Protests and online activism in recent months have brought a resurgence of ethnic Oromo nationalism in Ethiopia. 01 Aug 2014 12:37 GMT | Human Rights, Africa, Ethiopia. Oromo students protested against a government plan to expand Addis Ababa [Jawar Mohammed/Al Jazeera]
You just have to substitute values of slope and vertical distance in formula and get value of horizontal distance. Similarly, any one of them can be found if other two are given. For instance, if you have a slope given in Percentage as 10 % and a vertical distance of 50 feet, then equation will look like:
From the figure above, simple geometry gives the horizontal field of view. where width is the horizontal width of the sensor (projection plane). So for example, for a 35mm film (frame is 24mm x 36mm), and a 20mm (focal length) lens, the horizontal aperture would be almost 84 degrees (vertical aperture of 62 degrees).