CGAL users discussion list

[Mariette Yvinec <>]

Alpha_shape_3 has an output operator to a Geomview_stream
that will let you see the boundary facets with Geomview.
If you don't have Geomview at hand you can  look at the code in
CGAL/IO/alpha_shape_geomview_ostream_3.h
and write similar code for another viewer.

Hope this helps.
Mariette

Andi Jochem wrote:

But how can I write the boundaries into a file. I would like to have look on the boundaries to be able to decide which is the best alpha for my set of points.

andi
-------- Original-Nachricht --------
  

Datum: Fri, 08 Aug 2008 15:41:45 +0200
Von: Mariette Yvinec 
An: 
Betreff: Re: [cgal-discuss] Boundary of alphashapes
    

Depending on the value you are going to choose for alpha,
you can get a whole family of different alphashapes
with different boundaries.

I am not sure that one of them corresponds to
what you are expecting

 wrote:
    

Hello Mariette,
you are right, there is no relation between alphashapes and shapefiles.

The only thing I want to do, is to write the boundaries which are
      

defined by the set of points into a file.
    

Or am I totally wrong and alphashapes are not the right method to solve
      

my problem.
    

Thanks 

andi


-------- Original-Nachricht --------
  
      

Datum: Fri, 08 Aug 2008 14:59:14 +0200
Von: Mariette Yvinec 
An: 
Betreff: Re: [cgal-discuss] Boundary of alphashapes
    
        

 From what I see in wikipedia
there is no relationship between alphashapes and shape file...

and I still don't get what shape you want to get

Andi Jochem wrote:
    
        

Hello Mariette,

a shapefile is a popular geospatial vector data format for geographic
      
          

information systems
    
        

(http://en.wikipedia.org/wiki/Shapefile)

As you already know, I am not very familiar with alphashapes, but
          

maybe
    

you can help me.
    
        

I am just looking for a method to get the shape, defined by a set of
      
          

points (the "concave hull" , not the convex hull). After an intensiv
        

google
    

search, I found the CGAL library, installed it and tried to write a
        

function
    

using alpha_shapes_3.
    
        

My question is: How can I get, the shape which is defined by a set of
      
          

points in file?
    
        

 

Thanks

Andi




-------- Original-Nachricht --------
  
      
          

Datum: Fri, 08 Aug 2008 14:37:54 +0200
Von: Mariette Yvinec 
An: 
Betreff: Re: [cgal-discuss] Boundary of alphashapes
    
        
            

I am rather familiar with Alpha_shape_3
but I  can't answer your questions
because I do not  understand them...
In particular I don't know
- what is a shapefile
- nor which polygon you want to get out of alpha_shapes_3
- nor what is  a roof plane

 wrote:
    
        
            

Hello,
I wrote a function to get the alphashapes of a set of points, but
              

how
    

can I
    
        
            

transform this alphashapes in a polygon...???
Is it posssible to transform the created alphashape in a
              

shapefile???
    

Is anybody familiar with alphashapes?? 

Thanks a lot.

andi
  
      
          
              

-- 
Mariette Yvinec
Geometrica project team
INRIA  Sophia-Antipolis  



-- 
You are currently subscribed to cgal-discuss.
To unsubscribe or access the archives, go to
https://lists-sop.inria.fr/wws/info/cgal-discuss
    
        
            

-- 
Mariette Yvinec
Geometrica project team
INRIA  Sophia-Antipolis  



-- 
You are currently subscribed to cgal-discuss.
To unsubscribe or access the archives, go to
https://lists-sop.inria.fr/wws/info/cgal-discuss
    
        

-- 
Mariette Yvinec
Geometrica project team
INRIA  Sophia-Antipolis  



-- 
You are currently subscribed to cgal-discuss.
To unsubscribe or access the archives, go to
https://lists-sop.inria.fr/wws/info/cgal-discuss
    

-- 
Mariette Yvinec
Geometrica project team
INRIA  Sophia-Antipolis