Updating point cloud with GeoReference system

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gphysono
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Joined: Fri Oct 06, 2017 1:57 pm

Updating point cloud with GeoReference system

Postby gphysono » Fri Oct 06, 2017 2:20 pm

I’m really new to CloudCompare (and georeferencing n general) so forgive me if this is a simple question.
We have a pointcloud scanned using the cameras local coordinate system. Afterwards we got GPS positions for the area corners and would like to update the pointcloud with that. In other words, switch from the local coordinate system to a Well Known one using the GPS positions as ground points (I think?) I guess that says it all – where/how do you go about that?

P.S. I’m guessing the geoinformation set in CC would carry over into a GeoTiff?

Thanks

daniel
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Re: Updating point cloud with GeoReference system

Postby daniel » Fri Oct 06, 2017 4:30 pm

To geo-reference the point cloud, you have to use the 'Point-pair based alignement' tool: see http://www.cloudcompare.org/doc/wiki/index.php?title=Align.

Instead of using two clouds, you can use this tool with only one cloud and input the reference points (e.g. GPS ones) manually. Another option is to create a cloud with the GCPs and use it as second cloud. You can find messages about this on this forum, but also videos on youtube (simply search for 'cloudcompare georeference' on youtube, there are at least 3 tutorials ;).
Daniel, CloudCompare admin

gphysono
Posts: 4
Joined: Fri Oct 06, 2017 1:57 pm

Re: Updating point cloud with GeoReference system

Postby gphysono » Fri Oct 06, 2017 7:18 pm

Thank you for the fast reply.

The camera is using Meters as it's UOM. The area center is at 0,0 with corners at (-2,-2), (2,-2), (2,2),(-2,2). (approx)
The GPS points are using degrees as it's UOM. The center is at 30.1537585, -85.49869722 with corners at (30.15374152,-85.49872123) (30.15377548, -85.49872123), (30.15374152,-85.49867421),(30.15377548 -85.49867421)

So whenever I do the point pair alignment steps and input the GPS values the cloud gets moved, resized VERY small and still retains it's original camera coordinate system info. What I would like to do is switch the coordinate system to WGS84 since that matches the GPS coordinates I was given.

Can you do that with CC?

Thanks

daniel
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Re: Updating point cloud with GeoReference system

Postby daniel » Mon Oct 09, 2017 6:47 pm

Not sure how you end up with the original coordinate system (you should at least get the GPS one - even though it's in degrees ;). Can't you first convert the degrees to WGS84 one and then use these coordinates for the registration?

As you may have already guessed, CC doesn't handle projections.
Daniel, CloudCompare admin

gphysono
Posts: 4
Joined: Fri Oct 06, 2017 1:57 pm

Re: Updating point cloud with GeoReference system

Postby gphysono » Tue Oct 10, 2017 9:45 pm

Yea I figured that much out lol!
So I ended up taking my las files and exporting them to GeoTiff (Something that I was going to do anyway as part of the workflow...)
Then I learned I could run gdal_translate on them to set the GPS position and projection info.

That leads me to another issue/question, but I'll ask that in it's own thread.

Thanks!


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