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    <p>Assuming the camera in the video is orbiting the car, here is how you would accomplish that in XNA.</p> <p>For the sake of readability, we'll just use vectors instead of their individual components. So 'target' means it's a Vector3 that includes TargetX, TargetY, &amp; TargetZ. Same with the camera’s position. You can break X, Y, Z values out into fields and make Vector3s out of them to plug into this code if you want to later, but really it would be best for you to work at vector level instead of component level.</p> <pre><code>//To orbit the car (target) cameraPosition = Vector3.Transform(cameraPosition – target, Matrix.CreateRotationY(0.01f)) + target; this.ViewMatrix = Matrix.CreateLookAt(cameraPosition, target, Vector3.Up); </code></pre> <p>Since all matrix rotations act about an axis that intersects the world origin, to use a rotation matrix to rotate the camera around the car, the object of rotation has to be shifted such that the target (and thus the rotation axis) is located at the world origin. CameraPosition - target accomplishes that. Now cameraPosition can be rotated a little bit. Once cameraPosition is rotated a little bit, it needs to be sent back to the scene at hand, that's what the '+ target' at the end of the line is for.</p> <p>The 0.01f can be adjusted to whatever rotation rate suits you.</p>
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    1. COThere are a few minor flaws in this solution: 1) The rotation rate should be multiplied by the elapsed time that frame. 2) I would suggest accumulating the rotation in the angle, rather than the camera position itself - and for good measure I'd probably use `WrapAngle` on the angle.
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      1. USAndrew Russell
    2. CO@Andrew. 1) I agree in practice but I left 'elapsed time' out purposefully to simplify the algorithm so it could be visualized and understood better. Perhaps not a good choice, I don't know. 2) I disagree on this one. It is not good, in 3d, to store angles that have to do with rotations/orientations from frame to frame. In 2d, storing an angular representation of something's orientation is good and proper. In 3d, it's bad. See this link, with an emphasis on the last paragraph on the blog post: http://blogs.msdn.com/b/shawnhar/archive/2010/02/12/doing-math-in-2d-vs-3d.aspx
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    3. CO@Steve I am afraid I disagree. While you are quite right about not using angles for calculations as a general rule, it is perfectly valid to use an angle to place an orbit camera. You have to create a rotation matrix from an angle in order to trace out a circle (you do so yourself). I simply suggest a better way to store it. The thrust of Shawn's article is that an implementation of something like `CreateLookAt` should not use angles and trigonometry - but dot and cross products (which it does).
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