I am trying to automate a calculation of the blocked fraction of a field of view from a point to a shapefile. I.e. find α in

, such that α / 360 gives me the fraction of the field of view covered by the shapefile in reference to the total field of view.

I know ArcGIS features a 'field of view' based on a DEM/raster (right?), but I am looking for a simpler application, between a simple point and polygon shape.

Is anyone aware of software / a function that is able to do this? It is very easy to do by hand, but I need to process roughly 250 cases, so I thought I'd better ask for other suggestions :)


There are three points you need the coordinates for:

  • a = x,y of the viewer location
  • b = x,y of where the view line meets the "top" of the polygon
  • c = x,y of where the view line meets the "bottom" of the polygon

These form a triangle and the solution is just trigonometry:

angle alpha = cos^-1 ( ((b-c)^2+(c-a)^2-(c-b)^2))/(2*((c-b)^2)^(1/2)*((c-a)^2)^(1/2)

*see SSS triangle solutions http://mathworld.wolfram.com/SSSTheorem.html

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.