CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

cnng0315 wrote:
> Dear  Loriot : 
>      thanks for your reply,it really helped me a lot.  Before your reply , I
> have been confused for days about this. 
>     I intended to search the tree many times with the same query point, and
> each time I get the result point, I changed its extra info "bUsed", so that
> the next search won't get it. 
>    After reading your reply, I understood the Kd-Tree tree and the
> NN_incremental_search NN are completely diffent things. NN copys the tree,
> so I chaned NN's extra info, but it dosen't change the kd-tree's extra info. 
> I always thouht NN just pointers of tree's point.  Did I get right meaning? 

No, the tree is not copied, a reference to it is kept.
But the value type of iterators is Point_with_transformed_distance
( pair<Point,FT> ) thus the reference on the point you get is an
internal copy of the point.


>  
> Tree::iterator iterS_tree = tree.begin();
>  for (;iterS_tree!=tree.end();++iterS_tree)
>  {
>  std::cout <<iterS_tree->x() <<"," << iterS_tree->y() <<","
> <<iterS_tree->z() <<","<<iterS_tree->bUsed<<std::endl;
>  }
>  
> It seemd there was no way to change tree's point extra info. 
My answer in the previous email was incorrect, the info is indeed not 
modified.

One solution is to use the solution with the property maps I suggested
with a pointer on the points so that the nearest neighbor classes make
copies of the pointers and not of the points (or use integers as in the
example in subsection "Using a Model of L-value Property Map Concept").

Sebastien.

>  
> But it dosen't matter, I changed the code,
>  for (int i=0;i&lt;10;i++)
>  {
>   std::cout&lt;&lt;std::endl;
>   NN_positive_x_iterator
> it(NN.end(),point_not_used(),NN.begin()),end(NN.end(),point_not_used());
>  
> //each time, I get different result with the same query point. 
>   for (int j=0;(j&lt;nK)&amp;&amp;(it!=end);++j,++it)
>   {
>    const Point&amp; p = (*it).first;
>    Point&amp; pp = const_cast&lt;Point&amp;>(p);
>    pp.bUsed = false;
>    std::cout << p.x() <<" "<< p.y() << " " << p.z() <<std::endl;
>   }
>  }
>  
>  
>    oh,thank god and you, it seemd easy, but I just began to use CGAL for a
> few months, it seemd hard for me . anyway, cgal is realy powerful . 
>     Are you familar with CGAL's 3d part, the demos of 3d need Geomview, but
> I have compiled Geomview in windows in Cygwin.  but it failed, always,faild. 
> can you give me some suggestions about how to learn cgal's 3d . Without the
> demos, i don't know what the pdf help says.  I am from China, english and
> math are two big problems for me.  I studied Gis andEngineering Surveying in
> college, and has been do the objectarx (AutoDesk, that's why there were
> errors in my code when you compile it) for years.
>      I found you are skilled with cgal, how many years have you been with
> it?
>
> --
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