Unroll is splitting my object

Discuss CloudCompare software here.
Post Reply
goodhen
I have made <0 posts
I have made <0 posts
Posts: 3
Joined: Wed Sep 28, 2022 2:58 pm
Full Name: Helen Goodchild
Company Details: University of York
Company Position Title: Project and Fieldwork Officer
Country: United Kingdom
Has thanked: 1 time

Unroll is splitting my object

Post by goodhen »

Hello, I'm new to CC and am just trying to flatten a semi-cyclindrical object. I estimated the radius using a point to point measurement, and used the Auto (gravity centre) option, but for some reason it is pulling my cylinder into two parts, which are also not flat! I've included a couple of views of the project showing the original object and the two-part unrolled object.

If anyone has any tips on what I might be doing wrong that would be really helpful, thank you!
unroll.PNG
unroll2.PNG
You do not have the required permissions to view the files attached to this post.
User avatar
danielgm
V.I.P Member
V.I.P Member
Posts: 183
Joined: Thu Jun 20, 2013 10:45 am
9
Full Name: Daniel Girardeau-Montaut
Company Details: CloudCompare
Company Position Title: Administrator
Country: France
Linkedin Profile: Yes
Location: Grenoble, France
Has thanked: 9 times
Been thanked: 22 times
Contact:

Re: Unroll is splitting my object

Post by danielgm »

Yes, you have to fix the angular range (start angle / stop angle) so that CC can start to 'unroll' the cloud at the right (angular) position.

(and you'll need to use version 2.11 or later)
Daniel
CloudCompare admin
http://www.cloudcompare.org/
User avatar
danielgm
V.I.P Member
V.I.P Member
Posts: 183
Joined: Thu Jun 20, 2013 10:45 am
9
Full Name: Daniel Girardeau-Montaut
Company Details: CloudCompare
Company Position Title: Administrator
Country: France
Linkedin Profile: Yes
Location: Grenoble, France
Has thanked: 9 times
Been thanked: 22 times
Contact:

Re: Unroll is splitting my object

Post by danielgm »

And for the cylinder radius, you should segment the internal cylinder part of the cloud (with the 'scissors' tool). And then use the Ransac Shape Detection plugin to detect/fit a cylinder (ask the plugin to detect cylinders only, and set a high 'minimum number of supporting points' so as to be sure that most of the points are used to fit the cylinder. You'll be able to read the resulting cylinder radius (in the Console or by looking at the fitted cylinder entity properties).
Daniel
CloudCompare admin
http://www.cloudcompare.org/
goodhen
I have made <0 posts
I have made <0 posts
Posts: 3
Joined: Wed Sep 28, 2022 2:58 pm
Full Name: Helen Goodchild
Company Details: University of York
Company Position Title: Project and Fieldwork Officer
Country: United Kingdom
Has thanked: 1 time

Re: Unroll is splitting my object

Post by goodhen »

Brilliant thank you, I wondered if that might be it. Is there a way of finding out where zero (i.e. north azimuth) for determing the angular range is? How does the software decide that? I had tried going from, say, -30 to 270 as an experiment, but it would crash the software every time (even with the new version)

I did try creating a cylinder using the Ransac shape detection, and it created a sort of point cloud, but not a full cylinder, so I couldn't use it. I tried a variety of supporting points, and none worked. At around 10,000 it ran but no cylinder was created (there was a point cloud but no real object), and above 40,000 I just get "segmentation failed". Should I be using more (or less?) points when I sample the surface in the first place? I used about 100,000 originally before I trimmed off the decorative tops and bottoms.

Thanks again.

PS I was using 2.11.3 (Anoia) but have just upgraded to the latest stable version.
unroll3.PNG
You do not have the required permissions to view the files attached to this post.
User avatar
danielgm
V.I.P Member
V.I.P Member
Posts: 183
Joined: Thu Jun 20, 2013 10:45 am
9
Full Name: Daniel Girardeau-Montaut
Company Details: CloudCompare
Company Position Title: Administrator
Country: France
Linkedin Profile: Yes
Location: Grenoble, France
Has thanked: 9 times
Been thanked: 22 times
Contact:

Re: Unroll is splitting my object

Post by danielgm »

The cylinder entity is created but it's not displayed by default. It should be a child of the new output cloud in the DB tree (I believe you just need to expand the DB tree below Cylinder_0001 to see it).

If the revolution axis is 'Z', the zero (azimuth) should be for points aligned with +X (with respect to the cylinder center, if this makes sense :) ). And 90 degrees should be aligned with +Y.

I can't reproduce the crash issue on my side... Would you be able to share a cloud and a snapshot of the parameters you were using? (to admin[at]cloudcompare.org).
Daniel
CloudCompare admin
http://www.cloudcompare.org/
User avatar
danielgm
V.I.P Member
V.I.P Member
Posts: 183
Joined: Thu Jun 20, 2013 10:45 am
9
Full Name: Daniel Girardeau-Montaut
Company Details: CloudCompare
Company Position Title: Administrator
Country: France
Linkedin Profile: Yes
Location: Grenoble, France
Has thanked: 9 times
Been thanked: 22 times
Contact:

Re: Unroll is splitting my object

Post by danielgm »

Here is a visual representation of what I was trying to explain above:
unroll.JPG
You do not have the required permissions to view the files attached to this post.
Daniel
CloudCompare admin
http://www.cloudcompare.org/
goodhen
I have made <0 posts
I have made <0 posts
Posts: 3
Joined: Wed Sep 28, 2022 2:58 pm
Full Name: Helen Goodchild
Company Details: University of York
Company Position Title: Project and Fieldwork Officer
Country: United Kingdom
Has thanked: 1 time

Re: Unroll is splitting my object

Post by goodhen »

I feel very silly I failed to notice the parent/child cylinder, so got that sorted now thank you! I also established the correct range through a bit of trial and error, which ended up being from -270 to 90 degrees. I believe the crash may have been because I wasn't fully understanding how the angles worked and perhaps was inputting invalid ranges.

The curve seems to have been fixed by not using the auto centre of gravity, and taking the centre of the cylinder as the axis position. I realise this is probably obvious to many of you!

Thank you very much for your excellent help!
User avatar
danielgm
V.I.P Member
V.I.P Member
Posts: 183
Joined: Thu Jun 20, 2013 10:45 am
9
Full Name: Daniel Girardeau-Montaut
Company Details: CloudCompare
Company Position Title: Administrator
Country: France
Linkedin Profile: Yes
Location: Grenoble, France
Has thanked: 9 times
Been thanked: 22 times
Contact:

Re: Unroll is splitting my object

Post by danielgm »

You're welcome.

No set of parameters should make the program crash, so don't hesitate to report it if you encounter it again!
Daniel
CloudCompare admin
http://www.cloudcompare.org/
Post Reply

Return to “CloudCompare”