# Base point

Base of a perpendicular on a straight line${\ displaystyle F}$${\ displaystyle g}$

In geometry , the base point of a perpendicular from a point to a straight line or a plane is always the point at which the perpendicular meets the straight line or the plane.

In visual perception, foot points are of no small importance. On a plane lying in front of the viewer, base points of objects at different distances appear at different heights. In particular, the same distances can be easily recognized. Unrecognizable differences in height of the terrain can appear to simulate the same or different base positions of the objects with the consequence of size delusions.

In the horizon system , the base point opposite the zenith is called the nadir .