1. American Meteorological Society [AMS]. (2012). Glossary of meteorology. Retrieved August 11, 2018 from
http://glossary.ametsoc.org/wiki/Horizon
2. Research Note PSW-180;EL Amidon,1968
3. Andersen, K. (2007). Geometry of an art. Dordrecht: Springer.
4. De Floriani, L., & Magillo, P. (1995). Horizon computation on a hierarchical triangulated terrain model. The Visual Computer, 11(3), 134–149.
5. Fisher, P. F. (1991). First experiments in viewshed uncertainty: The accuracy of the viewshed area. Photogrammetric Engineering and Remote Sensing, 57(10), 1321–1327.