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Rob Gray, George A. Geri, Shama C. Akhtar, Christine M. Covas; The contribution of 3-D object height and density to altitude maintenance in low-altitude flight. Journal of Vision 2004;4(8):843. doi: 10.1167/4.8.843.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The presence of 3-D objects is known to improve performance in visual simulators, but the relative contribution of various object characteristics is not well defined. We have studied the effects of 3-D object height and density on altitude maintenance in low-altitude flight in an attempt to identify the visual cues that underlie performance on this task. Methods: Six observers attempted to maintain an initial altitude of 30 m during simulated flight over an undulating grey terrain and 3-D objects (trees) of various heights and densities. The tested tree heights and densities were 2.5, 5, 10, and 20 m, and 0.25, 1, 2, 4, and 64 trees/km2, respectively. Flight at 232 m/sec (450 knots) was simulated using a high-performance PC-based image generator (MetaVR Inc.). The visual scene consisted of three, rear-projected, 1600 × 1200 images that together subtended 180° H × 63° V. Results: RMS error in altitude maintenance decreased by a factor of 1.8–2.6 as object density was increased from 0.25 to 64. In addition, the RMS error was strongly related to the product of tree height and tree density (R squared values ranged from 0.74–0.86). Conclusion: On a practical level, there appears to be a trade-off between object height and density in display design (e.g., good flight performance in a low density display can be achieved with taller objects). On a theoretical level, the results suggest that observers estimated altitude using a higher-order visual cue that is a combination of height and density cues.
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