* get a ray (2 points) from a pick point in GL area
* @param x mouse position
* @param y mouse position
* @param rayA first computed point of ray
* @param rayA second computed point of ray
* @param radius radius on pixel for clicking precision
* @return the distance in modelview world corresponding to radius pixel in screen
*/
// GLfloat getOrthoScreenRay(int x, int y, Geom::Vec3f& rayA, Geom::Vec3f& rayB, int radius=4) { return m_glWidget->getOrthoScreenRay(x,y,rayA,rayB,radius);}
/**
* transform a pixel distance on screen in distance in world
* @param pixel_width width on pixel on screen
* @param center reference point on world to use (defaut 0,0,0)