As for the reason of design, assembling and the tolerance between cameras, there are zoom (lens focal length inconsistency), tilt(vertical rotation), azimuth(horizontal rotation) differences between the video images, so the physical differences need to be pre-calibrated to get consistent image and easy to get the subsequent images stitching.
In practical applications, the acquisition of panoramic images often requires cameras to be arranged in different positions and different angles of shooting. For example, due to airborne or vehicle characteristics, the camera is arranged in different ways, it can not guarantee that the camera on the same side, such as cylindrical projection is not necessarily in the same cylinder, the plane projection is not necessarily in the same plane; In addition, in order to avoid blinding spots, the camera tends to tilt downward at a certain angle. These conditions are more common, and easy to be ignored, direct projection and then stitching effect is poor. It is necessary to obtain the coordinate transformed images according to the camera's position information and the angle information before all the images are projected onto a cylinder (or plane).
Theoretically, as long as to meet the static three-dimensional image or plane, the corresponding relationship of the two images can be represent by the projection transformation matrix, in other words, as long as any one of these conditions to meet, images taken by a camera can be represented by coordinate transformation as images taken by another virtual camera.