to Evaluate GPS Solutions for Your PDA Posted August 2003 by Tong
Zhang, Senior Editor
With more and more GPS packages coming out for the
PDAs, PDA users can enjoy a selection of products from which they
can pick the best to suite their needs. But what process does one
go through, especially for a user who is new to the GPS solutions
on PDA, to pick the best package? Here is a short guide to put you
on the right track. To learn more about GPS, read our GPS FAQ.
There are generally three major components in
a GPS solution that you should evaluate: the GPS receiver, navigation
software and map data. We will go over each aspect and give you
some advice on how to do the evaluation.
Often GPS solution vendors re-brand GPS receivers from
OEMs (original equipment manufacturers). Almost all the current new
GPS receivers are 12-channel parallel receivers. A12-channel parallel
receiver can track up to 12 GPS satellites and it tracks them with
dedicated hardware for each satellite, which leads to a faster fix.
In theory, you only need 4 satellites to have a 3D fix. Currently
there are no more than 11 GPS satellites (space vehicles) in our
hemisphere, and it’s not unusual if you have only 5-6 satellites
in view. So the 12 channel GPS has more than enough separate hardware
to track each satellite in sight.
Having 12 channels in your GPS makes the calculation
faster, but not necessarily more accurate. No GPS is 100% accurate.
You can read our GPS FAQ to learn what affects GPS accuracy. Essentially
you can get anywhere from 10 meter to hundreds of meters off the
target. You can’t do anything about DoD jamming satellites,
but you can make sure that your GPS receiver gets a very good access
to the sky. Recently with the implementation of WAAS (Wide Area Augmentation
System), a GPS receiver with WAAS enabled can get a very accurate
location fix by correcting errors caused by Ionosphere, Ephemeris,
Clock and more. (Again, read our GPS FAQ on WAAS). Some receivers
claim that they can get within less than 3 meters of the actual location,
which is very accurate for driving navigation purposes. Please note
that WAAS currently only covers North America. The European and Asian
systems will launch starting in 2004. I have not seen any DGPS (Differential
GPS) bundled in PDA GPS packages, only in stand-alone GPS products
from companies like Garmin.
So what should you do when you evaluate a GPS
receiver? Since you can’t try the product before purchase,
you can choose a WAAS enabled receiver if you need higher accuracy.
You should also read multiple reviews on the receiver and see what
the reviewer’s experience is like. One reviewer might experience
different conditions than the others. If they all have good results,
then you should be able to trust that receiver.
Usually the navigation software is considered the crown
jewels of the GPS package by your GPS vendors, because this part
is developed in-house, as opposed to licensed from other vendors.
Navigation software interfaces with your GPS receiver and hooks into
your map data, providing users with a easy-to-use user interface
that shows you the GPS status, allows you to plan your trips and
provides you with driving guidance systems.
Each GPS solution looks a little different and has
various bells and whistles that the others don’t have. You
can often easily find demos of the navigation software on GPS vendors’ sites.
I would suggest that you take a full advantage of these demos and
evaluate all the important aspects of the navigation software, such
as route planning, re-routing, guidance features, etc. For more GPS
navigation software info and screen shots of the user interface,
read our GPS product reviews.
Many PDA GPS vendors license map data and POI (points
of interest) databases from one of the big map makers. Most of the
maps are made in a similar way: get the basic info from the government,
like the county planning agencies, then incorporate that data with
aerial photos, satellite images, and get road updates from professionals
and consumers. Each map maker does something a little different during
this similar process and tries to get as accurate map data as possible.
For example, the data from the planning agency is good, but not accurate
because some buildings or roads may never get developed and the ones,
which have been built, take some time to make it into the report.
So some map makers will use USGS data, Census Bureau data, even police
and fire department to crosscheck the map data. Other map makers
develop better ways to incorporate photos data into their vector
You should know that there isn’t a single digital
map that is 100% updated. What can you do when you evaluate a GPS
solution that is bundled with certain map maker’s data? You
can often sample the maps of an area you are very familiar with.
This isn’t a fool proof as map coverage varies in different
areas. But it could be a good indicator of how detailed and extensive
the map data is. Here is a list of some major map makers and where
you can sample their data.
NavTech is one of the biggest map makers. They supply
most of the maps used by all major automobile GPS systems in the
US, and provide data to MapQuest.com. The way they update their map
is by using their field forces. They have over 100 field offices
staffed with analysts and engineers who drive miles and miles to
record fresh road info and POIs. Their map database is updated quarterly.
NavTech started out with only major city street-level maps and later
added maps to cover the whole country. Their street-level info includes
many road segments such as one-way street, turn restrictions and
more. You can use MapQuest.com to sample NavTech’s map data.
Tele Atlas is another big map maker who offers both
US and international map data. They supply their data to many transportation
companies. They also have a large field force that updates the map
data and POI database. Their new map database has a pre-eminent traffic
feed with over 350,000 traffic reporting locations embedded into
the maps. You can sample their maps on this site: www.mapsonus.com.
Rand McNally has been providing print maps Road Atlas
for a long time. StreetFinder, their digital map package, is very
popular, but they are mostly purchased from Tele Atlas and NavTech.
They also bought Thomas Bros. who makes very detailed street-level
maps for some parts of the US. Their city guides have a very extensive
POI database including many categories that other POI databases just
simply don’t have. You can sample their maps right on Rand
McNally’s web site. www.randmcnally.com.
Tiger, (Topologically Integrated Geographic Encoding
and Referencing system), isn’t a name you see often in map
bundles, but it contributes to many map-making processes. Tiger
maps are the product of the Census Bureau and are the source of
the US government’s map data. The maps are based on USGS
data and are not updated often. But their data does get incorporated
into other map packages. Here is a map view where you can check
out the map samples. http://tiger.census.gov/cgi-bin/mapbrowse-tbl.