Panoramic detection systems (PDSs) are developmental video monitoring and image-data processing systems that, as their name indicates, acquire panoramic views. More specifically, a PDS acquires images from an approximately cylindrical field of view that surrounds an observation platform. In example of a major class of intended applications, a PDS mounted on top of a motor vehicle could be used to obtain unobstructed views of the surroundings (see Figure 1). In another such example, a PDS could be mounted above a roadway intersection for monitoring approaching and receding vehicles in order to provide image data on the vehicles as input to an automated traffic-control system. In either application, a running archive of the image data acquired by the PDS could be maintained as a means of reconstructing the events leading up to a vehicular collision: used in this way, a PDS would be analogous to an aircraft "black box" data recorder.
The main subsystems and components of a basic PDS are a charge-coupled-device (CCD) video camera and lens, transfer optics, a panoramic imaging optic, a mounting cylinder, and an image-data-processing computer. The panoramic imaging optic is what makes it possible for the single video camera to image the complete cylindrical field of view; in order to image the same scene without the benefit of the panoramic imaging optic, it would be necessary to use multiple conventional video cameras, which have relatively narrow fields of view.
The panoramic imaging optic can be any one of several different types of wide-angle optics. Examples include a panoramic annular lens (PAL), a convex mirror, a fish-eye lens, scanning optics, or a panoramic refracting optic (PRO), which is described in the next paragraph. If necessary, the transfer optics can include one or more mirror(s) to flip the image. Downstream from the panoramic imaging optic and transfer optics, the image is further conditioned by the camera lens, then detected by the CCD in the camera. The camera output is digitized, processed by the computer, and displayed and/or stored as needed.
A PRO is a recently developed optic that operates partly like a PAL, partly like a fisheye lens, and partly like a convex mirror. In comparison with a PAL, a PRO provides a wider field of view, yet is simpler and can be fabricated at lower cost. As shown in Figure 2, light from a scene enters the optic at location 1 (where it is refracted), travels through the optic, is totally internally reflected at location 2, leaves the optic at location 3 (where it undergoes a small amount of refraction), then goes through the transfer optics and camera lens into the camera. The net effect of refraction and reflection from surfaces of the optic is to define the wide, approximately cylindrical field of view. The limits of the field of view are determined primarily by the index of refraction of the optic and the curvature of its refracting/reflecting surface. A significant issue that remains to be addressed in subsequent development efforts is that the resolution of the image is approximately inversely proportional to the angular width of the field of view.