Definition
In orthographic projection, light rays are parallel to the axis of the camera, camera and image share the and axes, and the coordinate is dropped: . It completely ignores linear perspective effects.
Scaled orthography
in px/m or px/mm converts metric 3D points to pixels.
With increasing focal length and distance from the camera, a perspective camera behaves more and more like an orthographic one: perspective → weak perspective → orthographic. It is a good model for telecentric and telephoto lenses. Because there is no division by , the mapping is linear, and structure and motion can be estimated together by factorization (SVD).
Appears in
- Lecture 2.1, Projection models
- Lecture 1, History: Tomasi-Kanade factorization for Structure from Motion (1992)