CGAL users discussion list

[Benjamin McWhorter <>]

Hi Sebastian,

I have attached 2 input .OFF files that seem to cause the problem I was 
trying to describe to you.  I have also attached their corresponding .obj 
files.  

If I join the Nef_Polyhedron that I create from these .OFF files, the result 
is not simple.  If I convert it to a polyhedron and then try to print it to 
std output, I get a seg fault.  This is the message that I get from the 
polyhedron builder. 

CGAL::Polyhedron_incremental_builder_3<HDS>::
lookup_hole(): input error: at vertex 1 a closed surface already exists and 
facet 14 is nonetheless adjacent.
             The closed cycle of facets is: 5 1 2.

So I guess my question is, could you maybe help me to understand why the 
result of this join is not simple, or perhaps why CGAL's join does not 
account for this (if those two are different).

However, if I check that the result of the join is valid and simple before I 
join the two, I am able to avoid this problem of not being able to convert my 
results back to Polyhedron, but at the same time it looks like these two 
should be joining together.

Thanks again for all your help.

Ben

Attachment: output4Orig.OFF
Description: Binary data

Attachment: output3Orig.OFF
Description: Binary data

Attachment: Input2.obj
Description: Binary data

Attachment: Input1.obj
Description: Binary data

On Jun 16, 2011, at 2:52 AM, Sebastien Loriot (GeometryFactory) wrote:

> Ben McWhorter wrote:
>> Hi Sebastian,
>> The reason that I test if they are disjoint before joining is because I 
>> need each disjoint nef polyhedron to be output separately.
>> Also, the problem that I was having is that when I would join them 
>> together without the check, I would get resulting nef polyhedron that were 
>> either not simple or not valid.
>> Doing the join the way I do, gives me outputs that are all simple and 
>> valid.  I don't believe that you will have a problem with those 3 examples 
>> I sent in particular, but simply joining all of my input together in the 
>> manner you did gives me a result that is either not simple or not valid.
>> Does that make more sense?
>> If you want me to show you an example of the join producing this invalid 
>> output, I can find some example input that displays the problem.
> Having the input that displays the problem would be nice
> 
> Sebastien.
> 
> [snip]
> 
> 
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