Angles of Elevation, Depression, and Inclination
Angle of Elevation or Depression
The angle of elevation is the "upwards" angle from the horizontal to a line of sight from the observer to some point of interest.
If the angle goes "downwards" it is called an angle of depression.
The angle of elevation from you to the plane is the same as the angle of depression from the plane to you.
Angle of Inclination
The angle formed between any kind of line and the horizontal plane.
Inclination is a more general term used for slopes of roads, roofs, and so on; elevation and depression usually involve an observer's eye.
Inclination can be above or below the horizontal plane.
Example: How high is the kite?
You are flying a kite. The string is 30m long and makes an angle of elevation of 40°.
To find the height (h), we use the sine function:
sin(40°)
= h30m
h
= 30m × sin(40°)
≈ 30m × 0.6428...
≈ 19.28m