GPS In The Canyon

October 10, 2006 by Mr. GPS · 2 Comments
Filed under: GPS Busses, GPS Cabs, GPS for Business 

London tests satellite tracking

TfL could use satellite technology for more flexible road-use charge

Dave Friedlos, Computing 05 Oct 2006

Transport for London (TfL) has completed a London-wide test of satellite tracking technology with a view to establishing more flexible congestion charge pricing.

Computing has learned that TfL tested a number of devices, including custom-built in-vehicle units and PDAs, to track cars accurately through London streets.

The trials were staged to gather route data and overcome common problems such as loss of signal when a vehicle enters a tunnel, or passes through a dense block of tall buildings… Full Article Here:

Lately I seem to be running heavily to British subject matter, but I can’t help it, I only report the news as it happens. I wrote about Transport for London earlier. TfL will be installing GPS tracking on buses, reporting back both to dispatch centers and public information kiosks to improve transport efficiency and increase ridership (as in profit and more profit).

As you ca see from the quoted article there also a lot going on regarding Pay As You Drive (PAYD) toll, taxation and cutting down city traffic by offering incentives for off-peak traffic use. It all sounds great to me, except for one thing.

The dreaded urban canyon effect. When a GPS receiver can view a large part of the sky … on the order of half the sky or more, it will work great. There are virtually always 12 satellites in view from anywhere on earth and a receiver needs on four satellites to get a decent “fix”. However, when you are down between tall buildings in a big city … the so-called “urban canyon”, GPS can come up with wildly inaccurate readings or just shut down altogether until more ’sky’ becomes visible.

This is well known, long known and, in my view, is a black eye on the face of many GPS manufacturers. They just ignore the problem instead of bringing out receivers that could cure the problem.

The best solution is a dual-mode GPS chip that takes positron from the sky when available and runs in a self-contained inertial mode when not enough satellites are in view. Inertial navigation is a much older science than GPS. It involves sensing the movement and direction of a vehicle and then calculating the vehicle’s position from where it was last know, Many years ago this was an expensive, mechanically complex undertaking. Today there are inertial navigator self-contained chips that are roughly the size of pure GPS internal chips. There is an added cost but most of that cost would go away rapidly if manufacturers just realized they were in the navigation business and not the GPS business. GPS receivers today are a fifth the cost that they were 2 years ago and the price continues in free fall. Add on inertial capability would fall just as rapidly if anyone decided to live up to their responsibilities.

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  1. GPS Tracking » Blog Archive » GPS PAYD ROI — Have They Thought This Through? says:
    18/01/2007 at 05:50

    [...] A lot of stories are landing in the in-box lately about PAYD (Pay As You Drive) schemes.  I’ve been covering the subject often,here, here, here and here for just a few reports.  What we need to do here is separate the idea of PAYD from the somewhat ill-thought out technical solutions being proposed by officials ignorant of technology and some vendors who seem eager to sell a solution, even if it’s wrong. [...]

  2. Cutting Through The Fog With FOG Makes GPS Tracking Better | GPS Tracking ROI says:
    17/11/2007 at 03:03

    [...] Sometimes this gap in reception is caused by the “urban canyon” (see here and here for some Urban Canyon background) effect.  Other times there may be actual physical [...]