LM3S1968: Add first example project.

[bertos.git] / boards / ek-lm3s1968 / examples / gps / compass.c

diff --git a/boards/ek-lm3s1968/examples/gps/compass.c b/boards/ek-lm3s1968/examples/gps/compass.c
new file mode 100644 (file)
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+++ b/boards/ek-lm3s1968/examples/gps/compass.c
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+#include <cfg/compiler.h>
+#include <cfg/debug.h>
+#include <math.h>
+#include "compass.h"
+
+static const char *_compass_heading[] =
+{
+       "N", "NNE", "NE", "ENE",
+       "E", "ESE", "SE", "SSE",
+       "S", "SSW", "SW", "WSW",
+       "W", "WNW", "NW", "NNW",
+};
+
+/**
+ * Use the Haversine formula to calculate great-circle distances between the
+ * two points.
+ *
+ * The Haversine formula remains particularly well-conditioned for numerical
+ * computation even at small distances, unlike calculations based on the
+ * spherical law of cosines.
+ */
+float distance(float lat1, float lon1, float lat2, float lon2)
+{
+       const float PLANET_RADIUS = 6371000;
+       float d_lat = deg2rad(lat2 - lat1);
+       float d_lon = deg2rad(lon2 - lon1);
+
+       float a = sin(d_lat / 2) * sin(d_lat / 2) +
+                       cos(deg2rad(lat1)) * cos(deg2rad(lat2)) *
+                       sin(d_lon / 2) * sin(d_lon / 2);
+       float c = 2 * atan2(sqrt(a), sqrt(1 - a));
+
+       return PLANET_RADIUS * c;
+}
+
+/**
+ * Evaluate the bearing (also known as forward azimuth) using spherical law
+ * coordinates.
+ *
+ * The bearing is a straight line along a great-circle arc from the start point
+ * to the destination point.
+ */
+int bearing(float lat1, float lon1, float lat2, float lon2)
+{
+       float res;
+
+       res = rad2deg(atan2(sin(deg2rad(lon2 - lon1)) *
+               cos(deg2rad(lat2)), cos(deg2rad(lat1)) *
+               sin(deg2rad(lat2)) - sin(deg2rad(lat1)) *
+               cos(deg2rad(lat2)) * cos(deg2rad(lon2) -
+               deg2rad(lon1))));
+       return ((int)res + 360) % 360;
+}
+
+const char *compass_heading(int bearing)
+{
+       ASSERT(bearing >= 0 && bearing < 360);
+       /*
+        * bearing / 22.5
+        */
+       return _compass_heading[(bearing << 4) / 360];
+}