AP_Math: Use DEGX100 define instead of hardcoded value (NFC)

libraries/AP_Math/definitions.h

@@ -30,6 +30,9 @@
 #define DEG_TO_RAD      (M_PI / 180.0f)
 #define RAD_TO_DEG      (180.0f / M_PI)
 
+// Centi-degrees to radians
+#define DEGX100 5729.57795f
+
 // GPS Specific double precision conversions
 // The precision here does matter when using the wsg* functions for converting
 // between LLH and ECEF coordinates.
@@ -44,7 +47,7 @@ static const double RAD_TO_DEG_DOUBLE = 1 / DEG_TO_RAD_DOUBLE;
 // radius of earth in meters
 #define RADIUS_OF_EARTH 6378100
 
-// convert a longitude or latitude point to meters or centimeteres.
+// convert a longitude or latitude point to meters or centimeters.
 // Note: this does not include the longitude scaling which is dependent upon location
 #define LATLON_TO_M     0.01113195f
 #define LATLON_TO_CM    1.113195f

libraries/AP_Math/location.cpp

@@ -51,7 +51,7 @@ int32_t get_bearing_cd(const struct Location &loc1, const struct Location &loc2)
 {
     int32_t off_x = loc2.lng - loc1.lng;
     int32_t off_y = (loc2.lat - loc1.lat) / longitude_scale(loc2);
-    int32_t bearing = 9000 + atan2f(-off_y, off_x) * 5729.57795f;
+    int32_t bearing = 9000 + atan2f(-off_y, off_x) * DEGX100;
     if (bearing < 0) bearing += 36000;
     return bearing;
 }