CGAL users discussion list

[Cristiano Nattero <>]

Hello everybody,

   I'm experimenting with rotations of a 2D polygon and something
strange happens: it looks like I could rotate it CW but not CCW!

I can't spot the problem :(

Here's the code:

//------------------------------------------------------------------------------------

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Vector_2<K> Vector;
typedef CGAL::Aff_transformation_2<K>  Transformation;
typedef CGAL::Polygon_2<K> Polygon;

//[...]


Polygon transformPolygon( const Polygon& P, const Vector& v, const
long double& angle )
{
        Transformation t( CGAL::TRANSLATION, v );
        Transformation r( cos( angle ), -sin( angle ), 0, sin( angle ), cos(
angle ), 0, 1 );
        Polygon tempP;

        tempP = transform( t, P );
        tempP = transform( r, tempP );

        return tempP;
}

//[...]

Vector v( 1, 0 );

long double angle;

//------------------------------------------------------------------------------------

v is initialized as shown above.

When I call the function with

angle = - M_PI / 2;

it works fine. It doesn't when

angle = M_PI / 2;

Where's the error?

Thank you very much for your help :-)

-- 
Ciao,
Cristiano Nattero