CloudCompare forum

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Hi!

I usually open pointclouds from fixed scanners in CC where each have their origin at the center of the sensor. As expected. But sometimes I run into pointclouds of many scans that have been merged and now they all have one origin (and the sensor data lost ofc)

What I usually do is to chop this pointclouds into smaller chunks, kinda like they were individual pointclouds, using the Sement tool.

But now all the chunks share the same origin as the original merged pointcloud. Is it possible to move the origin for each cloud manually (or maybe can it be moved to it's, lets say, center of gravity?) but still keep the same spacial relation between each other? (ie, to move the origin to moreless the center of the chunk without actually moving the pointcloud?)

I tried creating a sensor which, without any changes to the coordinates, puts the sensor in the same place as the merged origin. And to actually put coordinate numbers in the matrix is way over what my tiny head can achieve.

So I wonder if there's a way to move the origin, or to create this fake sensor in moreless the center of the cloud chunck (after I find its coordinates using the Point Picking tool)?

I really don't see what you will achieve this way, sorry. Do you know the real sensor origins?

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Nope, all the original sensor data was lost when the scans where merged.

And the idea is to have the origin moreless in the center of the pointcloud chunk so it's easier to move it in another software where the movement only happens from the origin. If the origin is outside the pointcloud is harder to move and rotate, less controllable.

Here's an image that hopefully can explain what I want to achieve:



In number 1 there's a merged pointcloud with the origin in its center. Originally it was like around 20 fixed scanner pointclouds, now all merged into one.

In number 2 the merged scan has been chopped in CC in 3 chunks, but each of the chunk's origin is in the same place as before

In number 3 (what I want to achieve) I moved the origin of the chunks to the left and right so now each chunk has the origin in their respective center.

Maybe in CC it doesn't make sense to refer to the "origin of a pointcloud" (not sure) but what I want to achieve is akin to each chunk having their own corresponding sensor in the middle of it.

Thanks for your help!

Indeed, we don't have such a concept (the 'origin' is actually the origin of the coordinate system, and it's purely implicit). You can of course define a sensor object that will have its own origin, but when exporting clouds to most of the standard formats, they don't care about the sensor position at all... (maybe E57, but I'm not even sure we support it in CC at export time ;).

You could take that sensor origin and apply it's inverse transform matrix to the cloud so it would be at the origin prior to saving the individual cloud

daniel wrote: ↑Fri Apr 24, 2020 4:51 pm Indeed, we don't have such a concept (the 'origin' is actually the origin of the coordinate system, and it's purely implicit). You can of course define a sensor object that will have its own origin, but when exporting clouds to most of the standard formats, they don't care about the sensor position at all... (maybe E57, but I'm not even sure we support it in CC at export time ;).

I think CC does support it, I had no problems with moving in this other software pointclouds converted into E57 using CC.

My main problem then is to create a sensor at a specific coordinates, I have no idea how to input the coordinates I got from CC's Point Picking tool into the Create Sensor -> Position + Orientation matrix.

WargodHernandez wrote: ↑Fri Apr 24, 2020 5:34 pm You could take that sensor origin and apply it's inverse transform matrix to the cloud so it would be at the origin prior to saving the individual cloud

Indeed, but I want to retain the current position of the pointcloud chunks, like they were registered. Otherwise they would all collapse and loose their spatial relation between each other.

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Ha, ok, now I get it, C = coordinates and the rest it's just a transformation matrix.

Yet indeed, when saving it as an E57 and opening it back in CC, I dont see the newly created sensor.

But if I edit an E57 that has already a sensor data in it, it is saved. And when I open up this modified E57 the sensor is shown.

Why it's so?

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So, any chance that in the future CC can save the pointcloud with its edited sensor in an E57?

Probably because CC saves this information as 'meta-data' (blindly) and restores it at save time. But it's not able to convert a sensor to the right E57 structure.

And you'll need a motivated developer to make this happen! (as CC mostly relies on its contributors to evolve)

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Ahaaa, now I see.

Well, thanks for taking your time to answer!