/* -*-ePiX-*- */
#include "epix.h"
using namespace ePiX;

int main()
{
  picture(P(-1, -1), P(1, 1), "2 x 2in");

  begin();
  /*
  arrow_inset(0.5);
  arrow_ratio(2);
  arrow_width(2);
  */
  double x0(4), y0(0.5), th(Atan(y0/x0));

  P pO(0,0,0), pP(1,0,1), pq(1,0,0), pQ(1,0,-1), pQ1(cis(M_PI/3));
  camera.at(P(x0, y0, 1.25)).range(0);
  bold();

  ellipse(P(0,0,-1), E_1, E_2);
  ellipse(P(0,0, 0), E_1, E_2, -M_PI_2+th, M_PI_2+th);
  ellipse(P(0,0, 1), E_1, E_2);

  line(cyl(1, -M_PI_2+th, -1), cyl(1, -M_PI_2+th, 1));
  line(cyl(1,  M_PI_2+th, -1), cyl(1,  M_PI_2+th, 1));

  line(pQ, pP);
  line(P(0,-1,0), P(0,1,0));
  line(pP, pQ1);
  line(pO, pq);
  line(pO, pQ1);

  dashed();
  ellipse(P(0,0, 0), E_1, E_2, M_PI_2+th, 3*M_PI_2+th, 40);

  label(pP, P(-2,-4), "$P$", bl);
  label(pO, P( 0, 2), "$O$", t);
  label(pq, P(-2,-4), "$q$", bl);
  label(pQ, P( 0,-4), "$Q$", b);
  label(pQ1, P(0,-4), "$Q'$", b);

  tikz_format();
  end();
}