Mapping Hacks

Improve the Accuracy of Your GPS with Differential GPS #60

Chapter 5, Mapping with Gadgets

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HACK

into a TCP/IP packet, and sends it back out. The correction data is in

RTCM SC-104 format, a protocol published by an industry group called the

Radio Technical Commission for Maritime Services. Most consumer GPS

equipment can be configured to accept RTCM DGPS corrections, so all a

DGPS-over-IP client needs to do is assemble the SC-104 data on the receiv-

ing end and pipe it out to the GPS receiver over a serial port. The net effect

of DGPS-over-IP is, in essence, to treat the Internet as an indefinitely long

RS-232 extension cable!

Setting Up DGPS-over-IP on Linux

In order to use DGPS-over-IP, you’ll need to get a suitable client. If you’re

running Debian Linux, you can simply run

apt-get install dgpsip. If you’re

running a different *NIX, you can get the latest source code tarball from

http://www.wsrcc.com/wolfgang/ftp/. The file should be called dgpsip-

x.xx.

tar.gz, where x.xx is the latest version (1.33, as of this writing). You can

build and install it as follows:

$ tar xvfz dgpsip-x.xx.tar.gz

$ cd dgpsip-x.xx

$ ./configure

$ make

Then, as root, run:

$ make install

Next, you may want to symlink your serial port (usually, /dev/ttyS0 for the

first serial port, but it might be /dev/ttyS1)to/dev/gps, so that dgpsip knows

by default where to look:

$ ln -s ttyS0 /dev/gps

Finally, check your /etc/services file ...