fixed some compiler warnings

added equality checks to sensor-data classes
more robust sensor reader [fixed some issues]
added support for gps
added support for compass
added sensor-data-writer
added test-cases
minor changes

sensors/imu/CompassData.h

@@ -0,0 +1,56 @@
+#ifndef COMPASSDATA_H
+#define COMPASSDATA_H
+
+
+#include <cmath>
+#include <sstream>
+
+
+/** data received from a compass sensor */
+struct CompassData {
+
+	/** azimuth angle. NAN if not available */
+	float azimuth = NAN;
+
+	/** describes the sensor's quality */
+	float quality01 = 0;
+
+
+	/** empty ctor */
+	CompassData() : azimuth(NAN) {;}
+
+	/** data ctor */
+	CompassData(const float azimuth) : azimuth(azimuth), quality01(0) {;}
+
+	/** data ctor */
+	CompassData(const float azimuth, const float quality01) : azimuth(azimuth), quality01(quality01) {;}
+
+	/** get an instance describing invalid data */
+	static CompassData INVALID() {
+		return CompassData(NAN);
+	}
+
+	/** convert to string */
+	std::string asString() const {
+		std::stringstream ss;
+		ss << "(" << azimuth << ")";
+		return ss.str();
+	}
+
+	/** is the compass data valid? [compass present] */
+	bool isValid() const {
+		return azimuth == azimuth;
+	}
+
+	bool operator == (const CompassData& o) const {
+		return	EQ_OR_NAN(azimuth, o.azimuth) &&
+				EQ_OR_NAN(quality01, o.quality01);
+	}
+
+private:
+
+	static inline bool EQ_OR_NAN(const float a, const float b) {return (a==b) || ( (a!=a) && (b!=b) );}
+
+};
+
+#endif // COMPASSDATA_H