Prevalence of the terrain reversal effect in satellite imagery

The terrain reversal effect is a perceptual phenomenon which causes an illusion in various 3D geographic visualizations where landforms appear inverted,e.g.we perceive valleys as ridges and vice versa.Given that such displays are important for spatio-visual analysis,this illusion can lead to critical mistakes in interpreting the terrain.However,it is currently undocumented how commonly this effect is experienced.In this paper,we study the prevalence of the terrain reversal effect in satellite imagery through a two-stage online user experiment.The experiment was conducted with the participation of a diverse and relatively large population(n=535).Participants were asked to identify landforms(valley or ridge?)or judge a 3D spatial relationship(is A higher than B?).When the images were rotated by 180°,the results were reversed.In a control task with‘illusion-free’original images,people were successful in identifying landforms,yet a very strong illusion occurred when these images were rotated 180°.Our findings demonstrate that the illusion is acutely present;thus,we need a better understanding of the problem and its solutions.Additionally,the results caution us that in an interactive environment where people can rotate the display,we might be introducing a severe perceptual problem.

Comparing the terrain reversal effect in satellite images and in shaded relief maps:an examination of the effects of color and texture on 3D shape perception from shading

Terrain reversal effect(TRE)causes reversed 3D shape perception in satellite images and shaded relief maps(SRMs),and introduces difficulties in identifying landforms such as valleys and ridges.With this paper,in a controlled laboratory experiment,we compare how well 27 participants could identify valleys and ridges over 33 locations using SRMs,color satellite images and grayscale satellite images.The main depth cue is shadow both in vertical-view images and SRMs.However,the presence of texture and color in images also affect 3D shape perception.All our participants experience the illusion strongly:with the SRMs,it is very severe(2%accuracy),with grayscale images low but considerably better than SRMs(17.6%accuracy),and slightly worse with color imagery(15.3%accuracy).These differences between SRMs and imagery suggest that the participants who are able to bypass the illusion consciously or subconsciously interpret the photographic information.We support this observation further with a cue-strength analysis.Furthermore,we provide exploratory analyses of the effects of expertise,global convexity bias,and bistable perception.Our original empirical observations serve towards a better understanding of this visual illusion,and contribute towards nuanced and appropriate solutions to correcting for TRE differently for satellite images and SRMs.