AP_Logger: added logging of GPS yaw

some GPS modules can give true yaw, whether moving or not

libraries/AP_Logger/LogFile.cpp

@@ -138,6 +138,10 @@ void AP_Logger::Write_GPS(uint8_t i, uint64_t time_us)
         time_us = AP_HAL::micros64();
     }
     const struct Location &loc = gps.location(i);
+
+    float yaw_deg=0, yaw_accuracy_deg=0;
+    gps.gps_yaw_deg(i, yaw_deg, yaw_accuracy_deg);
+
     struct log_GPS pkt = {
         LOG_PACKET_HEADER_INIT((uint8_t)(LOG_GPS_MSG+i)),
         time_us       : time_us,
@@ -152,6 +156,7 @@ void AP_Logger::Write_GPS(uint8_t i, uint64_t time_us)
         ground_speed  : gps.ground_speed(i),
         ground_course : gps.ground_course(i),
         vel_z         : gps.velocity(i).z,
+        yaw           : yaw_deg,
         used          : (uint8_t)(gps.primary_sensor() == i)
     };
     WriteBlock(&pkt, sizeof(pkt));

libraries/AP_Logger/LogStructure.h

@@ -212,6 +212,7 @@ struct PACKED log_GPS {
     float    ground_speed;
     float    ground_course;
     float    vel_z;
+    float    yaw;
     uint8_t  used;
 };
 
@@ -1188,10 +1189,10 @@ struct PACKED log_Arm_Disarm {
 #define GPA_MULTS "FBBBB-CF"
 
 // see "struct GPS_State" and "Write_GPS":
-#define GPS_LABELS "TimeUS,Status,GMS,GWk,NSats,HDop,Lat,Lng,Alt,Spd,GCrs,VZ,U"
-#define GPS_FMT   "QBIHBcLLefffB"
-#define GPS_UNITS "s---SmDUmnhn-"
-#define GPS_MULTS "F---0BGGB000-"
+#define GPS_LABELS "TimeUS,Status,GMS,GWk,NSats,HDop,Lat,Lng,Alt,Spd,GCrs,VZ,Yaw,U"
+#define GPS_FMT   "QBIHBcLLeffffB"
+#define GPS_UNITS "s---SmDUmnhnh-"
+#define GPS_MULTS "F---0BGGB000--"
 
 #define GYR_LABELS "TimeUS,SampleUS,GyrX,GyrY,GyrZ"
 #define GYR_FMT    "QQfff"