Computer Image Generation System With Efficient Image Storage

IntroductionVisual display systems for training simulators have traditionally used large modelboards for scene image storage. The inherent physical nature of model boards makes theman inefficient method of image storage. In addition, other physical problems severely limitthe range of training scenarios(1).The revolutionary field of computer image generation (CIG) avoids these physical problemsby storing scene image data in a mathematical form in computer memory. Real time generationof perspective views of the scene, however, requires such high computation rates that thecurrent state of the art in CIG is limited to using the simplest image primitives, straightedges bounding planar patches. The modeling of curved surfaces is therefore crude and in-efficient. Many edges are required resulting in a large, clumsy data base. In addition, theresulting image is quite stylized and cartoonish. In order to provide a more compact andefficient scene storage data base and produce a more realistic image, the Grumman AerospaceCorp. has developed a Modified Ray Tracing Method for generating images of curves surfaces.The Modified Ray Tracing MethodThe Modified Ray Tracing Method stores a three -dimensional scene in computer memoryas follows. The scene is composed as a set of objects, each of which is defined by thevolume bounded by a few first- and second -order surfaces. For example, a wing can bedefined by a thin elliptical cone bounded by two planes (Figure 1). Using a number of suchobjects we can compose a scene of a KC -135 refueling tanker (Figure 2). In order to pro-ject a perspective view of the scene we separate the scene information into two parts.The high -order information, shown in the left part of Figure 2, consists of those imagepoints where scene information changes rapidly from picture element to picture element.These points include only a small fraction of the total number of image points and arecalculated precisely. The low -order information, shown in the right part of Figure 2,consists of those image points where scene information changes slowly. These points includemost of the image points and are calculated approximately.In addition to the added realism provided by the use of true curved surfaces anincrease in image storage efficiency is produced. Figure 2 shows a comparison between theModified Ray Tracing Method data base and that required using standard edge methods todescribe the same scene. A savings of 10 to 1 in computer storage is achieved.TexturingIn order to model natural features such as mountainous terrain we use curved surfaceswith texturing overlaid. Figure 3 shows how four hyperboloids can be used to model amountain range. Texturing, composed of six sine waves, is overlaid to give a more naturalappearance. The entire scene requires storage of only 190 data values, 178 for the sur-faces and 12 for the texturing.SummarLThe Modified Ray Tracing Method provides a means of efficient scene image storagefor simulator displays. A savings of 10 to 1 over standard CIG data bases is achieved.In addition, the use of curved surfaces and texturing provides more realism in the gener-ated images.References