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You want to find the three intersection points of three pairs of great circles given a point and a bearing. Formulae for great circle intersections are given here: There's a javascript widget there for testing, and code which you will have to convert to your unstated programming language of choice. There'...


If you're happy with the characteristics of your projection, you should just use ST_Distance(geometry, geometry). In your example you seem to be in UTM, which is a pretty good projection, so why not? It's much much less CPU intensive than the geodetic functions ST_Distance(geography, geography). (Note that ST_Distance_Spheroid() just calls into the same ...


Deduce what is not visible. Suppose you stand at a vertex on the beach, looking at two remote vertices of a neighboring polygon. Then you can assume that any vertex in the whole sector behind these vertices is invisible from this vertex.

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