So, on our side of things we have a guide https://docs.sparkfun.com/SparkFun_RTK_ … field-trip …I presume this is what you followed?
My main guess is that the ARP offsets need to be accounted for. Otherwise, there are several potential areas to investigate:
- Antenna Phase Center and Calibration
Antenna Phase Center Offset (PCO): Each antenna has a specific point where the signal is considered to be received, known as the phase center. This point can vary slightly based on the angle of the incoming signals. If your Trimble AG25 antenna is not calibrated or you don’t know its phase center offsets, this could introduce errors.
Antenna Calibration: Using a calibrated antenna with known offsets can improve accuracy. The National Geodetic Survey (NGS) provides calibration data for many antennas. If available, using this data in your processing software can help.
Antenna Height: Ensure you have accurately measured and entered the antenna height from the reference point (ground or another baseline) to the antenna phase center.
- Rinex File Processing
Correct Rinex Settings: Ensure that your Rinex files are correctly generated and contain all necessary information. Check that the correct antenna model and height are specified.
Processing Parameters: When submitting to CSRS-PPP, verify that all parameters, including the antenna type and height, are correctly entered. Any mismatch here can lead to positional errors.
- Environmental and Installation Factors
Multipath: Signals reflecting off nearby structures can cause errors. While your antenna has a clear sky view, reflections from the building or other objects might still affect the signal.
Interference: Ensure there are no sources of RF interference nearby that could affect the GPS signals.
- Equipment and Configuration
Receiver Settings: Double-check the configuration settings for both the F9P and Mosiac X5 boards. Ensure they are set up correctly for your application.
Firmware Updates: Make sure your GNSS boards and any associated software are up to date with the latest firmware. Manufacturers often release updates that improve accuracy and reliability.
- Comparison and Validation
Comparison with Known Points: Validate your RTK base station’s coordinates by comparing them with known survey points if available. This can help identify systematic errors.
Coordinate Systems: Ensure that all systems (RTK, PPP, RTX) are using the same coordinate system and datum. Mismatches here can introduce significant positional errors.
- Post-Processing
Verify with Multiple Services: If possible, try processing your Rinex files with other PPP services (like NRCan, OPUS, etc.) to see if the issue persists. This can help confirm if the problem is with the processing service or other factors.
While the lack of a calibrated antenna and unknown phase center can contribute to errors, the discrepancy you’re seeing (about 30 inches) suggests there might be multiple factors at play. Carefully reviewing and adjusting the above elements should help you identify and correct the source of the error.