HEIGHTS AND DISTANCE
1. Line of sight
A line drawn from the eye of the observer to the point in the object viewed by the observer is called the line of sight.
2. Angle of elevation
The angle of elevation of the point viewed is the angle formed by the line of sight with the horizontal when the point being viewed is above the horizontal-level. In the figure, ∠AOB is the angle of elevation.
3. Angle of depression
The angle of depression of the point viewed is the angle formed by the line of sight with the horizontal level when the point being viewed is below the horizontal level. In the figure, ∠AOC is the angle of depression.
In case of an angle of elevation the observer has to raise his head to look at the object whereas in case of an angle of depression he lowers his head to look at the point being viewed.