Object only visible when in a certain PCO

[Vilespring]

I'm thinking of a way of doing artillery, where the gunner views the battlefield from a tactical view over-head, can see a brightly colored ring where the shell could land. I was thinking that each dot be the result of a projectile that is on the max deviation of the gun, and when it hits the ground, it produces a bright color. Then there would be gravity modifiers on the near instant projectile, so it would predict were the shell would land, rather well.

My question is, how do I make the target reticule only visible to the gunner, so that the people around don't know a shell is about to land there?