It can be proven that the perspective projection (or camera projection) of a circle is an ellipse. But I also need to prove that the semi-major axis has the same size as the radius of the original circle. Any idea on how to prove it? Cheers!
2026-04-01 13:00:41.1775048441
Perspective projection of a circle: what is the size of the semi-major axis?
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If I take a photo of the circular cross section of the moon using my 35mm camera, then the resulting image on my 35mm film is certainly smaller than the moon itself, along any axis. Nevertheless, this transformation from plane in the world world to plane of the film would usually be considered a perspective transformation. So unless you have a more restricted definition of a projective transformation than what is usually used, your assumption is incorrect.