CGAL users discussion list

["Fernando Cacciola" <>]

Hi sinan,

> Hi,
>
> I am reading vertices from a file and then I try to construct a straight
> Skeleton using the polygon
> which is constructed by vertices I read from the file. But in the line "ss =
> ssb.construct_skeleton();" ss becomes "NULL".

The result of "construct_skeleton" is NULL whenever the algorithm failed to 
construct the skeleton.
That can happen if:

1.You are not using a kernel with exact predicates.

2.The input polgon is not simple or has the wrong orientation (CCW for outer 
contours, CW for inner contours)

3.There is a bug,  as the code returns NULL if the generated skeleton is 
detected to be invalid.

HTH

Fernando Cacciola
GeometryFactory