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  GT32 resources

  Setting up Navi GT31


GT32 resource website                                      by Tom Chalko

GT32-50 is a new instrument that combines GPS-Doppler with inertial navigation technology and magnetometer to enhance measurement of motion. GT32 contains two GPS-Doppler engines and 3-axis alias-free DC accelerometer sampling at 50Hz (providing 150 acceleration samples per second), all logging to SD card in compact binary format.

GT32 has evolved from GT31 and can be described as "9 instruments in one", all fitting into a single GT31 case and sharing one SD card. In essence, an additional hardware module has been fitted inside GT31 to extend its capabilities. This extra module comprises an autonomous gps-Doppler engine, three DC accelerometers 3D magnetic compass and a thermometer.


is aimed for people who want to measure jumps and acrobatics or carry multiple GT31 units in their effort to improve motion measurement accuracy. GT32 is cheaper and more compact than two GT31 instruments. In addition, GT32 offers possibilities that are beyond reach of a pair of GT31 units, such as higher bandwidth and detection of angular orientation (yaw, pitch, roll angles) of a moving craft, or in sport for example.

This website contains links to technical, theoretical, scientific and software resources to assist GT32 users to make the most of their GT32 instrument.
GT32-50 potential

Using new GT32 50Hz instrument offers many interesting possibilities in sport and other activities:

  • it can measure 3D speed simultaneously using 3 independent ways (2*GT31 GPS-Doppler and 1 integration of accelerations)
  • it can measure jumps and acrobatic maneouvres in many sports (windsurfing, kitesurfing etc..)
  • can increase the bandwidth of motion measurements beyond limits of the GPS technology alone
  • less bulk to carry than two separate GT31 instruments
  • Potential for detection, verification and correction of gps-Doppler aliasing problems (during sailing and speed record attempts for example)
  • No kinematic differences between two internal GT31 gps-engines, because they share the same GPS antenna. This improves repeatability and reproducibility of speed measurement, reduces error margins in speed measurement and enables calibration of gps-Doppler engine performance
  • Potential to measure motion parameters (such as speed for example) 50 times per second, because integrated and aligned accelerations can be used to fill-in gaps between 1Hz GPS-Doppler speed data.
  • potential to measure the angular orientation of craft in motion (yaw, pitch and roll angles)

Some of the above potential can be used today using the existing GPS software tools, some require development of new tools. My view is that progress cannot really be stopped, so it is better to support it.

GT32-50 firmware
For latest GT32 firmware please see GT31 firmware update page.
GT32 output file

GT32 generates a single "extended SBN" file that contains GPS data from 2 independent GT31 chipsets plus 3 sets of 50Hz acceleration data (150 acceleration samples per second) and temperature readings.

Before standard GPS-data processing software is improved to access the second gps-engine data inside "extended SBN file" I provide a simple software utility to extract "internal gps-engine" data into a separate SBP file.

Downoad GETSBP utility, unzip it, and provide a shortcut to it on your desktop. Then drag-and-drop GT32-generated SBN file to this shortcut. GETSBP will generate SBP file in the same folder as the original SBN file. This extracted SBP file will have name similar to source SBN, but will end with "-a.SBP"

Both SBN and extracted SBP file can be viewed and processed using standard GPS data processing software.

Software developers: please contact me for details of SBP, acceleration and temperature records in "extended SBN" file.

GT31 Settings

There are 2 methods of setting-up Settings in GT32

  • manual: using buttons in GT32 itself. Setting up process is essentially the same as for GT31, with some extra steps: setting D0,D1,D2,D5 =ON and D3,D4 =OFF in MISC menu.
  • using NavilinkII : this method enables you to backup/share/restore complete set of GT31 settings. Download my GT32 settings file and use NavilinkII>Settings>Write function to load this setting file to your GT32. Please check if D0,D1,D2,D5 =ON and D3,D4 =OFF in MISC menu. You may wish to change the "time zone" in Settings as well.
GT32 software
  • GETSBP : software to extract SBP data from "extended SBN" file generated by GT32. Please see the GT32 output file section above for details
  • ACC-CAL: software for calibrating 3 accelerometers inside GT32. Scale factors and zero-acceleration offsets are determined for each accelerometer on a basis of a simple 1-minute static experiment. Please see readme.txt file for details of the calibration procedure. Accurate calibration is very important for correct implementation of acceleration measurements in inertial navigation.
  • FOURIER: This program demonstrates Fourier series reconstruction of a continuous process from alias-free discrete series of samples. The process is "gps speed sailing" and hence Fourier program is well suited to analyze your speed sailing data.

    Specifically, Fourier program can be used to analyze "Speed Record" attempts monitored by GT32 or a pair of GT31s. Pease try using Fourier program to process your current SBP and SBN (speed sailing) files.

    When you load 2 synchroneous SBP files, or "exended SBN" file from GT32, the Fourier program can create REPORT outlining the details of "claimed speed" computation that is used for Speed Records. Please see "Theory and publications" section below for technical details.

    Fourier program currently supports
    •   single SBP and SBN files
    •   2 synchroneous files (SBP and/or SBN)
    •   "extended SBN" files generated by GT32
    •   Google Earth direct interface to view your speed attempts (Google Earth must be installed on your computer)

    In the not-too-distant future Fourier program will demonstrate combining gps-Doppler and inertial navigation (acceleration) data captured by GT32.

Theory and publications

[1] T.J.Chalko, Reconstructing data from alias-free discrete series of samples, NU Journal of Discovery 2009,

[2] T.J.Chalko, Combining accelerations and GPS-Doppler velocities, NU Journal of Discovery (draft 2010)

[3] T.J.Chalko, Estimating Accuracy of GPS Doppler Speed Measurement using Speed Dilution of Precision (SDOP) parameter, NU Journal of Discovery 2009,