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. Author manuscript; available in PMC: 2009 Oct 13.
Published in final edited form as: J Vis. 2006 May 5;6(5):634–648. doi: 10.1167/6.5.8

Figure 3. Coordinate systems.

Figure 3

Cartesian coordinate system was used in defining surface patches. The z-axis lies along the line of sight from the observer to the origin such that the observer’s gaze is in the -z direction. The x-axis lies along the horizontal line tangential to the surface and the y-axis lies along the vertical line tangential to the surface. For the punctate illuminant positions, spherical coordinates were used. The illuminant had an elevation ϕ (relative to the surface) and azimuth ψ, and was located at a distance d from the surface patch. In this study, ϕ was varied while ψ and d were fixed at 180° and 80 cm, respectively. The origin of the coordinate system was the center of the surface patch. The observer was always at (x,y,z) = (0,0,70 cm) or, in spherical coordinates, (ψ ϕr)= (90°,−,70 cm).