GPS and SatNav Pinpoint Accuracy Explained

As the use of SatNav systems increases among the general user population the misconceptions that have arisen on how these systems work are spreading. This article covers one of the author's favourites, the 'fact' or 'common knowledge' that GPS accurately pinpoint you anywhere in the world. This article is aimed at increasing awareness of what is really going on with accuracy.

Well, can anyone define pinpoint accuracy? It must vary as specs for different GPS units state different figures. My new Garmin handheld states less than 10m 95% typical with the proviso 'subject to accuracy degradation to 100m 2DRMS under the US DoD Selective Availability (SA) Program when activated'. I have had it down to saying 3m or even 2m in the higher accuracy differential mode (DGPS). However, whether to believe it or not at these better figures? A survey GPS unit states, Single Point L1 1.8m CEP (most will be explained later).

These figures are very very good, but are they pinpoint?

Let us keep analysing. Perhaps if it is good enough that it doesn't matter, it is pinpoint. If your GPS can get you close enough to use the best navigation system in the world, the Mark I Eyeball, then it has done its job. Depending on light/dark and weather this can range from a few meters to 10 miles or more. Is it pinpoint if it gets you to within 10 miles, where you can see your target, on a clear bright day?

I always thought the definition was, er, the point of a pin, less than 1mm. Only the best GPS left stationary for days will get anywhere near this.

Furthermore many talk of accuracy loosely without understanding. Even I have been loose with the term. There is accuracy, precision or repeatability and resolution, often with cross meanings to different people. Probably that is why many are loose with the term.

When someone says pinpoint I am tempted to ask for a figure and when and how often, resulting in the blank look. This brings in 95%, 2DRMS and CEP. Accuracy is defined as a statistical measure, it is pointless not to. The figure, for example,<10m is="" maybe="" the="" expected="" under="" best="" conditions="" rather="" than="" the="" average.="" these="" best="" conditions="" are="" where="" in="" the="" world="" there="" is="" full="" coverage="" and="" good="" satellite="" geometry,="" their="" position="" relative="" to="" the="" receiver.="" its="" all="" about="" angle="" of="" cut.="" an="" example="" of="" how="" often="" is="" the="" 95%,="" the="" accepted="" but="" not="" exactly="" 2="" sigma.="" 95%="" of="" recorded="" positions="" are="" expected="" to="" be="" within="" 10m="" of="" the="" true="" position.="" if="" you="" wanted="" 99%="" that="" would="" mean="" something="" in="" the="" order="" of="" maybe="" 15m.="" circular="" error="" probable="" (cep)="" is="">

Now for the anywhere in the world. Due to the orbital inclination you can expect less visible satellites above 55° north and south, less to choose from to obtain the required accuracy position solution. This is not the end for the position is also relative to some reference system and can cause issues if you are combining the use with a map.

GPS works on a reference system that is the best global fit. You may have come across WGS84 Datum. The world has a mathematically horrible shape, all lumpy and bumpy so only a best fit is viable. For some areas this is not a good fit so a different datum is used. Many of these precede GPS. The result is that plotting your WGS84 position on a map of a region of different datum can mean hundreds of meters out. For the car SatNav which is of proprietary manufacture this will be of no consequence as the map would, or should, come already referenced. If navigating with a hand held you need to know the datum for the area. Again the conversion sums are horrible but, no fear, most hand helds have most datums in the software, as long as you know this and where to find them you will be OK.

Essentially that pinpoint is more degraded by plotting on the wrong datum, something not always considered by many.

So there you go. If you arrive safely at your desired destination then the system has done its job. But lets not call it what it isn't.

There are other misconceptions but these are left for a separate article, 'GPS and SatNav. Removing Misconceptions' by the same author.

John Maris is a professional navigator and surveyor, offshore and coastal within the Oil and Gas exploration industry. With the increasing use of SatNav among the general user population, in vehicles, mobile phones and other applications, he is attempting to increase the awareness of users of how GPS, navigation and mapping combine to give us these systems. It is a fascinating and fantastic technology but not without its problems. A higher understanding of how it works will enable you to get the best out of your system, avoiding confusion and being misled. If interested in more detailed information then please visit http://www.azimuthnavigation.com/

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Next Wave in Smart-Phones, TVs and Tablets - Explained in Simple Terms

When you look at how manufacturing continues to evolve around us, in my mind I see 2 phases. And to illustrate my point, I'd throw up the automobile, locomotive and the aviation industry. The first phase, as I see it, began more than a hundred years ago, starting as new inventions, then evolving at a steady pace right up to the early nineties.

At around that point, a nascent electronics industry slowly but surely began to embed itself within these 3 industries and also every other, directly and indirectly. This catalyst for change brought us newer and more dynamic technologies at an astonishing pace; clearly no industry could ignore the benefits of electronics within. This for me is the 2nd phase that commenced in the early nineties right up to the present.

So there you have it. About a hundred years for animal drawn carriages to evolve to mechanical vehicles, and from then on, enhancements fly by so fast that our world is transformed in 2 decades and less. GPS guidance, pilot-less, voice or motion activated, satellite-tracked, iris scanning and many more widgets that have now become the standard. But latest models are only as good as the next release that's being readied for launch. From then on, it's that dreaded free-fall we know as 'depreciation', and the wait for the next model.

We'd speculate on whats next, because those at the forefront of innovation are now launching products that we didn't ever know we'd need. In the past, concepts and production were guided by market research and analysis, driven by you and me. Today, they're out in front of us, telling us what we will need in our futures. Production and shipping, is then only a few clicks away.

If you're a die-hard Black Friday or Boxing Day shopper, then my two cents on the next wave shouldn't faze you. Lets face it: nothings going to stop you from doing what you've got to do. In fact your last indulgence isn't a month old at the time of this article, so go ahead and enjoy your toy(s). My views are intended for those who'd wait for their next 'Objets désirés'. My notes just might help you take an informed decision. If my views interest you, then drill further with qualified resources & sites, as this is definitely not a techie article.

Smart-phones: The newest mobile communication standard is known as LTE (Long Term Evolution) that carriers tested with little publicity over the last 2-3 years. From what I know, Android & Windows mobile devices are early adopters, and Apple hasn't yet fallen in line. While LTE is described as 3.9G (just short of 4G), carriers are now preparing for 'LTE Advanced' that will meet 4G and beyond. There's a good chance the next iPhone will adopt this standard.

What this really means: No more latency in streaming or gaming; interactive content is going to come at you instantaneously. Your online experience would be super-fast!

TVs: Unless you live in a trade-embargo zone, you'd have noticed by now that prices of LCDs & Plasmas have been dropping so low that even those who don't watch TV, now have a large screen on their wish list. You could take advantage now, unless you'd prefer to wait for the next wave, which is a battle between 3D & OLED (organic light-emitting diode). While you already know of 3D, a quick interpretation of OLED is a thinner screen that emits a richer and a more vibrant experience than even LCDs or Plasmas! Several smartphones already use OLED and you can expect to see these in TVs within 2012.

Tablets: Somewhere around mid-year 2012, the dust should settle on the tablet wars and we'll see who is still standing. That Apple & Samsung will dominate is a no-brainer, but the question would be of whats changed with surviving contenders. In my view key features that would stand out are processing speeds, display screens and mobility. New models are coming at us this spring, and you already know which those would be. Whether you'd discard your PC for a tablet is also up for debate, but any which way, we can agree that (apps) applications are cutting to the chase for instant gratification.

Despite new versions, you've got to know that stretching your existing device is also an option, but only up until there's no further support or when irreversibly damaged.

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