Shape perception in 3-D scatterplots using constant visual angle glyphs

When viewing 3-D scatterplots in immersive virtual environments, one commonly encountered problem is the presence of clutter, which obscures the view of any structures of interest in the visualization. In order to solve this problem, we propose to render the 3-D glyphs such that they always cover the the same amount of screen space. For perceptual reasons, we call this approach constant visual angle glyphs, or CVA glyphs. The use of CVA glyphs implies some desirable perceptual consequences, which have not been previously described or discussed in existing literature: CVA glyphs not only have the prospect of dealing with clutter, but also the prospect of allowing for a better perception of the continuous shapes of structures in 3-D scatterplots. In a formal user evaluation of CVA glyphs, the results indicate that such glyphs do allow for better perception of shapes in 3-D scatterplots compared to regular perspective glyphs, especially when a large amount of clutter is present. Furthermore, our evaluation revealed that perception of structures in 3-D scatterplots is significantly affected by the volumetric density of the glyphs in the plot.