Arduino - Ir Communications over long rang?

interesting. Okay here my problem my problem with my project. I know there is other ways of doing this. But I'm building a IR communications between two arduino. The problem is I need to figure out how far from the Transmitting arduino to the Receiving arduino. I Don't know how to figure out far they are apart from each other or If the transmitter IR is to the left a little of the receiver Basic more like tracking i guess you can say.