Calculate the Width of a Visible Object on the Ground

Calculator for the width or breadth of something like a river or so, which is flat on the ground and is watched from a certain height. This calculation is correct, when the distance to the object and the object itself have a size so that the curvature of the earth is negligible. For rivers with a width of up to a few dozend meters or smaller things, this is the case. The difficulty is measuring the angles, if you don't have a sextant or similar equipment.

The eye height h is the height of the eyes above a flat ground. The horizontal distance l is the distance of the eyes projected vertically to the ground to the closer, front edge of the object. Instead of meters (m), you can also use feet or every other unit of length, as long as it is the same unit for all lengths.

Formulas:
γ = α − β
d = √ h² + l²
b = d * sin(γ) / sin(β)

Eye height h:		m
Horizontal distance l:		m
Angle to the front edge α:		°
Angle to the back edge β:		°

Breadth angle γ:		°
Distance eye - object d:		m
Objekt width b:		m