Polyfocal display

The Polyfocal display was proposed by Naftali Kadmon and Eli Shlomi [Kadmon and Shlomi, 1978] for presentation of statistical data on cartographic maps.

Polyfocal display is an interactive technique that allows to selectively zoom into sections of an image. Scaling is described by a (two–dimensional) magnification function, providing for generating several foci — each having induvidual magnification–parameters and correspondingly adjustable distortion in the regions further away from the focus.

The Polyfocal Display function defines an area for a focal point as a location of high radial magnification accentuated by a surrounding area of decreased magnification. Two parameters define the level of distortion found in the resulting transformation. The first parameter controls the level of magnification at the focal point, whereas the second one controls the rate of change of magnification with distance from the point of focus (Leong). Multifocal polyfocal displays also exist, in which more than one focal point is specified.

[Gerstmann, 2001]

File:Magnificationfunction.jpg

Magnification function

References

• [Gerstmann, 2001]: Derek Gerstmann, Advanced Visual Interfaces for Hierarchical Structures, 2001.
• [Leung and Apperley, 1994] Y. K. Leung and M. D. Apperley. A review and taxonomy of distortion-oriented presentation techniques. ACM Transactions Computer-Human Interaction, 1(2):126-160, June 1994.
• [Kadmon and Shlomi, 1978] Naftali Kadmon and Eli Shlomi, A polyfocal projection for statistical surfaces. Cartography, 15(1):36-41, 1978.