I’m currently studying for an exam (which is in two days) for computer vision but am getting pretty confused with the epipolar geometry stuff. I’m going through some past exam papers and I’m stuck on these two questions. Any help/explanations would be appreciated.
1) How are two cameras placed one with respect to another if epipoles in both the images coincide with the principle points (traces of optical axes)?
2) How are two cameras placed one with respect to another if epipoles in both the images seat infinitely far along the Y-axis of the world co-ordinate frame and have the same x-coordinate?
For the second one, my first guess was the cameras sit on top of one another and face the same direction. I’m not sure if it’s right though.
The epipole is the position of one camera’s centre of projection from the point of view of the other. So:
1) The two cameras are directly facing each other. Think of taking a photo, taking a few steps forwards, turning around 180 degrees and taking another picture. The line joining the centre of projections in the two images is normal to both the image planes.
2) Think of taking a photo, crouching down a few inches and taking another one. If the epipole is at infinity it means that the line joining the centre of projections of the two viewpoints is parallel to the image plane. (The other camera can still be rotated relative to the current viewpoint though)