07-03-2026, 05:04 PM
Visual geometry of a sphere
BY [Stijn Oomes]
Summary
The article explores how we perceive the size of spherical objects in photographs and how geometry can be used to recover their real-world dimensions from a 2D image. Using a simple but clever setup—several spheres placed on a flat surface with an A4 sheet as a reference—the author shows how knowing the camera’s position and some measurable image features allows one to mathematically estimate the true radius of each sphere.
The key idea is that a sphere projects into an ellipse-like shape depending on the viewing angle, and by modeling this projection with tools from projective geometry, one can extract accurate 3D information from a single photo. The author highlights that this approach can achieve surprisingly precise results, often outperforming human intuition about object size, and suggests practical uses in areas like vision systems and motion tracking. Overall, it’s a neat blend of math, geometry, and real-world imaging intuition.
BY [Stijn Oomes]
Summary
The article explores how we perceive the size of spherical objects in photographs and how geometry can be used to recover their real-world dimensions from a 2D image. Using a simple but clever setup—several spheres placed on a flat surface with an A4 sheet as a reference—the author shows how knowing the camera’s position and some measurable image features allows one to mathematically estimate the true radius of each sphere.
The key idea is that a sphere projects into an ellipse-like shape depending on the viewing angle, and by modeling this projection with tools from projective geometry, one can extract accurate 3D information from a single photo. The author highlights that this approach can achieve surprisingly precise results, often outperforming human intuition about object size, and suggests practical uses in areas like vision systems and motion tracking. Overall, it’s a neat blend of math, geometry, and real-world imaging intuition.
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│ KONSTANTINOS MICHAILIDIS │
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│ KONSTANTINOS MICHAILIDIS │
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