title: Finding Contact point - Box2d with Cocos2d
body: <p>I'm building a game with Cocos2d + Box2d</p>
  
  <p>I want my hero's jump direction to be
  orthogonal to the ground he is standing on.</p>
  
  <p>My idea is that I use a vector from the contact point
  (hero with ground) to the Center of the Hero Sprite.
  Then I use an impulse to make the hero jump.</p>
  
  <p>Has anyone an idea how I could do this?
  How can I find out the contact point?</p>