Importance

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Abstract

A system for encoding position-related information in and determining the relative position of a reader from a coded pattern represents the position-related information as modulation patterns that are radially symmetrical about respective center points having known locations. The position modulation patterns in a portion of the coded pattern have angular orientations with respect to a reference orientation which is associated with a reference modulation pattern. Based on the angular orientations of the respective position modulation patterns, the relative position of, for example, a reader in the coded pattern can then be determined. The position modulation patterns are selected to have components that are localized in a Fourier transform domain. An example of a position modulation pattern is a radially symmetrical sinusoidal pattern in which spatial frequency and angular orientation are localized in the magnitude Fourier transform domain. In one embodiment of the present invention, the position information may be encoded in one or more portions of an image by varying a characteristic of one or more elements of the image in accordance with the position and reference modulation patterns. An element may be image pixels, and the coded pattern is represented by variations to the intensities of the pixels. The coded pattern may be reproduced as a grayscale texture or combined with a non-coded image by adding a graininess to the image. To decode the coded pattern the system performs a two-dimensional fast Fourier transform and identifies the spatial frequencies and relative angular orientations associated with the respective modulation patterns. The system then determines relative position by triangulation.

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First Claim