Mavros: "Keine Satelliten" von "/diagnostik" mavros

Ich habe meine Drohne im offenen Bereich platziert und die LED von Pixhawk ist grün.
Nachdem ich diesen Code ausgeführt habe
roslaunch mavros px4.launch
und dann laufe ich
rostopic echo -n1 /diagnostics
ich habe das gefunden

name: "mavros: GPS"
    message: "No satellites"
    hardware_id: "/dev/ttyUSB0:57600"
    values: 
      - 
        key: "Satellites visible"
        value: "0"

Aber nachdem ich qgroundcontrol verbunden und das Programm beendet habe, damit ich mavros starte und die "/diagnostics" erneut überprüfe, habe ich die GPS-Show gefunden.

level: 0
    name: "mavros: GPS"
    message: "3D fix"
    hardware_id: "/dev/ttyUSB0:57600"
    values: 
      - 
        key: "Satellites visible"
        value: "16"
      - 
        key: "Fix type"
        value: "3"

Ich möchte den Wert von GPS abrufen, ohne QGC anschließen zu müssen. Wie kann ich das machen?

MAVROS-Version und -Plattform

Mavros: 0.25.1
ROS: Kinetisch
Ubuntu: 16.04

Autopilot-Typ und -Version

PX4

Version: neueste

Diagnose

header: 
  seq: 327
  stamp: 
    secs: 1527908144
    nsecs:  63593259
  frame_id: ''
status: 
  - 
    level: 0
    name: "mavros: FCU connection"
    message: "connected"
    hardware_id: "/dev/ttyUSB0:57600"
    values: 
      - 
        key: "Received packets:"
        value: "5340"
      - 
        key: "Dropped packets:"
        value: "0"
      - 
        key: "Buffer overruns:"
        value: "0"
      - 
        key: "Parse errors:"
        value: "0"
      - 
        key: "Rx sequence number:"
        value: "240"
      - 
        key: "Tx sequence number:"
        value: "141"
      - 
        key: "Rx total bytes:"
        value: "132922"
      - 
        key: "Tx total bytes:"
        value: "133365"
      - 
        key: "Rx speed:"
        value: "305.000000"
      - 
        key: "Tx speed:"
        value: "320.000000"
  - 
    level: 2
    name: "mavros: GPS"
    message: "No satellites"
    hardware_id: "/dev/ttyUSB0:57600"
    values: 
      - 
        key: "Satellites visible"
        value: "0"
      - 
        key: "Fix type"
        value: "0"
      - 
        key: "EPH (m)"
        value: "Unknown"
      - 
        key: "EPV (m)"
        value: "Unknown"
  - 
    level: 0
    name: "mavros: Heartbeat"
    message: "Normal"
    hardware_id: "/dev/ttyUSB0:57600"
    values: 
      - 
        key: "Heartbeats since startup"
        value: "415"
      - 
        key: "Frequency (Hz)"
        value: "0.960080"
      - 
        key: "Vehicle type"
        value: "Quadrotor"
      - 
        key: "Autopilot type"
        value: "ArduPilotMega / ArduCopter"
      - 
        key: "Mode"
        value: "STABILIZE"
      - 
        key: "System status"
        value: "Standby"
  - 
    level: 0
    name: "mavros: System"
    message: "Normal"
    hardware_id: "/dev/ttyUSB0:57600"
    values: 
      - 
        key: "Sensor present"
        value: "0x00000000"
      - 
        key: "Sensor enabled"
        value: "0x00000000"
      - 
        key: "Sensor helth"
        value: "0x00000000"
      - 
        key: "CPU Load (%)"
        value: "0.0"
      - 
        key: "Drop rate (%)"
        value: "0.0"
      - 
        key: "Errors comm"
        value: "0"
      - 
        key: "Errors count #1"
        value: "0"
      - 
        key: "Errors count #2"
        value: "0"
      - 
        key: "Errors count #3"
        value: "0"
      - 
        key: "Errors count #4"
        value: "0"
  - 
    level: 2
    name: "mavros: Battery"
    message: "No data"
    hardware_id: "/dev/ttyUSB0:57600"
    values: 
      - 
        key: "Voltage"
        value: "-1.00"
      - 
        key: "Current"
        value: "0.0"
      - 
        key: "Remaining"
        value: "0.0"
  - 
    level: 2
    name: "mavros: Time Sync"
    message: "No events recorded."
    hardware_id: "/dev/ttyUSB0:57600"
    values: 
      - 
        key: "Timesyncs since startup"
        value: "0"
      - 
        key: "Frequency (Hz)"
        value: "0.000000"
      - 
        key: "Last dt (ms)"
        value: "3.333722"
      - 
        key: "Mean dt (ms)"
        value: "0.000000"
      - 
        key: "Last system time (s)"
        value: "916.671332000"
      - 
        key: "Time offset (s)"
        value: "1527907227.282750130"

ID prüfen

OK. I got messages from 1:1.

---
Received 165 messages, from 1 addresses
sys:comp   list of messages
  1:1     0, 111