Conditional probability on a localization program.

Hello,

As the title says, I want to know how I can calculate the P(IsThere|BeenThere).

I'll elaborate:

In this program I have, I sense the wi-fi signal and import it to matlab. With this, I made a fingerprinting plant with the location (X,Y, SignalOfAp1, signalOfAP2,...) and that map with fingerprinting is my reference map.

In the program, I am measuring the signal I receive and comparing it with the fingerprinting map I just mentioned to know where I'm localized in the map.

This is made calculating a probability using a gaussian distribution.

So, What i end up having is the probability of being In (Xcoordinate,Ycoordinate) and the probability of being in the (X,Y) of WHERE I WAS BEFORE.

                                      P(Isthere /\ BeenThere)
so i know the P(IsThere|BeenThere) = --------------------------
                                            P(BeenThere)

And I don't know how to calculate the: P(Isthere /\ BeenThere)

I'm sorry if i'm lacking some logic here and if you dont understand something, This is the best i could explain.

Thank you very much