三边测量法：通过三点坐标和到三点的距离，返回第4点位置

public class IBeaconLocation {

    //计算手机与蓝牙基站的距离
    public static double calculateAccuracy(iBeaconClass.iBeacon beacon) {
        int txPower = beacon.txPower;
        double rssi = beacon.rssi;
        if (rssi == 0) {
            return -1.0; // if we cannot determine accuracy, 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;
        }
    }

    //三边测量法
    // 通过三点坐标和到三点的距离，返回第4点位置
    public double[] calcPhonePosition(double x1, double y1, double d1,
                                      double x2, double y2, double d2,
                                      double x3, double y3, double d3) {
        double[] d = {0.0, 0.0};
        double a11 = 2 * (x1 - x3);
        double a12 = 2 * (y1 - y3);
        double b1 = Math.pow(x1, 2) - Math.pow(x3, 2)
                + Math.pow(y1, 2) - Math.pow(y3, 2)
                + Math.pow(d3, 2) - Math.pow(d1, 2);
        double a21 = 2 * (x2 - x3);
        double a22 = 2 * (y2 - y3);
        double b2 = Math.pow(x2, 2) - Math.pow(x3, 2)
                + Math.pow(y2, 2) - Math.pow(y3, 2)
                + Math.pow(d3, 2) - Math.pow(d2, 2);

        d[0] = (b1 * a22 - a12 * b2) / (a11 * a22 - a12 * a21);
        d[1] = (a11 * b2 - b1 * a21) / (a11 * a22 - a12 * a21);

        return d;

    }

    //double 四舍五入
    public int doubleRound(double num) {
        BigDecimal b = new BigDecimal(num);
        num = b.setScale(0, BigDecimal.ROUND_HALF_UP).doubleValue();
        return (int) num;
    }

}