CGAL users discussion list

[Simon Giraudot <>]

Hello,

What do you mean by filters? If you're talking about functions of CGAL 
Point Set Processing (for example CGAL::grid_simplify_point_set()), some 
of them reorder the input range, which means you loose the original 
indices. That could explain why you're experiencing problems if you rely 
on the original order.

There's a way to avoid altering the point set order using dedicated 
property maps: the principle is that you create a range of indices 
(trivial, just the ordered indices from 0 to N-1, N being your number of 
points), and use a property map referencing the original range to 
recover the right point/normal. That way, the functions that reorder the 
input range will just reorder the range of indices and leave your 
original point range unaltered (then you can just use the range of 
indices to access the elements you want). You can see an example that 
does that in Spatial Searching: 
https://doc.cgal.org/latest/Spatial_searching/index.html#title12

It may seem a bit tricky but in practice it's very handy.

I hope this helps :)

--
Simon Giraudot, PhD
R&D Engineer
GeometryFactory - http://geometryfactory.com/

Le 01/07/2019 à 15:21, cisant a écrit :
> Oh God!! Thanks for the answer!! It works very well if I don't use any
> filter. But, if I execute some filter on my point set after read the file
> with the XYZ coordinates, I can't write the color correctly.
>
> How could I know the index of a point in order to compare with the archive
> that my program already read? Maybe searching by the index, I'll be able to
> write the right color for the point.
>
>
>
> --
> Sent from: http://cgal-discuss.949826.n4.nabble.com/