Triangulating distance when recovering ammunition is not feasible(lakes, long distances in fields, etc.)

I have not tried this yet, I just learned how to do it.
I'd be interested to hear if anyone else has done it, and how easy/accurate it is.

This requires two people, the slinger and an observer, both with compasses.
the observer walks a measured distance away, at a known heading.


After throwing, both watch for the landing and take as good a heading as they can on the landing point with their compasses.
this allows us to find the angles between the landing point and both observers.


We construct a triangle with a human at two vertices, the shot landing point at the third.

Assuming an arbitrary firing angle A, heading B from friend to landing position, distance between slinger and friend c, angle from ammo to both humans C
capital letters are angles, lower case are line segments
     C
    * *
    *  *
   *   *
   *    *    
  *     *
  *      *
a       b
*        *
*         *
A**c**B


We can use the law of sines to get the stone travel distance

the non-measured angle C = 180-A-B
a / sin(A) = b / sin(B) = c / sin(C)
we know angle C and distance c, we need distance A
a / sin(A) = c / sin(C)
cross multiply
a * sin(C) = c * sin(A)
isolate a
a = c * sin(A) / sin(C)



If angle A is close enough to 90, we can make things simpler by assuming a right triangle.
unless I'm doing this wrong, an angle of 64.1 degrees is only a drop of 10% distance perpendicular to the base. maybe you could even guess the angle and correct this method accordingly

cos(A)*distance between people = shot range

Here's the video from which I just learned to do this, might be easier to follow.
https://www.youtube.com/watch?v=xvGvgTSkOiw