Add support for BMX160/RAK12034 compass module (#4021)

src/Fusion/FusionCompass.c

@@ -0,0 +1,51 @@
+/**
+ * @file FusionCompass.c
+ * @author Seb Madgwick
+ * @brief Tilt-compensated compass to calculate the magnetic heading using
+ * accelerometer and magnetometer measurements.
+ */
+
+//------------------------------------------------------------------------------
+// Includes
+
+#include "FusionCompass.h"
+#include "FusionAxes.h"
+#include <math.h> // atan2f
+
+//------------------------------------------------------------------------------
+// Functions
+
+/**
+ * @brief Calculates the magnetic heading.
+ * @param convention Earth axes convention.
+ * @param accelerometer Accelerometer measurement in any calibrated units.
+ * @param magnetometer Magnetometer measurement in any calibrated units.
+ * @return Heading angle in degrees.
+ */
+float FusionCompassCalculateHeading(const FusionConvention convention, const FusionVector accelerometer,
+                                    const FusionVector magnetometer)
+{
+    switch (convention) {
+    case FusionConventionNwu: {
+        const FusionVector west = FusionVectorNormalise(FusionVectorCrossProduct(accelerometer, magnetometer));
+        const FusionVector north = FusionVectorNormalise(FusionVectorCrossProduct(west, accelerometer));
+        return FusionRadiansToDegrees(atan2f(west.axis.x, north.axis.x));
+    }
+    case FusionConventionEnu: {
+        const FusionVector west = FusionVectorNormalise(FusionVectorCrossProduct(accelerometer, magnetometer));
+        const FusionVector north = FusionVectorNormalise(FusionVectorCrossProduct(west, accelerometer));
+        const FusionVector east = FusionVectorMultiplyScalar(west, -1.0f);
+        return FusionRadiansToDegrees(atan2f(north.axis.x, east.axis.x));
+    }
+    case FusionConventionNed: {
+        const FusionVector up = FusionVectorMultiplyScalar(accelerometer, -1.0f);
+        const FusionVector west = FusionVectorNormalise(FusionVectorCrossProduct(up, magnetometer));
+        const FusionVector north = FusionVectorNormalise(FusionVectorCrossProduct(west, up));
+        return FusionRadiansToDegrees(atan2f(west.axis.x, north.axis.x));
+    }
+    }
+    return 0; // avoid compiler warning
+}
+
+//------------------------------------------------------------------------------
+// End of file