>How to Obtain the Positioning Accuracy of an RTK GNSS Receiver<

Traditional GNSS software calculates the current position accuracy from the HDOP value in the NMEA message. This is suitable for non-RTK GNSS receivers, but this method does not apply to RTK GNSS receivers.

The positioning accuracy of an RTK GNSS receiver should be evaluated based on the following conditions:

  FIX Status (Float / Fix): "Fix" indicates a successful RTK high-precision solution.

  Baseline length between the receiver and the reference station.

  Number of satellites and signal strength.

  RMS accuracy.

For example:

The "4" in the green box indicates the current positioning mode is "RTK Fix," and we can assume the positioning accuracy is about 1 cm. Note that the HDOP value in the red box is still "0.4."

The HDOP value can be used as a reference, but it is not very meaningful for an RTK GNSS receiver. Even if the HDOP value is relatively large, as long as the communication between the reference station and mobile station is stable, and the solution status is "RTK Fix," the positioning accuracy can still remain within 1 cm.

To obtain the positioning accuracy of the P-70 Ultra, you can enable the HPPOSLLH (High Precision Geodetic Position Solution) message. This message includes the Horizontal Accuracy Estimate and Vertical Accuracy Estimate information at the end, which can be used to estimate the positioning accuracy.

Example with Windows:

Download and run "NavStarTool".

  Select the port where "Enhanced COM Port" is located, set the baud rate to "230400 bps," and click the connection icon. When you see data scrolling in the "NMEA" window, it means the connection is successful.

The port number in the screenshot may vary depending on your computer, for reference only.

Click "Receiver" — "Receiver Settings".

  Click "Read from Chip".

  Find "Receiver Parameters" - "Output POLARIS Message", and check the "HPPOSLLH" box.

  Click "Send to Chip" to save the settings. When you see the message "setting is done successfully", it means the modification has taken effect. Now, the HPPOSLLH message is enabled, and you can use it to estimate the positioning accuracy.

If your software cannot parse the HPPOSLLH message, you can use u-center to check the positioning accuracy.

Download and run "u-center".
　

Click the "Serial Port" icon and select the port where the P-70 Ultra is connected. Click the "Baud Rate" icon and select "230,400".

  Click "View" - "Message".

  Click "UBX" - “NAV” - "HPPOSLLH", and in the right window, you will see the real-time horizontal accuracy of 7 mm and vertical accuracy of 9 mm.