A free app that supports external RTK GNSS receivers
The receiver supplies the centimetre; the app's job is to read it correctly and record it correctly.
Field takeaways
- The external receiver computes the position.
- Standard NMEA works with most brands.
- NTRIP corrections are configured separately.
- Antenna height goes in before the first point.
- A known-point check validates the chain.
What being free does not change
The accuracy chain is receiver, correction stream and check. The app is one link in it: it reads the data, shows the accuracy indicator and records the result. A paid app does not deliver the centimetre, and a free one does not take it away.
How the connection is made
First pairing in the phone's Bluetooth settings, then selecting the receiver in the app as the coordinate source. The second step is the one most often skipped, and when it is, the app quietly keeps using the phone's own GPS.
Which receivers work
Receivers that broadcast standard NMEA over Bluetooth. MapLab Survey has been tested with Emlid Reach, SparkFun RTK and many u-blox-based models. Because the protocol is standard, devices outside that list are likely to work too, but confirm with your own hardware.
Corrections are a separate channel
Bluetooth connects the phone to the receiver, while corrections arrive from an NTRIP network. Address, port, mountpoint and credentials are configured separately; when the link drops in the field, the age of the corrections is the first thing to check.
Two things before the first point
Enter the antenna height and measure a known point. A forgotten antenna height is the most common cause of a systematic error across the whole day's work, and it cannot be corrected afterwards.
Try these steps on your own phone.
MapLab Survey handles RTK/GNSS point capture, drawing, area and volume calculations and coordinate conversion, then exports to DXF, KML/KMZ, GeoJSON, Shapefile, GeoPackage, NCZ or CSV. Capture, calculation and export work offline. Live NTRIP corrections and online basemaps need a connection.
Frequently asked questions
Is RTK support behind the paid tier?
External receiver connection is available in the free version.
Which protocol is used?
Standard NMEA over Bluetooth.
Does it work on iPhone?
Yes, the platform makes no difference; the receiver does.
Is internet required for NTRIP?
For the corrections yes; for the receiver itself no.
Technical references
The field guidance in this article is aligned with the technical and official references below.
Related: The limit of phone surveying · Bluetooth RTK GNSS · RTK GNSS field accuracy · MapLab Survey