beacon 距离间计算

本文转载自查看原文 2017-07-12 14:54 1348 android 蓝牙

TX power ，用于确定你和beacon之间距离有多近。根据这个值不但可以获得粗略的信息（比如靠近/远离/不在范围内等），也可以获取精确到米的距离，TX power是距离设备1米测得的信号强度值

(1)计算1

 1 public double calculateDistance(int txPower, double rssi) {
 2   if (rssi == 0) {
 3     return -1.0; // if we cannot determine accuracy, return -1.
 4   }
 5   double ratio = rssi*1.0/txPower;
 6   if (ratio < 1.0) {
 7     return Math.pow(ratio,10);
 8   }
 9   else {
10     double accuracy =  (0.89976)*Math.pow(ratio,7.7095) + 0.111;
11     return accuracy;
12   }
13 }

（2）计算2

 1 public double calculateAccuracy (int rssi) {
 2         // d = 10^((abs(RSSI) - A) / (10 * n))
 3 
 4         /***
 5          * d - 计算所得距离
 6 
 7          RSSI - 接收信号强度（负值）
 8 
 9          A - 发射端和接收端相隔1米时的信号强度
10 
11          n - 环境衰减因子
12          */
13 
14         int iRssi = Math.abs(rssi);
15         float power = (iRssi - mTxPower) / (10 * mEnvironmentFactor);
16         double dis = Math.pow(10, power);
17 
18         return dis;
19     }

（3）定义区域

 1 private String getDistance(accuracy) {
 2   if (accuracy == -1.0) {
 3     return "Unknown";
 4   } else if (accuracy < 1) {
 5     return "Immediate";
 6   } else if (accuracy < 3) {
 7     return "Near";
 8   } else {
 9     return "Far";
10   }
11 }

altbeacon内置设备模型以及用于beacon测距的算法中的系数

 1 {
 2   "models":
 3   [
 4     {
 5       "coefficient1": 0.42093,
 6       "coefficient2": 6.9476,
 7       "coefficient3": 0.54992,
 8       "version":"4.4.2",
 9       "build_number":"KOT49H",
10       "model":"Nexus 4",
11       "manufacturer":"LGE"
12     },
13     {
14       "coefficient1": 0.42093,
15       "coefficient2": 6.9476,
16       "coefficient3": 0.54992,
17       "version":"4.4.2",
18       "build_number":"LPV79",
19       "model":"Nexus 5",
20       "manufacturer":"LGE",
21       "default": true
22     },
23     {
24       "coefficient1": 0.9401940951,
25       "coefficient2": 6.170094565,
26       "coefficient3": 0.0,
27       "version":"5.0.2",
28       "build_number":"LXG22.67-7.1",
29       "model":"Moto X Pro",
30       "manufacturer":"XT1115",
31       "default": false
32     },
33     {
34       "coefficient1": 0.1862616782,
35       "coefficient2": 8.235367435,
36       "coefficient3": -0.45324519,
37       "version":"6.0",
38       "build_number":"MPE24.49-18",
39       "model":"XT1092",
40       "manufacturer":"Motorola",
41       "default": false
42     }
43   ]
44 }

ALTBeacon中的测距方法

 1 public double calculateDistance(int txPower, double rssi) {
 2     if (rssi == 0) {
 3         return -1.0; // if we cannot determine accuracy, return -1.
 4     }
 9     double ratio = rssi*1.0/txPower;
10     double distance;
11     if (ratio < 1.0) {
12         distance =  Math.pow(ratio,10);
13     }
14     else {
15         distance =  (mCoefficient1)*Math.pow(ratio,mCoefficient2) + mCoefficient3;
16     }18     return distance;
19 }

如果当前的设备没有在altbeacon内置设备模型列表中，beacon SDK 则选择Nexus 5系数进行距离计算，如下

 1 public static double calculateAccuracy(int txPower, double rssi) {
 2        if (rssi == 0) {
 3            return -1.0; // if we cannot determine accuracy, return -1.
 4        }
 5        double ratio = rssi * 1.0 / txPower;
 6        if (ratio < 1.0) {
 7            return Math.pow(ratio, 10);
 8        } else {
 9            double accuracy = (0.42093) * Math.pow(ratio, 6.9476) + 0.54992;
10            return accuracy;
11        }
12    }

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