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studarude
Occasional Visitor
Joined: Nov 26, 2006
Posts: 2
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 Posted: Tue Nov 28, 2006 4:51 pm Post subject: Do GPS systems need line-of-site to pick up satelites? |
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Hi people, im just in the process of wading through the myriad of available gps systems, when i had a thought, do gps need a clear line of site into the sky? ive got a snooper gps based camera detector which does, and as my car has a heat reflective windscreen on most occassions takes ages to pick satelites up, am i going to have the same problem with a gps navigation system?
thanks. |
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kartracer
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Joined: 26/03/2003 20:15:33
Posts: 502
Location: United Kingdom
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| Posted: Tue Nov 28, 2006 4:58 pm Post subject: |
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The short answer is, yes. Although recently it has become a bit less vital as receivers have become more sensitive.
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Border_Collie
Pocket GPS Verifier
Joined: Feb 01, 2006
Posts: 2543
Location: Rainham, Kent. England.
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| Posted: Tue Nov 28, 2006 5:35 pm Post subject: |
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| Quote: | as my car has a heat reflective windscreen on most occassions takes ages to pick satelites up, am i going to have the same problem with a gps navigation system?
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Athermic windscreens can cut the signal down quite a bit and can take ages to lock on, but it's not as bad with the newer SiRF3 chipset.
There is usually a clear area in the screen, black dotted area just behind the rear view mirror, so set your unit up in the centre of the dash.
I always get 5 or 6 sats. locked before entering the car, once locked it doesn't really cause any problems.
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Formerly known as Lost_Property
And NO that's NOT me in the Avatar. |
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neil01
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Joined: May 06, 2005
Posts: 902
Location: Leeds
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| Posted: Tue Nov 28, 2006 6:16 pm Post subject: |
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Expanding on what Lost_Property said about getting a fix first and without getting technical; due to the nature of GPS, It is much easier to get a fix whilst stationary, and it is infinately easier for the hardware to retain a fix than it is for it to get one in the first place.
As for line of sight - you also need to remember that 'line of sight' is different for GPS signals than what we consider line of sight. For example, a GPS signal can even penetrate a certain distance through some walls into buildings, which we obviously can't see through at all, yet as mentioned, 'Athermic' windows cause (varying degrees of) problems for GPS hardware, yet we have no dificulty seing through them. |
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deepeejay
Occasional Visitor
Joined: Nov 06, 2006
Posts: 9
Location: Extremadura SW Spain
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| Posted: Tue Feb 27, 2007 11:16 pm Post subject: Re: Do GPS systems need line-of-site to pick up satelites? |
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| studarude wrote: | Hi people, im just in the process of wading through the myriad of available gps systems, when i had a thought, do gps need a clear line of site into the sky? ive got a snooper gps based camera detector which does, and as my car has a heat reflective windscreen on most occassions takes ages to pick satelites up, am i going to have the same problem with a gps navigation system?
thanks. |
Think about getting a unit with bluetooth then buy a small GPS receiver and stick it on the rear parcel shelf where it will easily detect sufficient satellites. I use such a receiver in my Citroën C5 with an Acer N50 PPC.
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Dave J
In sunny Extremadura
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nbg
Regular Visitor
Joined: Dec 21, 2006
Posts: 63
Location: Bristol
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| Posted: Wed Feb 28, 2007 6:07 pm Post subject: |
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| I guess it depends on the unit. My TT 910 has a singal in the living room of my house and in the space next to the gearstick and handbrake on the car :D |
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philpugh
Lifetime Member
Joined: Dec 28, 2005
Posts: 2003
Location: Antrobus, Cheshire
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| Posted: Wed Feb 28, 2007 6:45 pm Post subject: Re: Do GPS systems need line-of-site to pick up satelites? |
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| studarude wrote: | Hi people, im just in the process of wading through the myriad of available gps systems, when i had a thought, do gps need a clear line of site into the sky?
thanks. |
Line of sight is highly recommended. Picking up secondary reflections (the 'urban canyon' scenario) can cause a false location as your location is calculated using very precise time information recieved from all the satellites and reflections will cause an added distance for the signal to travel, giving a false timing for one or more sats. Perversley the more sensitive receivers could be affected more by this. This is one of the causes of 'position wandering' when physically stationary. Others include atmospheric refraction which causes similar timing diferences, especially noticable for sats that are low down in the sky. Usually the error for these sorts of conditions is insignificant in terms of road navigation as it will be within the lock-to-centreline - but occasionally they add up to give wandering car syndrome. 
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