Like Jerry I'm not sure what you mean. Line of Sight just means you can physically see the drone so depends on visible conditions, obstructions, and your eyesight. However, in some scenarios, you can also use a spotter with a scope, so that can be a pretty long way beyond the Mk1 eyeball's range.

Best I can think of is given a horizontal distance, X, and an altitude, Y, what is the direct distance. If so, that's basic trig - calculating the hypoteneuse of a right angled triangle:

Z = sq.root (X^2 + Y^2)