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# Beginner question: How does a Body relate to Geom?

 Wiki Link: [discussion:17325]
 mvargas Nov 3, 2007 at 4:27 AM I guess a more specific question is: Why does a Body need to be initialized as either a rectangle or a circle; why can't it be an arbitrary polygon? If I want a triangular-shaped object, for example, I understand that I can use GeomFactory.Instance.CreatePolygonGeom() for collision, but how would I initialize the Body representing this object? As a rectangle? As a circle? What does this rectangle or circle represent? All of the samples I've seen have been trivial because the objects in question were already circles or rectangles, but what do I do if I have a triangle or another non-rectangular polygon? DaJackel Nov 3, 2007 at 8:11 AM Now, I'm pretty new to Farseer, but I believe that a body is really nothing more than a point in space with a rotation, it doesn't actually have a shape. The two choices you are giving for a Body, Circle and Rectangle, generate the MOI (Moment of Inertia) based on those shapes. If you would like a more abstract shape, you would have to calculate the MOI yourself, and then just call the non-specific CreateBody() and pass in your custom MOI. I'm no physics expert or Farseer expert, so take this with a grain of salt... mvargas Nov 5, 2007 at 4:45 AM Thanks a lot DaJackel, this sounds like a very reasonable answer. :) I hope that in time we'll see more tutorials / documentation, since Farseer has a lot to offer! crashlander Coordinator Nov 5, 2007 at 4:42 PM There is also now a helper method in the Vertices object, I think, that will return the MOI of a set of vertices. genbox Coordinator Nov 6, 2007 at 8:56 PM crashlander wrote: There is also now a helper method in the Vertices object, I think, that will return the MOI of a set of vertices. Thanks ! I was looking into calculating the MOI of a triangle, Link: http://lab.polygonal.de/2006/08/17/calculating-the-moment-of-inertia-of-a-convex-polygon/ There is a million ways of doing it ! I hope the helper method will help me accomplish this. crashlander Coordinator Nov 7, 2007 at 11:35 AM It should help. And thank BioSlayer... I got the code from him.