[Cartographic errors in perimetry]

Abstract

Cartography in perimetry repeats the problem of the cartography of the globe: it is impossible to transfer the image properly without a distortion of either angles, distances or areas. The projection type mostly used in perimetry leads to an enlargement and a tangential deformation that increases overproportionally towards the periphery (30 degrees: +5%, 60 degrees: +20%, 90 degrees: +57%). A circular scotoma, for example, is charted as en ellipse. In the opposite case, when a test point pattern is transferred from the perimetric chart to a perimetric sphere, there is a deformation, too. The distances between the test points are reduced in tangential direction, compared to the chart. A test grid with equidistant points on the chart appears in a rhomboid or rectangular distortion. This phenomenon has to be considered in the design of test point patterns for automatic static perimeters.