Color contour maps are views of the ocular surfaces and their properties . A view is defined by the view axis , which specifies the direction and center of the orthogonal view transformation. The view center is the surface point pierced by the view axis. When the surface is displayed, its view axis is rotated perpendicular to the displayed map, and its view center is rotated to the map center. Two kinds of coordinates planes are associated with the view axis.
Meridional planes contain the view axis.
Lateral planes lie perpendicular to the view axis.