Linux.Desktop.Hacks [Electronic resources] نسخه متنی

Hack 67. Map Your Meatspace

A bird's-eye view of the world
on your Linux desktop.

When Global Positioning System (GPS) technology was launched, it was
heralded as the next big thing. Although its usefulness has
not been quite as explosive in the consumer market as many people
predicted it would be, GPS has proved useful in areas, such as
satellite navigation systems and mapping tools. Although many people
think only ramblers and walkers use GPS, the technology actually is
useful in numerous applications, many of which you can perform from
your Linux desktop. This hack shows you how you can hook up a GPS
unit to your Linux desktop and use some open source tools to help map
out your area.

8.14.1. Connect the GPS to Linux

A number of GPS units are compatible
with Linux, and all of them come with either serial or USB
connections. Although two types of connections are available, the USB
connector simply uses a special chip called the FTDI chip to convert
a legacy serial connector to a USB connector. This chip requires a
special driver to convert from a USB to a serial port. A Linux driver
has been developed for this and it is available at http://ftdi-usb-sio.sourceforge.net/.

Each connector is compatible with Linux, and most of the USB GPS
units include the FTDI driver in the kernel. If you are using one of
these USB devices, you need to ensure that you have USB drivers
compiled into the kernel. You should ensure you have the UHCI, UHCI
Alternate Driver, or OHCI options from the USB Support page in the
kernel configuration tool. Which option you choose depends on your
motherboard; consult your motherboard's manual for
information on this.

When you have installed the USB or serial drivers and you have
plugged in the device, the GPS unit should be available on the system
in /dev/ttyS[n] for a serial GPS or
/dev/ttyUSB[n] for the USB equivalent. Now you
can look in /dev to see the name of the port
from which you can access the GPS:

foo@bar:~$ ls -al /dev/ttyS*

Or, if you have a USB device:

foo@bar:~$ ls -al /dev/ttyUSB*

At this point your GPS is recognized by the system, and you can
configure your GPS applications to look at this port for your GPS
unit. If you are thinking of purchasing a GPS unit, it is recommended
that you get one with full NMEA compatibility. This will ensure that
the unit will work with most of the common GPS software tools.

8.14.2. Use Mapping Software

You probably want to use GPS so that you can view a map of
your area as you travel through it. Some GPSes display a general map
with streets and street names, and other maps go one step further to
provide instructions on where to go (such as "at the
end of the road, turn left" instructions). The
former system uses general mapping information and the latter is a
vector-based satellite navigation system.

For general mapping information, a useful tool is GpsDrive
(http://gpsdrive.kraftvoll.at/).
You can use this application to indicate your current location, to
plot waypoints (locations in latitude and longitude), and to interact
with other GPS users over a wireless network.

Although GpsDrive is a
useful tool, one of
its problems is that free maps of Europe and many other parts of the
world are not available for use with it. The lack of free maps is a
big problem with GPS software in general. GpsDrive does spider some
online mapping web sites to download maps for the areas you are in,
but that is useful only when a map is available, and only if you have
wireless connectivity when you enter a new area. To solve this
problem, you need to use a script that can download maps of entire
areas in advance of your visit (this script is covered later in this
hack).

Another option, particularly if you just want to see where your
location is in the world, is to use the free NASA maps to plot your
position inside GpsDrive. Before you do this, you should ensure you
have at least 3GB of disk space available, as the NASA maps are huge.
You need to download two maps from map" in the "Show map
type" field.

8.14.3. Spidering Mapping Information

Although GpsDrive allows you to download maps displaying the area you
are in, it is likely that you will want to download a number of maps
displaying different parts of your area or country. You can do this
with a small shell script called gpsfetchmap.pl,
which is included with GpsDrive. You can use this script to spider a
number of maps between two sets of longitude and latitude points and
download all the content for use with GpsDrive. All these maps will
be downloaded from the Expedia Germany web site (http://www.expedia.de/).

To use the script, you need to pass it the latitude and longitude of
the top left corner and bottom right corner of the region you want
maps for. The top left corner is referred to as the starting
latitude/longitude, and the bottom right corner is the ending
latitude/longitude. You should also pass the script the scale of the
map. For street-level detail, a scale of 1500 is recommended. Here is
an example of the command in use:

foo@bar:~$ gpsfetchmap107.pl --start-lat 52.2401 --end-lat 
52.3096 --start-lon 13.2265 --end-lon 13.3203 -sc 1500 -a 4 -p