RTK Express Base & Rover Relative Position Measurement Questions

GPS/GNSS Development Boards
1

I want to measure the relative positions of two RTK express antennas in ECEF (or NED). I’m trying to confirm this product (https://www.sparkfun.com/products/18442) will do what I want.

I have 2 areas of questions – hardware configuration and data logging.

Hardware Config: Regarding connecting the receivers, what’s the difference of blue tooth versus radio?

  • Under Bluetooth, how far apart can the receivers be?

  • What app is needed on a phone to connect over Bluetooth?

    • Data Logging: Is there any way to directly log the relative position of the RTK express antennas (base and rover) in ECEF? Or do you have to log each one as an absolute position, and difference those in post processing?

    I found that u-blox can log the relative position in NED. That would do for me as well as ECEF. Will the Rover be able to log this?

    https://docs.sparkfun.com/SparkFun_RTK_ … l-messages

  • NAV-RELPOSNED

    • <LINK_TEXT text="https://github.com/commschamp/cc.ublox. … ed.h#L782
    ">cc.ublox.generated/include/cc_ublox/message/NavRelposned.h at master · commschamp/cc.ublox.generated · GitHub
    </LINK_TEXT>

    2

    roman.luz:

  • What app is needed on a phone to connect over Bluetooth?

    • Here it says “he built-in Bluetooth® connection via an ESP32 WROOM enables the user to use the RTK Express with their choice of GIS application on a phone or tablet.”

    https://github.com/sparkfun/SparkFun_RTK_Express

    3

    The RTK product line is very capable of what you describe. Logging the NAV-RELPOSNED is very straight forward and can be enabled on the Rover for post analysis.

    what’s the difference of blue tooth versus radio?

    I don’t understand the question. Bluetooth is what transfers NMEA data from the RTK unit to your phone. Most users use a phone or surveying computer for what’s called Data Collection. It’s like a mini-PC hardened for field work, that runs a specific GIS app. Some folks use very expensive packages that have lots of tools built in. I recommend SW Maps because it’s great for simple work, it’s free, and runs well on Android phones.

    To connect the Base to the Rover, you need a radio link to transmit corrections from Base to Rover. RTCM corrections transmitted between RTK units over Bluetooth is not supported at this time. Generally, the link between units is done over WiFi. Many surveyors use cellular hot-spots to get the Base onto WiFi, that is then on the internet. At the Rover, you then obtain the corrections over cellular using your phone (read about NTRIP clients).

    Under Bluetooth, how far apart can the receivers be?

    RTCM corrections transmitted between RTK units over Bluetooth is not supported at this time. For connecting a phone to the RTK unit, we’ve transmitted over 50m.

    What app is needed on a phone to connect over Bluetooth?

    For data collection from the RTK Rover, we recommend SW Maps for beginners: https://docs.sparkfun.com/SparkFun_RTK_ … e/#sw-maps but there are more listed there.

    Is there any way to directly log the relative position of the RTK express antennas (base and rover) in ECEF? Or do you have to log each one as an absolute position, and difference those in post processing?

    Yes, the RTK unit is capable of logging ECEF. The log on the Rover will contain coordinates for the Rover. These coordinates will be relatively accurate to the Base. Said differently, if the Base is 1 meter off, all Rover coordinates will be 1 meter off, but will be within ~14mm accuracy of all points measured. This is great for measuring the shape and lengths of things in the field, extremely accurately. If you need absolute accuracy, look at a permanent base or getting corrections from a NTRIP service.