Merge pull request #978 from PX4/mtk_fix

Mtk fix

src/drivers/gps/mtk.cpp

@@ -249,12 +249,18 @@ MTK::handle_message(gps_mtk_packet_t &packet)
 		warnx("mtk: unknown revision");
 		_gps_position->lat = 0;
 		_gps_position->lon = 0;
+
+		// Indicate this data is not usable and bail out
+		_gps_position->eph_m = 1000.0f;
+		_gps_position->epv_m = 1000.0f;
+		_gps_position->fix_type = 0;
+		return;
 	}
 
 	_gps_position->alt = (int32_t)(packet.msl_altitude * 10); // from cm to mm
 	_gps_position->fix_type = packet.fix_type;
-	_gps_position->eph_m = packet.hdop; // XXX: Check this because eph_m is in m and hdop is without unit
-	_gps_position->epv_m = 0.0; //unknown in mtk custom mode
+	_gps_position->eph_m = packet.hdop / 100.0f; // from cm to m
+	_gps_position->epv_m = _gps_position->eph_m; // unknown in mtk custom mode, so we cheat with eph
 	_gps_position->vel_m_s = ((float)packet.ground_speed) * 1e-2f; // from cm/s to m/s
 	_gps_position->cog_rad = ((float)packet.heading) * M_DEG_TO_RAD_F * 1e-2f; //from deg *100 to rad
 	_gps_position->satellites_visible = packet.satellites;