Ellipses

Ellipse has a constructor similar to those for Reg_Polygon and Rectangle. The first argument is the center of the Ellipse, and the following two specify the lengths of the horizontal and vertical axes respectively. The Ellipse is first created in the x-z plane, centered about the origin. The horizontal axis lies along the x-axis and the vertical axis lies along the z-axis. The three subsequent arguments specify the amounts of rotation about the x, y, and z-axes respectively and default to 0. Finally, Ellipse is shifted such that its center comes to lie at the Point specified in the first argument.

     Point pt(-1, 1, 1);
     Ellipse e(pt, 3, 6, 90);
     e.draw();
     

Fig. 33.

As you may expect, this constructor has a corresponding setting function:

     Ellipse e;
     real h_save = 1.5;
     real v_save = 2;
     real h = h_save;
     real v = v_save;
     Point p(-1);
     for (int i = 0; i < 5; ++i)
       {
           e.set(p, h, v, 90);
           e.draw();
           h_save += .25;
           v_save += .25;
           h *= sqrt(h_save);
           v *= sqrt(v_save);
           p.shift(0, 0, 2);
       }
     

Fig. 34.