Wednesday, Jul 27, 2016 at 21:21
Hi Phil
You are probably correct but the lack of GPS satellite visibility is often just the start of the problem. A lot depends on the functionality embedded in the GPS chips. I ran a big survey company for many years and probably know enough to be dangerous on the subject. So for what it's worth here goes.
1 GPS coverage over Australia is quite poor compared to North America and Europe. If you really want decent coverage here you need a GPS chip that "sees" Glonass (Russian) and GPS satellites. It is very unlikely that these chips are in consumer devices.
2 Each GPS satellite has a unique orbit and identifier. A GPS chip may or may not have the capability of updating this empheris detail. If not the chip takes a long time to find a satellite and to calculate where it is on the WGS84 spheroid. So if you lose GPS lock and are on the move the chip may be looking for satellites that are now out of view.
3 Each chip set has different setup parameters. I have no knowledge of the defaults that have been setup in consumer products but I would expect there is a timeout function to save power. This may cause the chip to stop searching for sats until the next power up. Also the manufactures of the chipset will change the setup depending on its application. eg parameters will be different if your walking around vs flying in a jet. Where you may be will be very different in one minutes time.
4 The GPS signal is incredibly weak. It lives within the "white noise" frequency of background radio. The interior of a car is a very noisy environment and as you have stated the windscreen and car direction of travel limits the GPS view significantly. Dedicated car navigation GPS units use historical trajectories and internal logic to synthesise positions when GPS position ( at least 3 sats in view) is lost. Such functionality is not likely to be in consumer products not designed for navigation.
To be frank I am amazed at how will these cheap GPS chipsets work in a car without an external antenna. The rural environment is the best where man made
infrastructure, that causes multipathing etc is least, provided that you are not in heavily forested or mountainous country that obscure the view to the satellites.
Having had similar problems to the author of the thread I have generally solved the problem by taking the device out of the car, allowing it a good view of the sky, and waiting until it re- establishes satellite lock, then moving off.
Hopefully this has been of some use to somebody.
Cheers
John
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