
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yes
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triangle layout e.g. two at either end of the road and one in the middle on the opposite side of the road
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good overlap I assume from the data i have been given
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scans are georeferenced
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Not currently using CPs in these specific areas
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default alignment settings
I suppose three are not enough. But it also depends on the captured area and its size. Also, I would place them on both sides of the road each x meter (depends on the length of the road). Are those GCPs selected from the scanned objects or are they targets?
What camera was used to capture the images? What is its capturing path?
On how many LSPs are those GCPs placed?
Selected from scans, Its about 160 meters camera is sony a7r4 with 14mm lens (not ideal I know)
3 scans with gcps on
If it is 160 m I would use the GCP pair each 10 - 20 m.
By three scans, do you mean the scan positions or created LSPs from RC? As it is different. Can you show 1Ds view with GCPs placing?
Basically it is not sufficient. To make the influence for placed CPs over LSPs they need to be placed on minimally two (ideally more) LSPs. From one placing it is not possible to compute the 3D position of the point.
And with placing GCPs I would go like this:
Also, it seems like GCP point 0 is placed on just few images (maybe three if I see it correctly), which is also just the basic count.
Ok, thanks for the tips and I will try what you suggested.
Just to clarify when you say CP and GCP can you explain what you mean, are you meaning the same thing or different things?
CP is control point, GCP is ground control point and the difference is, that GCP has the coordinates in some coordinate system, where CP doesn’t. It is used to merge the data (could also have the coordinates, but after the computation).
Ok, so is it even necessary to put control points on LSPs
should I just use CPs on images and re align?
Yes, it is also possible.
thanks
But also it depends, how you meant that. Do you want to use the CPs only placed on images and not LSP? If so, it is possible, that the components won’t merge or you will have still the same error. To merge the data correctly place CPs over both datasets correctly.
Right, just wondered if it would make any difference but I will work on it and see if there is an improved result 
This worked, thanks @OndrejTrhan
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