Mapping Hacks

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Chapter 5, Mapping with Gadgets

#60 Improve the Accuracy of Your GPS with Differential GPS

HACK

directory and download and execute it. The file is a self-extracting ZIP

archive that will install the Jdgpsip application on your system. You’ll then

need to configure your GPS receiver to accept RTCM data at 4800 baud,

and, ideally, output NMEA data. This setting should be available in the

setup menu on your receiver, but check your owner’s manual for details.

Then connect your GPS to your computer via the serial cable provided by

your manufacturer. Make sure you know which serial port you’ve con-

nected it to—often COM1 or COM2.

You’ll want to try getting DGPS corrections somewhere where you can get a

reasonably clear view of the sky. Indoor GPS reception tends to be weak, at

best, due to the extremely low power of the satellite transmissions, so you

may want to go outside. A laptop with Wi-Fi makes this enormously easier.

Make sure your computer is connected to the Internet and your GPS receiver

is connected and powered on. Wait until your GPS gets a satellite lock. If it

doesn’t get a lock, you may need to find another location with a better view

of the sky. Note the accuracy that your GPS reports.

Getting Better Differentials

Now, start up dgpsip (or Jdgpsip). The dgpsip client should connect to dgps.

wsrcc.com on port 2101 by default. If you’re running the *NIX version of

dgpsip, you can start ...