Add variance reporting (#1135)

Add variance to mqtt

lib/BleFingerprint/BleFingerprint.cpp

@@ -422,6 +422,7 @@ bool BleFingerprint::seen(BLEAdvertisedDevice *advertisedDevice) {
     raw = pow(10, float(get1mRssi() - rssi) / (10.0f * BleFingerprintCollection::absorption));
     filteredDistance.addMeasurement(raw);
     dist = filteredDistance.getDistance();
+    vari = filteredDistance.getVariance();
 
     if (!added) {
         added = true;
@@ -442,6 +443,7 @@ bool BleFingerprint::fill(JsonObject *doc) {
 
     if (isnormal(raw)) (*doc)[F("raw")] = serialized(String(raw, 2));
     if (isnormal(dist)) (*doc)[F("distance")] = serialized(String(dist, 2));
+    if (isnormal(vari)) (*doc)[F("var")] = serialized(String(vari, 2));
     if (close) (*doc)[F("close")] = true;
 
     (*doc)[F("int")] = (millis() - firstSeenMillis) / seenCount;

lib/BleFingerprint/BleFingerprint.h

@@ -132,7 +132,7 @@ class BleFingerprint {
     int rssi = NO_RSSI;
     int8_t calRssi = NO_RSSI, bcnRssi = NO_RSSI, mdRssi = NO_RSSI, asRssi = NO_RSSI;
     unsigned int qryAttempts = 0, qryDelayMillis = 0;
-    float raw = 0, dist = 0, lastReported = 0, temp = 0, humidity = 0;
+    float raw = 0, dist = 0, vari = 0, lastReported = 0, temp = 0, humidity = 0;
     unsigned long firstSeenMillis, lastSeenMillis = 0, lastReportedMillis = 0, lastQryMillis = 0;
     unsigned long seenCount = 1, lastSeenCount = 0;
     uint16_t mv = 0;

lib/BleFingerprint/FilteredDistance.cpp

@@ -7,7 +7,7 @@
 #include <vector>
 
 FilteredDistance::FilteredDistance(float minCutoff, float beta, float dcutoff)
-    : minCutoff(minCutoff), beta(beta), dcutoff(dcutoff), x(0), dx(0), lastDist(0), lastTime(0), total(0), readIndex(0) {
+    : minCutoff(minCutoff), beta(beta), dcutoff(dcutoff), x(0), dx(0), lastDist(0), lastTime(0), total(0), totalSquared(0), readIndex(0) {
 }
 
 void FilteredDistance::initSpike(float dist) {
@@ -15,12 +15,17 @@ void FilteredDistance::initSpike(float dist) {
         readings[i] = dist;
     }
     total = dist * NUM_READINGS;
+    totalSquared = dist * dist * NUM_READINGS; // Initialize sum of squared distances
 }
 
 float FilteredDistance::removeSpike(float dist) {
     total -= readings[readIndex];                // Subtract the last reading
-    readings[readIndex] = dist;              // Read the sensor
+    totalSquared -= readings[readIndex] * readings[readIndex]; // Subtract the square of the last reading
+
+    readings[readIndex] = dist;                  // Read the sensor
     total += readings[readIndex];                // Add the reading to the total
+    totalSquared += readings[readIndex] * readings[readIndex]; // Add the square of the reading
+
     readIndex = (readIndex + 1) % NUM_READINGS;  // Advance to the next position in the array
 
     auto average = total / static_cast<float>(NUM_READINGS);  // Calculate the average
@@ -62,3 +67,9 @@ float FilteredDistance::getAlpha(float cutoff, float dT) {
     float tau = 1.0f / (2 * M_PI * cutoff);
     return 1.0f / (1.0f + tau / dT);
 }
+
+const float FilteredDistance::getVariance() const {
+    float mean = total / static_cast<float>(NUM_READINGS);
+    float meanOfSquares = totalSquared / static_cast<float>(NUM_READINGS);
+    return meanOfSquares - (mean * mean); // Variance formula: E(X^2) - (E(X))^2
+}

lib/BleFingerprint/FilteredDistance.h

@@ -4,7 +4,7 @@
 #include <Arduino.h>
 
 #define SPIKE_THRESHOLD 1.0f  // Threshold for spike detection
-#define NUM_READINGS 10       // Number of readings to keep track of
+#define NUM_READINGS 12       // Number of readings to keep track of
 
 class FilteredDistance {
    public:
@@ -12,6 +12,8 @@ class FilteredDistance {
     void addMeasurement(float dist);
     const float getMedianDistance() const;
     const float getDistance() const;
+    const float getVariance() const;
+
     bool hasValue() const { return lastTime != 0; }
 
    private:
@@ -27,6 +29,7 @@ class FilteredDistance {
     float readings[NUM_READINGS];  // Array to store readings
     int readIndex;                 // Current position in the array
     float total;                   // Total of the readings
+    float totalSquared;            // Total of the squared readings
 
     void initSpike(float dist);
     float removeSpike(float dist);

ui/src/routes/Fingerprints.svelte

@@ -31,6 +31,14 @@
             sortable: true,
             class: "px-0 py-0 whitespace-nowrap",
         },
+        {
+            key: "var",
+            title: "Var",
+            value: (v) => v.var ?? 0,
+            renderValue: (v) => v.var === undefined ? "n/a" : `${v.var?.toLocaleString(undefined, { minimumFractionDigits: 2 })} m`,
+            sortable: true,
+            class: "px-0 py-0 whitespace-nowrap",
+        },
         {
             key: "id",
             title: "ID",