[Scilab-users] mesh2d - finding identical points

Fri Nov 20 12:15:33 CET 2020

In order to use mesh2d with your data, there must exist a plane (u,v) on 
which you could project your (x,y,z) data. The mesh obtained on 
projected data (u,v) would give you the triangulation of the (x,z,y) 
data. This won't be possible with mesh2d if you take for example 
scattered points on a sphere. However, any non-linear transformation 
"unfolding" the data could also help to use pure 2d tools like mesh2d.

S.

Le 20/11/2020 à 12:05, P M a écrit :
>
>
> Am Fr., 20. Nov. 2020 um 11:47 Uhr schrieb Stéphane Mottelet 
> <stephane.mottelet at utc.fr <mailto:stephane.mottelet at utc.fr>>:
>
>     Hi again,
>
>     Le 20/11/2020 à 11:30, P M a écrit :
>>     OK,
>>     some more background:
>>
>>     I actually want to perform a delaunay triangulation on a set of
>>     X-Y-Z-coordinates.
>     I suppose you mean a triangulation of scattered X-Y-Z but you call
>     mesh2d with X-Y only ?
>
>
> Yes, indeed. And there is the bug in my data.
> As x-y coordinates repeat, they do have a different z in the original 
> data.
> But since I call mesh2d with x-y only there are indeed identical points.
>
>>
>>     I know of CGLAB, but it seems only available to Scilab 6.0.x,
>>     while I am on Scilab 6.1.0
>     CGLAB is based on a very old version of CGAL and thus is very
>     hard  to maintain as is. There is a lot of work...
>
>
> I am currently installing Scilab 6.0 to try CGLAB...
>
>>
>>     So the nearest thing to a delaunay triangulation I found is mesh2d...
>     Yeah. Suboptimal choice indeed...
>>     Because of the delaunay triangulation, I am not sure if the order
>>     of points may change.
>     What do you mean ?
>
>
> The scattered points represent a 3D surface geometry.
> If the points will be resorted, I could imagine that the triangulation 
> does not fit to the surface geometry anymore.
>
>>
>>     About unique:
>>
>>     The result I get is actual of same size as the input matrix...I
>>     therefore do assume that each point is unique in the first place
>>     (which they actually should).
>>
>>     What does repeat are individual x, y, z coordinates, but in
>>     different combinations.
>>     So the actual point is different.
>>
>>
>>     e.g.:    x may repeat, but than the y-z-coordinates are different
>>     from point to point
>
>     Could you share the data (you can send me a private message) ?
>
>     S.
>
>>
>>     Thanks,
>>     Philipp
>>
>>
>>
>>     Am Fr., 20. Nov. 2020 um 10:57 Uhr schrieb Stéphane Mottelet
>>     <stephane.mottelet at utc.fr <mailto:stephane.mottelet at utc.fr>>:
>>
>>         Hi Philipp,
>>
>>         Glad to hear that some people use mesh2d. I know we have to
>>         improve the error message by getting the numbers at the
>>         Fortran level... There is also other errors which are not
>>         easy to fix without knowing the number of the problematic
>>         point (point too close to the boundary, for example). Can you
>>         file a bug on BZ ?
>>
>>         S.
>>
>>         Le 20/11/2020 à 10:03, P M a écrit :
>>>         Dear all,
>>>
>>>         using the mesh2d - function I get an error:     mesh2di:
>>>         some points are identical.
>>>
>>>
>>>         How to identify these points and remove the duplicates?
>>>
>>>         There are roughly 500'000 coordinates....
>>>
>>>         Thank you,
>>>         Philipp
>>>
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>>
>>         -- 
>>         Stéphane Mottelet
>>         Ingénieur de recherche
>>         EA 4297 Transformations Intégrées de la Matière Renouvelable
>>         Département Génie des Procédés Industriels
>>         Sorbonne Universités - Université de Technologie de Compiègne
>>         CS 60319, 60203 Compiègne cedex
>>         Tel : +33(0)344234688
>>         http://www.utc.fr/~mottelet  <https://antispam.utc.fr/proxy/2/c3RlcGhhbmUubW90dGVsZXRAdXRjLmZy/antispam.utc.fr/proxy/1/c3RlcGhhbmUubW90dGVsZXRAdXRjLmZy/www.utc.fr/~mottelet>
>>
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>>
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>
>     -- 
>     Stéphane Mottelet
>     Ingénieur de recherche
>     EA 4297 Transformations Intégrées de la Matière Renouvelable
>     Département Génie des Procédés Industriels
>     Sorbonne Universités - Université de Technologie de Compiègne
>     CS 60319, 60203 Compiègne cedex
>     Tel : +33(0)344234688
>     http://www.utc.fr/~mottelet  <https://antispam.utc.fr/proxy/1/c3RlcGhhbmUubW90dGVsZXRAdXRjLmZy/www.utc.fr/~mottelet>
>
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>
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-- 
Stéphane Mottelet
Ingénieur de recherche
EA 4297 Transformations Intégrées de la Matière Renouvelable
Département Génie des Procédés Industriels
Sorbonne Universités - Université de Technologie de Compiègne
CS 60319, 60203 Compiègne cedex
Tel : +33(0)344234688
http://www.utc.fr/~mottelet

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