Fixed bug in MAVLink HIL interface, now consistent with in-flight results in the field

apps/mavlink/mavlink_receiver.c

@@ -485,13 +485,17 @@ handle_message(mavlink_message_t *msg)
 //			hil_gps.counter_pos_valid = hil_counter++;
 			hil_gps.eph_m = (float)gps.eph * 1e-2f; // from cm to m
 			hil_gps.epv_m = (float)gps.epv * 1e-2f; // from cm to m
-			hil_gps.s_variance_m_s = 100; // XXX 100 m/s variance?
-			hil_gps.p_variance_m = 100; // XXX 100 m variance?
+			hil_gps.s_variance_m_s = 5.0f;
+			hil_gps.p_variance_m = hil_gps.eph_m * hil_gps.eph_m;
 			hil_gps.vel_m_s = (float)gps.vel * 1e-2f; // from cm/s to m/s
-			hil_gps.vel_n_m_s = (float)gps.vel * 1e-2f * cosf(gps.cog * M_DEG_TO_RAD_F * 1e-2f);
-			hil_gps.vel_e_m_s = (float)gps.vel * 1e-2f * sinf(gps.cog * M_DEG_TO_RAD_F * 1e-2f);
+
+			/* gps.cog is in degrees 0..360 * 100, heading is -PI..PI */
+			float heading_rad = gps.cog * M_DEG_TO_RAD_F * 1e-2f - M_PI_F;
+			hil_gps.vel_n_m_s = (float)gps.vel * 1e-2f * cosf(heading_rad);
+			hil_gps.vel_e_m_s = (float)gps.vel * 1e-2f * sinf(heading_rad);
 			hil_gps.vel_d_m_s = 0.0f;
-			hil_gps.cog_rad = gps.cog * M_DEG_TO_RAD_F * 1e-2f; // from deg*100 to rad
+			/* COG (course over ground) is speced as 0..360 degrees (compass) */
+			hil_gps.cog_rad = cog_rad + M_PI_F; // from deg*100 to rad
 			hil_gps.fix_type = gps.fix_type;
 			hil_gps.satellites_visible = gps.satellites_visible;