A homography on a real court
One frame of a pickleball final, with the four near-court corners as handles. Modes show the court lines as cross products and their vanishing point, an affine map fixed by three corners against a homography fixed by four, the DLT matrix and its singular values, and the court resampled from above by backward mapping.
Try this
In the homography mode, nudge one corner by 3 px and read the held-out error: centimetres near the camera, and the last line says what one pixel is worth at the far baseline.
Frame 45000 of "2026.07.25 WD Open … (Gold Medal match)" by pickleball4you, CC BY 3.0.
Where this lab comes from
What Is a Homography?How to take a photo of anything flat, a court, a page, a wall, and work out where on it every pixel lies. One pipeline, from painted lines to corners to a 3×3 map to a bird's-eye view, and why a simpler map cannot do it: measured on one frame of a pickleball final, an affine map misses the far sideline by 3.97 m where a homography misses it by 6 cm.
More in cameras and geometry
- Focus, aperture and depth of field — Move the subject and watch the focus plane and the blur follow.
- Four ways a fisheye maps angle to radius — Plot r(θ) for the classical designs against a fitted curve.
- The scene, and what the camera sees — Orbit a 3-D scene on the left; the pinhole view updates on the right.