British Expats - GPS recomendations please

Quote:

Originally Posted by withabix (Post 11634978)

TomTom launched some interesting updates for their current 'Go' series this week.

TomTom MyDrive new features

Installing the updates later today - looks interesting!

As for the mapping, TomTom owns TeleAtlas and also provide the mapping for iPhones. Garmin uses NavTeq. NavTeq belongs to Nokia company 'HERE', which it looks like they are about to put up for sale.

Between them, TomTom and Nokia provide mapping for every SatNav that's out there. Google is the only other mapping provider, but I don't think anyone else uses it.

All SatNavs use satellite signals from the USA NavStar GPS satellites or the Russian GLONASS satellites.

The US government or the Russians could turn off civilian access to their satellite signals at a time of war, making the entire world rely on maps!

At the same time, the world of land surveying would go back 25 years because just about every piece of survey equipment now uses GPS to obtain co-ordinates!

That is why the EU and various countries are launching satellites such as the European Galileo system.

The US, since the Clinton administration switched off the military Selective Availability system in 2000, has guaranteed free access to GPS constellations - so much so that new satellites built since 2007 do not support the feature at all. Other regional constellations include GLONASS, the Chinese BeiDou, India's IRNSS, Japan's QZSS (strictly, an augmentation to GPS, not a separate system), as well as the European Galileo system: commercial satnav devices will gradually support more and more of these, I suspect.

But, as you say, the navigation aids are only as good as the base maps the satellite data links to. TeleAtlas and NavTeq are much of a muchness, really, though Navteq's mapping tends to be rated more highly by users for accuracy.

Modern survey instruments, by the way, don't normally use the "raw" signal at all, except as an aid to acquisition of the satellite constellation. A survey instrument looks at phase shifts and timing markers in the carrier wave of the GPS signal to generate a very precise position, typically with corrections for atmospheric and orbital errors calculated from a local base station. There are various complex filters and error-correction algorithms embedded in the instrument, resulting in real-time position usually available to a couple of millimeters of accuracy for latitude and longitude, and a centimeter or two for elevation. That would make a geo-caching challenge fairly trivial!

/work intruding on BE conversation

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