def calculateDistanceWithRSSI(rssi,beaconnumber):

    beacon = conf.BeaconList[beaconnumber];
    txPower = beacon[7]
    ratio_db = txPower - rssi;
    ratio_linear = pow(10, ratio_db / 10);
    r = pow(ratio_linear, .5);
    return r

def getXYFrom3Beacons(beaconnumbera, beaconnumberb, beaconnumberc, rollingRSSIArray):

    beacona = conf.BeaconList[beaconnumbera];
    beaconb = conf.BeaconList[beaconnumberb];
    beaconc = conf.BeaconList[beaconnumberc];
    xa = float(beacona[2])
    ya = float(beacona[3])
    xb = float(beaconb[2])
    yb = float(beaconb[3])
    xc = float(beaconc[2])
    yc = float(beaconc[3])

    ra = float(calculateDistanceWithRSSI(rollingRSSIArray[beaconnumbera], beaconnumbera ))
    rb = float(calculateDistanceWithRSSI(rollingRSSIArray[beaconnumberb], beaconnumberb ))
    rc = float(calculateDistanceWithRSSI(rollingRSSIArray[beaconnumberc], beaconnumberc ))

    S = (pow(xc, 2.) - pow(xb, 2.) + pow(yc, 2.) - pow(yb, 2.) + pow(rb, 2.) - pow(rc, 2.)) / 2.0
    T = (pow(xa, 2.) - pow(xb, 2.) + pow(ya, 2.) - pow(yb, 2.) + pow(rb, 2.) - pow(ra, 2.)) / 2.0


    try:
        y = ((T * (xb - xc)) - (S * (xb - xa))) / a - yb) * (xb - xc)) - ((yc - yb) * - xa)))
        x = ((y * (ya - yb)) - T) / (xb - xa)

    except ZeroDivisionError as detail:
        print 'Handling run-time error:', detail
        return [-1,-1]

    point = [x, y]
    return point