Why did I buy a TomTom?

March 28, 2009 by
Filed under: Technology 

With PNDs (aka GPS) being launched all over we all want to have one, and I was no exception.  My wife and I were planning a trip to Alaska where we will be driving a lot. After weeks of comparative shopping, a couple of trials we ended up buying the TomTom Go-920.  TomTom, Garmin, Magellan, Sony, Nokia, and others have systems on the market.  Even some new cellphones have GPS functionality.

The PND (Personal Navigation Device) or the device you buy from Amazon is actually a sophisticated satellite receiver.  As you know,  GPS (Global Positioning System) is  a constellation of satellites that send time stamps to the receiver.  Yes, those multi-million dollar satellites are gigantic clocks circling the Earth.  The trick is that they are all syncronized.   By calculating the time of arrival of those time stamps and knowing the location of the satellites you can calculate the location of the receiver, aka get a fix (that is a geographical fix, if they included other kind they would be a bargain).  This process is called triangulation.  I found one of the best explanations of how how GPS works here.

TeleNav launched the Shotgun, a different kind of PND, a connected PND late 2008, not the first attempt at this category of PNDs.   Some advantages of a connected PND is that you can get real time POI (Points of Interest) updates, traffic, and weather feeds. But more importantly you can get a faster initial fix.In the triangulation process I described, besides the timestamps, the receiver needs to know the position of the satellites and then find at least 4 on site. It typically takes several minutes to find 4 satellites, but if you knew where they are, you’ll find them faster. Satellites follow orbits that are roughly known. The long term orbital positions of the satellites is stored in a file called the Almanac and short term variations are called ephemeris. Typically PNDs download the ephemeris from the satellites at a whopping speed of 50 bps (that is bits per second) so it is sloooow.  This file is valid for several hours and it is typically downloaded when the device is first turned on during a 24 hour period or so.  This can take up to several minutes. If you had a faster connection available to download the ephemeris you could get a much faster location of the satellites and a faster first fix. A connected PND such as the Shotgun or the defunct Dash has a cellphone like connection that can be at least 1000 times faster than the satellite. Hence, a connected PND can get the first fix in seconds. Good stuff.

Is that worth a $10 / $12 monthly fee?

This brings me back to my beloved Go.  By signing up to TomTom’s site you can get the ephemeris file from your PC via the connection utility before you leave home. It is valid for a bit more than 24 hours so you get the same effect for free.   The only thing is that you have to remember to plug it in every night after you come home, and take it back to your car before you leave.  The MapShare feature that Tom Tom has, where they allow you to correct errors on the map and share them with other TomTomers is cool, although not all corrections you receive from others are, well, correct.  There are lots of other things you can do at the TomTom site like downloading up to date gas proces (for a fee), all sorts of weird POI’s (and I do mean weird), and of course the ubiquitous software patches.

The traffic and weather feeds do require a monthly fee after the first 6 months. I tried them out but did not find them that that useful. Granted my commute is 20 boring miles and relatively light in traffic.  But if yours isn’t, you may want to consider the monthly fee.  And, there is a nice side effect with the monthly fee:  if you have a data plan with your bluetooth enabled cellphone, your Go can use it as a data connection and give you the feeds and the ephemeris file, turining it into a connected PND. Nice!

What really made us go for the Go-920 is the fact that it included Western European maps.  For a Garmin or Magellan you will have to shell out an extra hundred or so to get them.  I know what you’re thinking:  “didn’t you say Alaska?”.  I did, but it will be great for our next trip to Europe.  Wait we are in a recession, who know when that trip is going to be.  I hope maps haven’t changed by then.

In case you’re wondering, it worked great in Alaska.  Although the system is less precise the closer you get to the poles.  But Alaska’s highway system is very well marked, simple, and it is not easy to get lost in it, at least in the highways that you’re allowed to drive with a rental.

I have two pet peeves of my Go: the window mounting is a lot more reliable with Garmi and for some unkown reason, it tends to turn itself on and drain the battery.  Could it be the fact that it is Windows(r) based?




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