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[llduncan <>]



plane:  nX=d

line:     mt+p0

 (mt+p0)*n=d

m*nt+p0*n=d

t=(d-p0*n)/(m*n)

 

if(t!=infinity)

   there is a intersection point: m*t+p0

else

   there is no intersection point or have infinity intersection point(平行或重叠)

 

---

llduncan

 

From: Martin Uhrin

Date: 2013-09-27 19:40

To: cgal-discuss

Subject: [cgal-discuss] NaN calculating intersection point of plane and line

Dear CGAL community,

 

I'm having problems calculating the intercept of a plane and a line.

To give one example, the result of an intersection gives me a points

that streams out as:

 

4 5.38925e+2284/9.43119e+2284 0/9.43119e+2284 0/9.43119e+2284 0/1.23183e+2285

 

This is indeed the answer I expect (0.57.. 0 0 0) but represented in

this format I can't get a sensible double out (using to_double),

presumably as it's converting the numerator and denominator to doubles

and then expects to be able to do the division.

 

Background:

 

I'm generating a convex hull with using:

 

typedef CORE::Expr NT;

typedef CGAL::Quotient< NT> RT;

typedef CGAL::Cartesian_d<RT> Kernel;

typedef CGAL::Convex_hull_d< Kernel> Hull;

 

I need a number type that supports quotients and general square roots

and this was the only way (other than using using LEDA which I'd

rather avoid) that I could think of.

 

To get the intercept I use:

 

Kernel::Intersect_d intersect = Kernel().intersect_d_object();

... = intersect(line, hyperplane);

 

where hyperplane is supporting a facet of my hull.

 

Any ideas on how I can get a sensible double out would be much appreciated.

 

Kind regards,

-Martin

 

-- 

Martin Uhrin                                                  Tel: +44

207 679 3466

Department of Physics & Astronomy               Fax:+44 207 679 0595

University College London                         

Gower St, London, WC1E 6BT, U.K.         http://www.cmmp.ucl.ac.uk

 

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