Figure 3.
Geometries for distance and size judgments. (a) A line in physical space (blue) of size Sp is located at distance Zp from the observer (arc at the right side). In perspective space, as a model for visual space, the line (red) gets size Sv and distance Zv if the vanishing point is placed at distance VP. (b) A standard line in physical space of fixed size Sps is located at a variable distance Zps from the observer. A comparison line in physical space of adjustable size Spc is located at a fixed distance Zpc from the observer. In visual space, the lines have sizes Svs and Svc, respectively, if the vanishing point is at distance VP. The vertical, dotted lines on the right side of the graphs represent the plane of the observer orthogonal to the viewing direction.