# Rigid Body Structure and Motion From Two-Frame Point-Correspondences Under Perspective Projection

## TL;DR

This paper investigates the feasibility of recovering 3D structure and motion of a rigid body from two frames under perspective projection, concluding that two frames are insufficient due to inherent uncertainty, unlike orthogonal projection.

## Contribution

It demonstrates that, unlike orthogonal projection, perspective projection requires more than two frames for structure and motion recovery, highlighting the limitations imposed by perspective effects.

## Key findings

- Two frames are insufficient for structure and motion recovery under perspective projection.
- Perspective projection introduces uncertainty that prevents recovery from only two frames.
- Orthogonal projection allows recovery from two frames, unlike perspective projection.

## Abstract

This paper is concerned with possibility of recovery of motion and structure parameters from multiframes under perspective projection when only points on a rigid body are traced. Free (unrestricted and uncontrolled) pattern of motion between frames is assumed. The major question is how many points and/or how many frames are necessary for the task. It has been shown in an earlier paper {Klopotek:95b} that for orthogonal projection two frames are insufficient for the task. The paper demonstrates that, under perspective projection, that total uncertainty about relative position of focal point versus projection plane makes the recovery of structure and motion from two frames impossible.