CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Rational coordinates cannot be represented exactly using a floating 
point representation.

Try to compile this:

#include <iostream>
#include <iomanip>

int main()
{
  std::cout << std::setprecision(18) << 0.7 << std::endl;
}

Sebastien.

On 10/22/2013 03:14 AM, ffmm3 wrote:
> Hello, I am a newer to CGAL, and when I use the .locate() function to locate
> a point in a triangle, there is some problem.
> First I build a triangle with three point (-1,0) (1,0) (0,1),
> Then I check some points' relative location with the triangle,
> the points are:
> p0(0.8, 0.1) ---- locate in the triangle
> p1(0.95, 0) ---- locate on the edge (-1,0) ---- (1,0)
> p2(0.8, 0.2) ---- locate on the edge (1,0) ---- (0,1)
> p3(0.6, 0.4) ---- locate on the edge (1,0) ---- (0,1)
> p4(0.7,0.3) ---- locate on the edge (1,0) ---- (0,1)
> But the locate results are:
> p0 ---- FACE, right!
> p1 ---- EDGE, right!
> p2 ---- OUTSIDE_CONVEX_HULL, wrong!
> p3 ---- EDGE, right!
> p4 ---- FACE, wrong!
> while the points p2, p3, p4 are locating on the same edge (1,0) ---- (0,1)
>
> What's the problem?
>
> The code:
>
> typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
> typedef CGAL::Delaunay_triangulation_2<K>  Delaunay_triangulation;
> void main()
> {
> //generate the triangles
> std::vector<Point2>  pts;
> pts.push_back(Point2(1,0));
> pts.push_back(Point2(-1,0));
> pts.push_back(Point2(0,1));
> Delaunay_triangulation dt;
> dt.insert(pts.begin(), pts.end());
>
> //locate point in the triangle
> Point2 pt0 = Point2(0.8, 0.1);//the point located in the triangle.(on the
> FACE ?)
> Point2 pt1 = Point2(0.95, 0);//the point located on the segment ( (1,0) ----
> (-1,0) ) (on the EDGE ?)
> Point2 pt2 = Point2(0.8, 0.2);//the point locate on the segment ( (1,0) ----
> (0,1) ) (on the EDGE ?)
> Point2 pt3 = Point2(0.6, 0.4);//the point locate on the segment ( (1,0) ----
> (0,1) ) (on the EDGE ?)
> Point2 pt4 = Point2(0.7,0.3);//the point locate on the segment ( (1,0) ----
> (0,1) ) (on the EDGE ?)
> Face_handle fh0, fh1, fh2, fh3, fh4;
> Delaunay_triangulation::Locate_type lt0, lt1, lt2, lt3, lt4;
> int li;
> fh0 = dt.locate(pt0, lt0, li);//for pt0, lt0 is equal to FACE, right!
> fh1 = dt.locate(pt1, lt1, li);//for pt1, lt1 is equal to EDGE, right!
> fh2 = dt.locate(pt2, lt2, li);//for pt2, lt2 is equal to
> OUTSIDE_CONVEX_HULL, I think it's wrong!
> fh3 = dt.locate(pt3, lt3, li);//for pt3, lt3 is equal to EDGE, right!
> fh4 = dt.locate(pt4, lt4, li);//for pt4, lt3 is equal to FACE, I thing it's
> wrong!
> }
>
>
>
> --
> View this message in context: 
> http://cgal-discuss.949826.n4.nabble.com/About-locate-function-tp4658262.html
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