Calculate Ble device distance with RSSI + TXPowerLevel

calculatebledistance.java

private static double calculateDistance(float txPower, double rssi) {

        if (rssi == 0) {
            return -1.0; // if we cannot determine distance, return -1.
        }

        double ratio = rssi * 1.0 / txPower;

        if (ratio < 1.0) {
            return Math.pow(ratio, 10);
        } else {
            double accuracy = (0.89976) * Math.pow(ratio, 7.7095) + 0.111;
            return accuracy;
        }
    }