I have some experience with this, and what you are asking is not quite so
simple. I will try to break it down into general categories:
1. How to obtain your position via GPS?
There are a number of readily available GPS receivers out there that all
you need to to do is provide power and they start spitting out their
position. When searching try to find one that has RS232 or USB output,
these are the easiest to deal with. The data is basically an ASCII text
record that can be easily parsed into lat/long data.
2. What do you want to do with the data once you have it?
If you just want to store it to a file on the truck and retrieve it later
to see where the truck as been all day that's easy, just write the GPS
data to a file.
If you want to display it in the truck, e.g. on a map, then you need some
software to draw the map. There are several API kits available if you
want to roll your own, and the map data is also available from several
sources.
If this is all you want to then you can save yourself a LOT of trouble an
just buy a package. That includes the receiver and software for a
laptop, Win CE device or Palm device. There are several stand alone
units too that provide a complete package you just plug into your
lighter.
If you want "dispatch" to know where the truck is, then you have to
transmit the position from the truck. This can be done by various radio
modems and a second data channel on your radio system. Another option is
one of these cellular data cards that basically give you a mobile
wireless Internet connection.
Here again, there are several services that provide a black box and
software and/or services with all of the details worked out. The prices
vary but typically it cost about $500-$600 per truck for the black boxes,
and $50 per month per truck for the service. Dispatch just points to a
web page and can track the truck.
Some cellular services are even providing this type of service with GPS
enabled phones.
The bottom line is that there are several established products that are
fairly good. They aren't cheap and may not do exactly what you want or
work exactly the way you want, but it is a lot of work to roll your own
to make "exactly" what you want. For 6 trucks I am not sure it is cost
effective.
I did it for a company with 35 trucks and with more than a year worth of
development (hardware and software) I am not sure it was cost effective.
I mean it does exactly what we want and works great, but I don't think we
saved any money when you consider my time, and we could probably have
lived with some of the deficiencies for the canned packages...
I am not trying to discourage you, but do your research and put some
number down on paper.
It was a very interesting project.
