In spite of this positive evidence there are also reported users' comments about disorientation [1, 5]. Specific comments are vague but complain about such things as sudden moves, not seeing how the image changed, expressing doubts as to whether the rescaled image is actually of the same information and even more vague comments about the images not being `right'. One possible explanation is that the disorientation occurs when the modified visual image conflicts with the users' prior mental memory representation of the image. Some types of visual information such as maps assume that distance is to scale and that scale is consistent. However, a multi-scale view will result in regions of varying scale. Previous knowledge about the map may protect the user from assimilating false information but causes disorientation. In unfamiliar information spaces there is an actual chance of misforming.
Use of a spatial metaphor with low level visual cues helps make the distortions present in a multi-scale view understandable. This support will allow users to maintain an accurate mental representation, learning that the information is not impaired by the distortion.
Ideally these visual cues should not interfere with interpreting the actual information, or create a significant drain on cognitive processing. Presently the user has the option of appling either shading or a grid. %This indicates the use of a low level visual skills. Considering the extensive literature establishing that humans can discern three-dimensional shape from shading alone [4], and the considerable evidence to support the fact that this is a low level precognitive skill, shading should give an intuitive impression of the 3D shape. Such a low level visual routine will interfere less with conscious processing and may even provide an aspect of the interface that requires no learning [6]. The second choice of a regular grid reveals the shape of the distortion by accessing two depth cues: it provides perspective information without requiring edges and serves as a texture gradient. Furthermore, the shape and size of the grid squares give an approximate quantitative reading about relative magnification and distortion. As this use of a grid parallels use of a reference grid in cartography its interpretation will be familiar to many.
Figure 1. Undistorted map of Vancouver area |
Figure 2. Vancouver area with four focal points |
Figure 3. Distortion revealed by the grid |
Figure 4. Distortion revealed by shading |
Figures 1, 2, 3 and 4 show the Vancouver area with four focal points. The contrast between the images with and without distortion clues demonstrates how either the shading or the grid can disambiguate the distortions.
There are a whole suite of perceptual cues through which humans establish three dimensions. At this point shading and grids are included in 3DPS. We intend to study to what extent these two cues reveal the 3-dimensional form of the distortions. We are also interested in how successfully users map different aspects of the information, for instance distance, to the distorted surface. Presently only very simple shading is included, it may be necessary to extend to shading model for it to be truly effective.
This research was suported by NSERC and the Algorithms Lab, the Graphics and Multimedia Research Lab and the School of Computing Science, S.F.U.