GPSLogger

GPS logger application for PPK (post process kinematics) for u-blox Neo M8P and Zed F9P GNSS units.

PPK provides centimeter-precision positioning using logs acquired from a GNSS unit and data form a nearby base station. The correction is not real time, but it doesn't need an internet connection, like RTK. For applications, like precise photo georeferencing this can be an optimal solution.

Typical application would be to connect a Raspberry Pi Zero W or similar to the GNSS unit for data acquisition.

Features

• Logging of RAW GPS data
• Web server for live monitoring
• Performing PPK correction on the recorded raw data

Prerequisites

• cmake
• QT5 (with QSerialPort and QWebSockets modules)
• (optional) Python3 for the provided utilities

Building and installation

mkdir build
cd build
cmake ..
make
sudo make install

For full functionality build the webserver and enable the provided systemd service.

PPK correction using RTKLIB command line utilities

The correction is made automatically using the provided correct.sh/correct.ps1 utility.

It needs the convbin and rnx2rtkp utilities from RTKLib in the current folder.

Useage (Linux/Mac):

./correct.sh [inputfile.ubx] [base.21o]

Useage (Windows PowerShell):

./correct.ps1 [inputfile.ubx] [base.21o]

The base station data ([base.21o] and [base.21n]) can be downloaded in France from the IGN France site.

Manual PPK correction

RAW to RINEX conversion:

convbin -r ubx -o [outfile.obs] [inputfile.ubx]

PPK correction:

rnx2rtk -k rtkpost.conf -o [outfile.pos] [rover.obs] [base.21o] [base.21n]

where rover.obs is the rover observation file obtained in the previous step; [base.21o] and [base21n] are the base station data (see above).

Applying the position data to another file containing timestamps

The gpssync_ui.py (with GUI - needs the Gooey library) or gpssync.py (command line) utility can create positional data in another CSV file containing timestamps. The utility might have to be updated for the structure of the CSV file.

Useage:

python3 gpssync_ui.py

or

python3 gpssync.py [--xarm xdist] [--yarm ydist ] [outfile.pos] [camerafile1.txt] [camerafile2.txt] ... 

where --xarm and --yarm define the lateral and axial distance between the GPS antenna and the camera.

The figure above shows the xarm and yarm parameters on a tractor. Note that yarm is positive in forward direction, xarm to the right.