worked on signal-strength-estimation

add this information to grid nodes
evaluate this information
new test-cases

sensors/radio/WiFiObservation.h

@@ -0,0 +1,100 @@
+#ifndef WIFIOBSERVATION_H
+#define WIFIOBSERVATION_H
+
+#include <vector>
+#include <fstream>
+
+#include "../MACAddress.h"
+#include "../../math/Distributions.h"
+
+
+/** observed one AP with the given signal strength */
+struct WiFiObservationEntry {
+
+	/** AP's MAC address */
+	MACAddress mac;
+
+	/** AP's RSSI */
+	float rssi;
+
+	/** ctor */
+	WiFiObservationEntry(const MACAddress& mac, const float rssi) : mac(mac), rssi(rssi) {;}
+
+};
+
+/** all observed APs and their signal strength */
+struct WiFiObservation {
+
+	/** one entry per AP */
+	std::vector<WiFiObservationEntry> entries;
+
+};
+
+
+class WiFiObserver {
+
+private:
+
+	float sigma = 8.0f;
+
+public:
+
+	/** ctor */
+	WiFiObserver(const float sigma) : sigma(sigma) {
+		;
+	}
+
+	/**
+	 * get the given GridNode's probability based on the provided WiFi measurements
+	 */
+	template <typename Node> double getProbability(const Node& n, const WiFiObservation& obs, const int age_ms = 0) {
+
+		double prob = 0;
+
+		// sigma grows with measurement age
+		const double sigma = this->sigma * (1 + age_ms / 500.0f);
+
+		// process each observed AP
+		for (const WiFiObservationEntry& ap : obs.entries) {
+
+			// the RSSI from the scan
+			const float measuredRSSI = ap.rssi;
+
+			// the RSSI from the model (if available!)
+			const float modelRSSI = n.getRSSI(ap.mac);
+
+			// no model RSSI available?
+			if (modelRSSI == 0) {continue;}
+
+			// compare both
+			const double p = Distribution::Normal<double>::getProbability(measuredRSSI, sigma, modelRSSI);
+
+			// adjust using log
+			prob += std::log(p);
+
+		}
+
+		//return std::pow(std::exp(prob), 0.1);
+		return std::exp(prob);
+
+	}
+
+	/** gnuplot debug dump */
+	template <typename Node> void dump(Grid<Node>& grid, const WiFiObservation& obs, const std::string& fileName) {
+
+		std::ofstream out(fileName);
+		out << "splot '-' with points palette\n";
+
+		for (const Node& n : grid) {
+			const float p = getProbability(n, obs);
+			out << n.x_cm << " " << n.y_cm << " " << n.z_cm << " " << p << "\n";
+		}
+		out << "e\n";
+
+		out.close();
+
+	}
+
+};
+
+#endif // WIFIOBSERVATION_H