The Area Measure app can use an external GNSS receiver instead of the phone's own GPS. With an RTK receiver, a correction service and internet on the phone, points can be measured to the centimeter: see What you need for centimeter accuracy.
What you need
- A receiver that sends standard NMEA 0183 position data: GGA at the least. GST, GSA and GSV add the accuracy estimate and satellite details.
- A Bluetooth LE connection, or a Wi-Fi (TCP) connection to the receiver or its hotspot. Receivers that only offer classic Bluetooth (SPP) can't be used: iPhones and iPads cannot connect to them, and the app uses the same two connections on Android. See Choosing a GNSS receiver.
Connect over Bluetooth
- Turn the receiver on and keep it close to the phone.
- In the app, open Settings → External GNSS / NTRIP.
- Set Connection to Bluetooth, then tap Choose a receiver.
- Tap your receiver in the list. The app keeps it as My receiver.
- Tap Connect.
If the receiver is not listed, check that Bluetooth is on, that the app is allowed to use it, and that the receiver is discoverable. Not every nearby Bluetooth device is a GNSS receiver.
Connect over Wi-Fi (TCP)
- Join the receiver's Wi-Fi network, or put the phone and the receiver on the same network.
- In Settings → External GNSS / NTRIP, set Connection to TCP.
- Enter the receiver's Host / IP and Port (its NMEA output port, from the receiver's manual), then tap Connect.
On Android
The receiver settings are a panel in Settings: tap External GNSS / NTRIP to open it. Turn on External receiver, choose BLE or TCP, and then:
- BLE: tap Scan BLE devices, then tap your receiver's name.
- TCP: enter the Host / IP and Port.
Tap Connect / apply. The first time, allow Bluetooth access and notifications: the notification keeps the connection running and has a Disconnect button.
Check that it works
Once data arrives, the map shows Using receiver location with the fix level and the receiver's accuracy estimate, for example Centimeter-level (RTK fixed) · ±0.011 m. The receiver page shows the same under Position, and Technical details shows the satellites, their signal strength and the receiver's error estimates.
- Could not connect: the app gives up after 10 seconds without data. Check that the receiver is on, in range, and sending NMEA.
- Connected · waiting for a current position: data is arriving, but the receiver has no position yet. Take it outdoors with a clear view of the sky.
- Phone time doesn't match the receiver: turn on automatic date and time on the phone.
While you measure
Walking a boundary, capturing corners and recording a route all use the receiver while it is connected. If the receiver goes out of range, the app tells you: depending on the measurement, it either carries on with the phone's GPS until that measurement ends, or waits for you to bring the receiver back. Keep the phone within a few meters of a Bluetooth receiver; below about −85 dBm the link may drop.
Closing the app disconnects the receiver. Connect it again the next time you open the app.
Photos taken in the app use the receiver's position while it has a current fix. If the receiver stays on a tripod while you take photos elsewhere, set Photo location to Phone GPS.
For centimeter accuracy the receiver also needs RTK corrections: see Set up RTK corrections (NTRIP).