Corner mirror
A corner mirror is an optical device with which an observer can move his point of view , similar to a periscope .
use
Military technology
Angle mirrors are installed in armored vehicles in order to enable relatively safe observation from the combat area protected by the armor into the terrain. There are fixed and rotatable corner mirrors .
In order to maintain the camouflage, it is necessary in the dark to cover corner mirrors from the observer's side, because otherwise light from the interior of the vehicle can penetrate to the outside.
geodesy
In geodesy , angle prisms (also double pentagon) are used to take orthogonal recordings. Two in a housing one above the other mounted pentagon prisms reflect the light 90 ° to the side, the observer sees two flight bars exactly over each other, it is located in the escape of the straight line between the two flight bars. A third range pole can be sighted through a gap between the two prisms. If all three rods are congruent, the plumb point of the angled prism marks the vertex of the right angle.