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Originally Posted by HSE2
A bit tough. With the advancement of portable Sat Nav systems in terms of performance and price a factory offering for well over double is behind the times. A bigger question would be how many people are buying portable Sat Nav devices and sticking them on the windscreen?
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The major difference in the price between the portable units and the inbuilt is that they use different technology.
The inbuilt units use accellerometers to track the movement of the car and only use the GPS to confirm positioning. This is why they work imediately on startup, in tunnels etc. or when there are few or no satellites available and do not get so easily confused if you take or miss a turn they do expect. They can also tell which direction you are pointed, whether you are reversing or going forward, whether you have changed to a side lane that is close to the main road etc.
All of the portable units work on GPS only and take time to start up (which can be anything from 10 seconds up to several hours when signals are bad) and can only tell you are in what direction or how fast you are moving by comparing your position to the last (few) positions. The often miss location fixes for whatever reason (usually interference to signals) and just assume you are following the predicted path. This is why they get so confused when you turn the wrong way and then play catchup.
I had one of each in my F6 and used to play games when I was bored making them track along different parallel roads. I was never able to trick the DENSO inbiult unit but have managed to confuse the hell out of Navmans, TomTom, Magellans and Route 66.
So in summary, the protables are nowhere near as clever as the fixed units but if they do the job you want then buy one, if you want better then buy the inbuilt.
A FG XT has the same number of seats, will do the same maximum legal speeds and carry the same amount of groceries as a FPV GT-E (or F6-E).
The FPV just does it all a whole lot better......