Andruav GPS Injection

Your drone-side phone already has a capable multi-constellation GNSS receiver. With GPS Injection, Andruav sends the phone’s GPS fix to the ArduPilot flight controller over MAVLink (GPS_INPUT), so the flight controller can use the phone as its GPS — either as its only GPS, or as a second GPS next to a real receiver.

GPS Injection

Warning

A phone’s GPS is usually less accurate than a dedicated GPS module — phones typically report 5–15 m horizontal accuracy even under open sky. Test on the ground (or in SITL) before you rely on it in flight, and keep a safe non-GPS flight mode ready.

Requirements

  • The drone-side phone runs Andruav on Android 8.0 (Oreo) or later — the option is disabled on older Android versions.

  • The phone has GNSS hardware and Andruav has precise location permission.

  • Andruav is connected to an ArduPilot flight controller — see Andruav Getting Started.

  • The phone has a clear view of the sky. Indoors the phone usually has no GPS fix, and Andruav then sends nothing.

Step 1 — Configure the flight controller

Set the flight controller’s GPS type to MAVLink (14) with Mission Planner or QGroundControl, then reboot the flight controller.

Parameter

Value

Use

GPS1_TYPE (ArduPilot 4.6+) or GPS_TYPE (older)

14

The phone is the primary GPS.

GPS2_TYPE (ArduPilot 4.6+) or GPS_TYPE2 (older)

14

The phone is a second GPS next to a real GPS receiver.

Tip

Calibrate the compass with the phone mounted in its final position. A phone close to the compass disturbs it, and ArduPilot will then refuse to arm with PreArm: Check mag field.

Step 2 — Enable GPS Injection in Andruav

On the drone-side phone open Drone Settings → FCB & Telemetry and enable GPS Injection.

GPS Injection preference

Once the flight controller is connected, the GPS Injection description shows whether the flight controller will accept the phone’s GPS:

  • ✓ Flight controller GPS1_TYPE is set to MAVLink (14) — ready.

  • ⚠ Flight controller is not set to receive it: GPS_TYPE=…, GPS_TYPE2=… — go back to Step 1; until the GPS type is 14 the injected GPS is ignored.

Related options in the same section:

  • Ignore Mobile Sensors must be off — it switches the phone’s GPS off, so the two options cannot be enabled together.

  • Inject Heading also sends the phone’s compass heading as the vehicle yaw. Leave it off unless the phone is rigidly fixed to the airframe with a known orientation — a loose or handheld phone feeds the flight controller a false heading.

Step 3 — Check that the flight controller uses the phone GPS

Receiving the phone’s GPS and using it are two different things. Watch the flight controller messages in your ground station:

  1. GPS 1: detected MAV — the flight controller receives Andruav’s GPS.

  2. EKF3 IMU0 is using GPS and EKF3 IMU0 origin set — the position estimator accepted it.

  3. Home is set at the phone’s location and position flight modes can arm.

ArduPilot’s position estimator (EKF3) only accepts a GPS after all of these checks pass continuously for 10 seconds:

Check

Limit (default)

Mission Planner Status field

Satellites used

6 or more

satcount

HDOP

2.5 or less

gpshdop

Horizontal accuracy

5 m or less

gpsh_acc

Vertical accuracy

7.5 m or less

gpsv_acc

Speed accuracy

1.0 m/s or less

gpsvel_acc

Until then the ground station shows PreArm: Need Position Estimate or PreArm: AHRS: waiting for home.

When the phone’s accuracy is not good enough

The most common blocker is horizontal accuracy. Phones often report about 10 m even next to a window with 40 satellites and an excellent HDOP, which is above EKF3’s 5 m limit — the flight controller then waits for home forever. You have two options, both set on the flight controller:

  • EK3_CHECK_SCALE = 200 doubles the accuracy limits (horizontal 10 m).

  • EK3_GPS_CHECK = 23 disables only the position-accuracy check and keeps the satellite, HDOP, speed-accuracy and yaw checks (default is 31).

Warning

Relaxing these checks means the vehicle navigates on a position estimate that may be off by 10 m or more. Use EK3_GPS_CHECK = 23 for bench and SITL testing; on a real vehicle decide deliberately, and fly position modes with that error in mind.

How Andruav sends the GPS

  • 10 times per second. ArduPilot marks a GPS unhealthy below about 5 Hz, while a phone produces about one fix per second, so Andruav re-sends the latest fix at 10 Hz.

  • Real GPS fixes only. Wi-Fi and cell-tower locations are never sent to the flight controller. The app’s own map and server location still use them as before.

  • Stops on a lost fix. If the phone has no new GPS fix for 2 seconds, Andruav stops sending; the flight controller reports the GPS lost after 4 seconds.

  • Honest data. Satellites used in the fix, the phone’s reported accuracies, north/east velocity and altitude above mean sea level are sent. Values the phone does not report are marked as unavailable rather than sent as zero.

  • Heading only on request. Yaw is sent only with Inject Heading enabled.

Testing GPS Injection with SITL

You can test the whole chain on a desk with ArduPilot SITL (see Andruav Simulation using SITL). Two things differ from a normal SITL session:

  • SITL’s own simulated GPS must be switched off, otherwise the test proves nothing.

  • SITL must start at the phone’s location. SITL simulates its compass for its own start location; if that is far from the phone, arming fails with PreArm: Check mag field.

Create a parameter file andruav_gps_inject.parm:

GPS1_TYPE        14
GPS_TYPE         14
SIM_GPS1_ENABLE  0
SIM_GPS_DISABLE  1
LOG_DISARMED     1
EK3_GPS_CHECK    23

Both the old and the new parameter names are listed so the same file works with older and newer ArduPilot versions. EK3_GPS_CHECK 23 lets a desk test pass with the phone’s typical ~10 m accuracy.

Start SITL at the phone’s latitude, longitude and altitude:

cd ~/ardupilot
build/sitl/bin/arducopter --model + --speedup 1 -I 0 \
    --home <phone_lat>,<phone_lng>,<altitude_msl>,0 \
    --serial1 udpclient:127.0.0.1:14550 \
    --defaults Tools/autotest/default_params/copter.parm,andruav_gps_inject.parm

SITL waits with Waiting for connection .... until a client connects on TCP port 5760. In Andruav’s FCB connection screen choose WiFi/TCP and connect to <computer_ip>:5760. A ground station can watch at the same time on UDP port 14550.

Note

Andruav does not reconnect automatically when SITL restarts — connect again from the FCB screen after every SITL restart.

Troubleshooting

Message / symptom

Likely cause

What to do

No GPS at all; settings show ⚠ … GPS_TYPE=0

Flight controller GPS type is not MAVLink

Set GPS1_TYPE (or GPS_TYPE) to 14 and reboot

No GPS at all; settings show ✓

The phone has no GPS fix (indoors)

Move the phone to open sky

PreArm: GPS 1: not healthy

GPS messages arrive too slowly or with gaps

Check the link between phone and flight controller

GPS 1: Bad fix then GPS 1: detected MAV

The GPS stream stopped for 4 seconds or more

Check the phone’s GPS fix and the flight controller connection

PreArm: Need Position Estimate or AHRS: waiting for home

EKF3 GPS checks fail — usually horizontal accuracy above 5 m

Compare the Status fields with the table above; see When the phone’s accuracy is not good enough

PreArm: Check mag field (xy diff …)

Compass disagrees with the field expected at the GPS location

Real vehicle: move the phone away from the compass and recalibrate; SITL: start SITL at the phone’s location

GPS Glitch or Compass error

The GPS position jumped more than its reported accuracy

Improve the sky view and keep the phone firmly mounted