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This research investigated the effect of providing three different simulations of ground terrain on the ability of subjects to accurately determine the aimpoint during a final approach. Several simulations were created to model a straight-in final approach (3 degree glideslope) to a standard FAA runway from several distances. The three levels of terrain realism ranged from a homogeneous surface to farmlands with hills. The subject's task was to estimate the aimpoint which represented an extrapolation of the flightpath to its point-of-contact with the ground as well as the altitude at nine different distances from threshold. The results indicated that increased levels of realism lead to better performance in judging altitude and predicting aimpoint during a simulated final approach.

SUMMARYThis contractual effort studied a prioritized list of psychophysical aspects of visual simulation systems for military flight training simulators. The available literature, operational experiences of simulator commands and current research program data were assembled, organized, reviewed, evaluated, and summarized to provide psychophysical criteria for the visual displays subsystem. Through this process, some areas of insufficient data were identified, and a selection of those that were amenable to psychophysical investigation was recommended, with suggested experimental designs.The prioritization of 41 system characteristics as to their relative importance was a product of rank ordering and applying weights assigned to five evaluation factors. The factors were false cues, interaction of characteristics, current prevalence, realism deficiency, and cost of correction. The following characteristics are those discussed in detail within this report. ALIASING DefinedIn its restricted sense, aliasing refers to the presence of harmonics in the signal leading to an unintended distortion in the information displayed on the cathode-ray tube (CRT). The more current usage of the term aliasing refers to a number of visual anomalies, e.g., shearing, racing, edge walking, angular velocity dependent resolution. Potential EffectsThe possible effects of aliasing include the following: (a) imposes smoothing requirements that reduce display resolution, (b) allows incidental learned effects that are not useful in real flight, (c) provides distractions that use up available time thereby adding to the pilot's work load, (d) imposes changes of visual search patterns, and (e) decreases pilot acceptance of visual simulation. Method of MinimizationThe general solution is to minimize effect by "smoothing" of edge gradient by software routines, using 60 Hz update and refresh rates, and using lower contrasts 1n the scene. One promising anti-aliasing technique Lhat is a feasible alternative to pre-filtering is to oversample the data, apply a digital low-pass filter, and then down-sample the data to the resolution of the display. _..i MAGNIFICATION DefinedThree types of magnification are related to perceptual effects in a visual simulation system. These are (a) uniform magnification within the optical system with image size which subtends the correct visual angle for the object size and distance portrayed, (b) uniform magnification of a scene to an image size (visual angle subtense) larger than that dictated by the size-distance relationship, (c) non-uniform magnification, in which objects in some areas of a display are magnified more than objects in other areas. Potential EffectsFor type (b), the danger is in a "flattening" effect produced by the differential ratio of magnification of near and far objects, causing misperception of distance and approach angle relative to the terrain surface. Type (c), uneven magnification will produce distortions, and uneven relative magnification of the images presented to each eye will impose general ...