SparkFun RTK Surveyor Hookup Guide
Bluetooth and NTRIP
The RTK Surveyor transmits full NMEA sentences over Bluetooth serial port profile (SPP) at 4Hz and 115200bps. This means that nearly any GIS application that can receive NMEA data over serial port (almost all do) can be used with the RTK Surveyor. As long as your device can open a serial port over Bluetooth (also known as SPP) your device can retrieve industry standard NMEA positional data. The following steps show how to use SW Maps but the same steps can be followed to connect any serial port based GIS application.
The best mobile app that we’ve found is the powerful, free, and easy to use SW Maps by Softwel. You’ll need an Android phone or tablet with Bluetooth. What makes SW Maps truly powerful is its built-in NTRIP client. This is a fancy way of saying that we’ll be showing you how to get RTCM correction data over the cellular network. If you’re using a serial radio for your correction data, you can skip this part.
When powered on, the RTK Surveyor will broadcast itself as either 'Surveyor Rover-BC41' or 'Surveyor Base-BC41' depending on the position of the SETUP switch. Discover and pair with this device from your phone or tablet. Once paired, open SW Maps.
From SW Map's main menu, select Bluetooth GNSS. This will display a list of available Bluetooth devices. Select the Rover or Base you just paired with. Select 'u-blox RTK' (rather than just 'u-blox') from the Instrument Model dropdown. This is important and will enable the use of NTRIP. If your are taking height measurements (altitude) in addition to position (lat/long) be sure to enter the height of your antenna off the ground including any ARP offsets of your antenna (should be printed on the side).
Click on 'CONNECT' to open a Bluetooth connection. Assuming this process takes a few seconds, you should immediately have a location fix.
Next we need to send RTCM correction data from the phone back to the RTK Surveyor so that it can improve its fix accuracy. This is the amazing power of RTK Surveyor and SW Maps. Your phone can be the radio link! From the main SW Maps menu select NTRIP Client. Not there? Be sure to select 'u-blox RTK' instrument when connecting. Disconnect and change the instrument choice to enable the NTRIP Connection option.
Enter your NTRIP caster credentials and click connect. You will see bytes begin to transfer from your phone to the RTK Surveyor. Within a few seconds the RTK Surveyor will go from ~300mm accuracy to 14mm. Pretty nifty, no?
What's an NTRIP caster? In a nut shell it's a server that is sending out correction data every second. There are thousands of sites around the globe that calculate the perturbations in the ionosphere and troposphere that decrease the accuracy of GNSS accuracy. Once the inaccuracies are known, correction values are encoded into data packets in the RTCM format. You, the user, don't need to know how to decode or deal with RTCM, you simply need to get RTCM from a source within 10km of your location into the RTK Surveyor. The NTRIP client logs into the server (also known as the NTRIP caster) and grabs that data, every second, and sends it over Bluetooth to the RTK Surveyor.
Don't have access to an NTRIP caster? We have a tutorial for that! Checkout How to Build a DIY GNSS Reference Station. Remember, you can always use a 2nd RTK Surveyor in Base mode to provide RTCM correction data but it will less accurate than a fixed position caster.
Once you have a full RTK fix you'll notice the location bubble in SW Maps turns to green. Just for fun, rock your rover monopole back and forth on a fixed point. You'll see your location accurately reflected in SW Maps. Millimeter location precision is a truly staggering thing.