Data Hacking

218 Part III — Data Hacking
7. To record the input, click the Record button. This brings up a dialog box asking you to
choose a location in which to save the NMEA output file.
8. To stop recording, click Stop.
9. Once you are done, you can examine the NMEA output file. A sample is shown in
Figure 9-19.
FIGURE 9-19: Sample NMEA output
NMEA output files are plaintext files that can be processed by a variety of GPS applications.
For example, you can import a file into an application such as Memory Map and
have the NMEA data translated into a route that appears on the map as an overlay.
However, unlike a real-time signal from a GPS, the file can be replayed without requiring
a clear view of the sky.
In theory, this enables you to separate the tracking and mapping elements of recording the
data. This would enable you to create a simple yet effective tracking system (for, say, a car).
All you need is a GPS and a Pocket PC device running GpsGate.
Connect the GPS to the Pocket PC and set up GpsGate to log the NMEA (the software is the
same as the Windows version). This will create a log file that you can later examine. Because
each NMEA sentence contains a checksum, tampering with the actual log is unlikely (hide the
system well and no one need know it was fitted to the vehicle!).