GPS Measurement Tools

The GNSS Measurement Tools code is provided for you to:

• read data from GnssLogger App,
• compute and visualize pseudoranges,
• compute weighted least squares position and velocity,
• view and analyze carrier phase (if it is present in the log file).

Origin

This code is maintained on GitHub at the following link:

https://github.com/google/gps-measurement-tools

Matlab

Initial setup:

1. Extract the contents of the zip file to a directory, for example:

    ~/gpstools/*
   

   and include the directory ~/gpstools/opensource in your matlab path:

    addpath('~/gpstools/opensource');
   

   (Note: the tilde ~ is a place holder, don't actually use it, fill in the actual complete path)

2. Edit ProcessGnssMeasScript.m to add the demoFiles directory, as follows:

    dirName = '~/gpstools/opensource/demoFiles'
   

   (again, replace tilde ~ with actual complete path)

3. Run ProcessGnssMeasScript.m, it will run with pre-recorded log files.

To process a log file you collected from GnssLogger:

1. save the log file in a directory
2. edit ProcessGpsMeasScript.m, specify the file name and directory path
3. run ProcessGpsMeasScript.m

The code includes a function (GetNasaHourlyEphemeris.m) to read ephemeris files from the NASA's archive of Space Geodesy Data, ftp://cddis.gsfc.nasa.gov It will automatically go to the ftp when you have a new log file. On some systems you need to use passive mode FTP; if this is required, see The Mathworks site for how to do it. Or (simpler): get the appropriate ephemeris file 'by hand' from the Nasa ftp site (GetNasaHourlyEphemeris.m will tell you the correct url and filename), copy the file to the directory where your log file is, and GetNasaHourlyEphemeris.m will read it from there.

To evaluate an NMEA file against another NMEA file:

Use Nmea2RtkMetrics.m to compute position accuracy metrics from two NMEA files:

    dir='./NmeaUtils/example/';
    refFileName='MTV.Local1.SPAN.20200206-181434.gga';
    testFileName='MTV.Local1.ublox-F9K.20200206-181434.nmea';
    Nmea2RtkMetrics(testFileName,refFileName,dir)

This will lead to the following output:

    50% (m), 95% (m), TT1M (s), TA1M (s), AA5S (m), AA10S (m), XTrack 50% (m), XTrack 95% (m)
    0.49, 0.81, 0, 0.91, 786.00, 0.91, 0.09, 0.27

Use Nmea2ErrorPlot.m to generate CDF of horizontal error:

    Nmea2ErrorPlot(testFileName,refFileName,dir)

For a summary of the open source GNSS Measurements Tools

See ~/gpstools/opensource/Contents.m or type 'help opensource' in matlab command window.

Platform specific notes:

For Windows: use \ (backslash), instead of / for directories.

For Mac: when installing MATLAB. System Preferences --> Security & Privacy --> Allow Apps to be downloaded from: Mac App Store and identified developers

Uncompress/Unzip utility called from GetNasaHourlyEphemeris.m: The ephemeris on the Nasa ftp is Unix-compressed. GetNasaHourlyEphemeris will automatically uncompress it, if you have the right uncompress function on your computer. If you need to install an unzip utility, see http://www.gzip.org/ Then search for uncompress in the GetNasaHourlyEphemeris function to find and edit the name of the unzip utility:

unzipCommand='uncompress';%edit if your platform uses something different 

If you uncompress the file 'by hand' and rerun GetNasaHourlyEphemeris.m, it will read the uncompressed file.

GNSSLogger

Sample App that allows registering for various Android location related measurements, log the measurements to the screen and optionally to a text file and as well analyze these measurements.

Version 2.0.0.0 of the GnssLogger is enhanced with the following features:

1. Compatible with Android-O new features like AGC and multi-frequency support
2. Includes weighted least square position and velocity computations
3. Includes weighted least square position and velocity uncertainty computations
4. Compares the computed weighted least squares from raw GPS measurements vs the Kalman Filter position provided by the GPS chipset.
5. Shows the computed weighted least square position from raw GPS measurements on Google Maps vs the Fused Location Provider reported position.
6. Has an A-GPS control tab that allows clearing and injecting assistance data
7. Plots CN0 of visible satellites and as well prints the top 4 visible satellites CN0 and average values
8. Performs and plots residual analysis for both pseudorange residuals and pseudorange rate residuals
9. Enhanced Logging both to screen and to files functionalities.

This source code is supplied as an Android Studio project that can be built and run with Android Studio.

The APK is also provided for convenience.

For information about the data logged to files see LOGGING_FORMAT.md.

Pseudorange Library

Position Solution Engine from Gnss Raw measurements as a dependency android library of GnssLogger application. Part of the dependencies concerning communicating with SUPL server to retrieve ephemeris info has been packed in Jar for project cleanness. To access the SUPL server related code, please visit git repository of Android CTS. https://android.googlesource.com/platform/cts/+/master/tests/tests/location/src/android/location/cts

Copyright Notice

Copyright 2016 Google Inc.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.