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Raw GNSS Measurements

The Android Framework provides access to raw GNSS measurements on several Android devices.

You can find the tools in the GPS Measurement Tools repo on GitHub, which includes the GNSS Logger APK, the GNSS Analysis app for Linux, Windows, macOS, and the Installation and User Manual.

Original equipment manufacturers (OEMs), developers, and researchers can make use of the tools in this page to test new phone designs, validate functionality, develop new algorithms, evaluate improvements to the GNSS system implementation as well as building value added apps.

SUPL Client Sample Code

Suplclient is sample code that accesses to obtain real time ephemeris. The SuplTester class provides an example on how to use the SUPL Client Project. The SuplTester sets up the SUPL TCP connection specifications, then at a given latitude and longitude sends an LPP SUPL request and prints the SUPL server response.

Antenna calibration information

Starting in Android 11 (API level 30), you can use the GnssAntennaInfo class to access antenna characteristics, such as: phase center offset (PCO) coordinates, phase center variation (PCV) corrections, and signal gain corrections. These corrections can be applied to the raw measurements to improve accuracy.

When using GnssAntennaInfo, keep the following system behaviors in mind. They are designed to enhance user privacy.

  • The characteristics supplied by this API are only specific to the device model, not an individual device.
  • Use of the GnssAntennaInfo class requires the ACCESS_FINE_LOCATION permission.

Logging raw measurements

You can use Android Studio to build an app that captures raw GNSS measurements and logs them to a file. The GPS Measurement Tools project includes GNSS Logger, a sample app that shows how to log data related to Android location, including raw GNSS measurements.

Download the GNSS Logger APK to install the sample app in your device.

To get GNSS output with the sample app, your device must support raw GNSS measurements.

Once you have captured the GNSS log using the GNSS Logger, you can copy the log files from the device to your computer for further analysis. From within the GNSS Logger you can send the files to yourself via email or save them to Google Drive. Alternatively, you can save the files using the file management app on the device, or you can use the Android Debug Bridge (ADB) as explained in Copy files to/from a device.

To browse the sample source code, see the GNSSLogger folder in the GPS Measurement Tools repository on GitHub.

Analyzing raw measurements

The GNSS Analysis app reads the GPS/GNSS raw measurements collected by the GNSS Logger and uses them to analyze the GNSS receiver behavior, as shown in figure 1.

You can download the app for Linux Windows, and macOS systems, or download the Installation and User Manual.

GNSS Logger and GNSS Analysis

Figure 1. GNSS Logger collects the measurements that can be consumed by GNSS Analysis.

The GNSS Analysis app is built on MATLAB, but you don't need to have MATLAB to run it. The app is compiled into an executable that installs a copy of the MATLAB Runtime.

GNSS Analysis Control Panel

The GNSS Analysis control panel, shown in figure 2, lets you manage app features, such as:

  • Select which satellites are displayed.
  • Control the reference position, velocity, and time (PVT) used for calculating measurement errors.
  • Generate analysis reports.
  • Define a window in the data between start and end times.

GNSS Analysis Control Panel)

Figure 2. GNSS Analysis control panel

GNSS Analysis interactive plots

The GNSS Analysis app provides interactive plots organized in radio frequency (RF), clocks, and measurements columns, as shown in figure 3.

GNSS Analysis interactive plots)

Figure 3. GNSS Analysis app displaying interactive plots.

The RF column shows the following data:

  • For each constellation, the four satellites with the strongest signals.
  • For each satellite, the time plot of carrier to noise density (C/No).
  • The skyplot of satellite positions.

The clock column shows the following data:

  • The pseudoranges.
  • The offset frequency of the receiver clock, which is computed using one of the following reference positions:

    • Automatically computed mean position.
    • Latitude, longitude, and altitude entered by the user.
    • National Marine Electronics Association (NMEA) file with truth reference PVT.
  • The offset of the standby clock that keeps time when the receiver resets the duty cycle of the primary oscillator.

The measurements column shows the following data:

  • The weighted least squares position results obtained from the raw pseudoranges. The weighting is done using the reported uncertainty of each measurement, which is part of the raw measurement API spec.
  • The errors of each pseudorange for each measurement.
  • The errors of each pseudorange rate for each measurement.

GNSS Analysis test report

GNSS Analysis can generate a test report, as shown in figure 4, that evaluates the API implementation, received signal, clock behavior, and measurement accuracy. For each case, the app reports whether the receiver passed or failed the test based on the performance measured against known benchmarks. The test report is useful for device manufacturers, who can use it as they iterate through the design and implementation of new devices. To generate the test report, click Make Report.

GNSS Analysis test report

Figure 4. GNSS Analysis test report

The Compare tab provides a side-by-side comparison, shown in figure 5, of C/No from several GNSS log files, which is useful when comparing the RF performance of several devices.

C/No data comparison side-by-side

Figure 5. Side-by-side comparison of C/No data from several log files

Interested in the source code? The GPS Measurement Tool Project provides an open source MATLAB example that you can use to perform the following actions using GPS constellation signals:

  • Read data captured with the GNSS Logger sample app.
  • Compute and visualize pseudoranges.
  • Compute weighted least squares position and velocity.
  • View and analyze carrier phase.

GNSS Analysis app v3.0.3.0 release notes

GNSS Analysis app version includes the following updates:

  • Adds Plots:
    • Kalman Filter position from WLS PVT
    • WLS relative position from ADR (Carrier Phase)
    • ADR (Carrier Phase) Single Difference Residual
  • Adds Refresh Positions to regenerate position plots based on selected satellites.
  • Adds Elevation Mask control.
  • Optimized downloading of ephemeris files, uses native unzip inside Matlab runtime for all BKG *.gz ZIP files.
  • Adds Device Position as an option for Reference PVT.
  • Adds CustomDataFilter.m capability, filtering on any of the # Raw header values.

Provide feedback

We want to improve the support for GNSS on Android. Let us know about any issues with GNSS support on Android by using the GNSS issue tracker. Please check if your issue has already been addressed in the FAQ before posting it.

If you have used the GNSS Analysis tools, please provide feedback by answering a short survey. If you have other questions or a request for support, see Developer Support Resources.

You can find answers to frequently asked questions in the GNSS Analysis Tools FAQs.