CGAL users discussion list

[Andreas Fabri <>]

Hello,

You might have a look at the tutorial that is already in the documentation
of the master branch

https://cgal.geometryfactory.com/CGAL/doc/master/Manual/tuto_reconstruction.html

With Poisson you will not have your input points as mesh vertices.

The documentation states that Poisson produces a water tight surface.
This is apparently a simplification (or a bug), because you obtain
a mesh with borders, but a planar data set is not well suited
for Poisson. 

Best,

Andreas

On 9/8/2020 7:41 AM, sindhu r ( via cgal-discuss Mailing List) wrote:

Hi Sebastien,

Thanks for the reply and the link. I was under the impression that I was following one of the suggested pipelines in the manual for my overall task (read point cloud as xyz, compute and orient normals as xyz, perform poisson reconstruction into .off, transform into mesh, use with surface mesh shortest path package).

You're right, I am providing a grid of points as the simplest test case of a point cloud to see where I'm going wrong. I am assuming that when that surface is reconstructed, it should look like a 6x6 grid. My confusion is that the surface does not look like a grid at all- even before I remove isolated vertices it looks like a dagger and some vertices have coordinates that exceed the range specified in my point cloud. I am unsure of where I'm making a mistake.

Anyway, thanks for your help, I'm probably making a silly mistake somewhere.

Sindhu R

On Tue, Sep 8, 2020, 1:00 AM "Sebastien Loriot (GeometryFactory)" <> wrote:

Your input point cloud is basically a grid of points in a plane.
I don't know what you expect as output but poisson reconstruction
algorithm is probably not the right tool for that task (Advancing front
seems more appropriate to me).

You should read the new tutorial written by Simon Giraudot about
reconstruction available here:

https://cgal.geometryfactory.com/CGAL/doc/master/Manual/tuto_reconstruction.html

Best regards,

Sebastien.

On 9/7/20 8:28 PM, sindhu r ( via cgal-discuss
Mailing List) wrote:
> Hello,
> I am trying to do the following:
>
>  1. define a set of 3d coordinates describing a surface
>  2. compute and orient normals
>  3. generate a polyhedral mesh and save it to a .off file for further use.
>
> What I have done so far: I have accomplished all 3, however my
> polyhedral mesh and my .off file seem incorrect.
>
> My .off file (attached) was generated using the points and normals from
> a .xyz file (also attached). The xyz file represents points that span
> the x-y plane 0 <= (x,y) <= 6, and 0 <= rand(z) <= 0.2. It does not have
> any holes or islands; it looks like a blanket. My final test case will
> involve holes and/or islands, but for the moment even this simple
> example shows something strange about the .off file that I generate
> using the Poisson reconstruction method.
>
> While the .xyz file contains points respecting the 0 <= (x,y) <= 6, and
> 0 <= rand(z) <= 0.2 condition, my .off file seems (lines 4, 7, 8 etc..)
> to have vertices with x,y,z locations that are way off my points
> specified in the .xyz file. I think I'm using the Poisson reconstruction
> incorrectly (minimal working code attached). The image of the polyhedral
> mesh (attached) does not remotely resemble what I hoped for :(.
>
> I'm sorry if it is a basic question, and I would be grateful for any
> guidance. Thank you!
>
> Regards,
> Sindhu R
>
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Andreas Fabri, PhD
Chief Officer, GeometryFactory
Editor, The CGAL Project

phone: +33.492.954.912    skype: andreas.fabri