One point, one line in the other view
Every 3-D point along one pixel's ray lands on a single line in the second image. Depth markers sit on that line, which makes the core idea tactile: matching along the epipolar line is choosing a depth.
Try this
Shrink the baseline toward zero. The line degenerates and depth stops being observable — the same failure a stereo rig has when its cameras are too close together.
Where this lab comes from
Structure from Motion, from Scratch: 47 Photos to a 3-D Temple in ~800 Lines of PythonHow overlapping 2-D photos become 3-D points and camera poses: SIFT matching, the essential matrix, triangulation, PnP growth, and sparse bundle adjustment, built from scratch with OpenCV + SciPy. The pipeline registers all 47 Middlebury temple views at 0.25 px mean reprojection error, next to COLMAP's 0.30 px on the same images. Worked examples, three interactive labs, and the reconstruction growing image by image.
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.