How to make a 3D radar?

I'm trying to make a 3D radar system where pretty much it logs everything with a set range (say x unity world space units), takes their positions and scales it down to a small representation in a sphere. Basically something that looks like this: https://dl.dropboxusercontent.com/u/11090933/FX%20Asset%20Store/FX%203D%20Radar/Logos/Radar_Anatomy_Small.png Just how do you take gameObjects that you tag, give it a texture and instantiate it? I understand that free assets exist for this, but I just want an explanation on how the script would be built, and how it works.