The angle framed by the line of sight and the horizontal (line from observer and object vertical point) is known as angle of elevation. It can be estimated from the known values of height and distance of the object. In other words, Angles of elevation or inclination are angles above the horizontal. Like looking up from ground level towards the top of a flagpole. Use this online calculator to find the angle of elevation by entering the values of height and distance of the object.
An aeroplane flies at a height of 100mm, the distance of the plane from the observers point of view is 123mm.
Angle of Elevation = atan (100/123)
= 39.11 degrees.