Choosing a handheld GPS device

Choosing a new GPS DeviceLove them or hate them, GPS devices are rapidly becoming more popular for all kinds of outdoor pursuits. They can be used for checking your position, following a pre-defined route and automatically recording your route. Some offer additional features, such as cameras or altimeters. Here’s the Ordnance Survey guide to choosing a handheld GPS device.

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Walking with a GPS

Handheld GPS DeviceA Global Positioning Device or GPS is a very handy tool for walkers who want the security of knowing their exact location. If you’re walking somewhere relatively featureless then a GPS provides the peace of mind that you’re going in the right direction. It will also allow you to give the emergency services your exact location, should you get in a spot of bother and need their support. Continue reading “Walking with a GPS”

How do we survey the changing face of Britain?

One of our surveyors at head office

Keeping the master map of Great Britain up-to-date is no easy task and sees thousands of changes a day made to our database. We capture these changes on the ground through our team of 240 surveyors equipped with the latest positioning technology and via Remote Sensing, with both our own Flying Unit and strategic suppliers capturing aerial imagery which is then processed back at head office.

The latest technology makes the task of capturing change on the ground faster than ever before. Our surveyors are usually home-workers and keep the GI data up to date within a set area. They work on a Panasonic Toughbook – a ruggedised convertible notebook computer which serves as both their laptop and data collection tool. It’s both showerproof and dustproof which is essential for a job largely carried out in the great outdoors. It connects wirelessly to their GNSS equipment, electronic total station and hand-held laser rangefinder. It’s also the means for them to connect to head office, arrange and order data for jobs and send data back again.

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Solar Flares – the impact on OS Net and GPS

Space weather is once again in the news – with a big solar flare hitting Earth this morning.

Solar flares are related to sunspot activity which tends to run in 11 year cycles. We’re now in the period where sunspot activity is increasing to a maximum for the current cycle. This morning’s flare is the biggest for 5 years – and tonight there is a chance Scotland might even get to experience the Northern Lights as a result.

However Solar flares can disrupt electromagnetic communications especially ones involving satellites. Solar flares increase the electromagnetic activity in a part of the Earth’s atmosphere called the ionosphere. This increases the impact of the ionosphere on GNSS signals (the generic term for all the navigation satellites orbiting the Earth, like GPS).

In the context of OS Net, our national network of 110 satellite receiver stations that make precision map making possible, a period of bad ‘space weather’ can make our work much more difficult. It makes satellites harder pick up and track from the ground. Also, in order to calculate an accurate position, the effect of the ionosphere must be modelled and then removed. When ionospheric activity is high and changing rapidly (like it is at the moment) this modelling is much more difficult.  Space weather is also bad news for users who derive accurate timing from GNSS such as to synchronise computer and communications networks.

During a space weather event, GNSS users may experience a loss of satellite signal or errors in position or timing. Using a network of  dual frequency satellite receiver stations, like OS Net, as opposed to a single base station solution is the best way to mitigate the effects of bad space weather. Processing data from a network of base stations allows for the best possible real time modelling of the changing effect of the ionosphere. This means more robust data is sent to our 250 surveyors working to map the changes across the country.

In the meantime, we’re working hard to make sure the affects of this current period of bad weather have as little impact on our work and the people who rely on our data, as possible.

The data from a national network of high precision, dual frequency receivers such OS Net is also useful to predict and monitor the impacts of space weather on the positioning and timing community, these receivers are capable of directly measuring the ionospheric delay of the satellite signals as they travel down to earth , unlike standard GPS receivers. Ordnance Survey are also a partner in SENTINEL – a Technology Strategy Board sponsored research project to monitor the impact of such things as space weather on GNSS signals.  The data collected by OS Net stations and SENTINEL “probes” across the country during today’s event will make an important contribution to the research in to the impacts of space weather on GNSS signals.

There is some more information on solar flares from the British Geological Survey Twitter feed, whilst if you’re after a more technical article on the impact of space weather on GNSS can be found here.

Osmington White Horse – an update

A few months ago, we told you about the work we have been doing with The Osmington White Horse restoration team to help them to restore the figure to its original form. So, as the winter sets in and the team are no longer on the hill, I thought you might like to hear about how it’s gone and what’s happening next.

The Osmington White Horse is a figure cut into the hill just outside Weymouth Bay. The figure of George III on his horse was originally created in 1808 and is enormous at 85 metres long and nearly 100 metres high. It’s on a very steep slope which can be seen from Weymouth Bay which will host the sailing element of the Olympics in 2012.

Although there have been a number of spasmodic maintenance and restoration projects over the years (including Challenge Anneka in the 1980s) the figure had deteriorated badly and the original figure had become overgrown and ill-defined over time.

The project to restore the figure started in 2009 by The Osmington Society – an amazing group of local people with a desire to improve the heritage in their area. They enlisted the support of Natural England, English Heritage and Ordnance Survey to help identify the original outline. Continue reading “Osmington White Horse – an update”

Lost? Follow that satellite dish!

I read a great article on the BBC recently that was giving tips on finding your way in a city. Did you know that most UK satellite dishes (all belonging to the same provider) point roughly south east? They’re pointing at the same geostationary satellite, fixed at the same point over Earth. 

We’re all becoming increasingly reliant on having a GPS signal to know our location – whether it’s to find your nearest cinema/petrol station/restaurant on a mobile phone, following the soothing tones of your satnav, or plotting a route for your next countryside walk. But what happens when you lose your GPS signal, or your battery dies on the device you’re using? 

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Will 4G mobile broadband spell the end of GPS?

A battle is raging on the other side of the Atlantic.

It’s a battle about use of the airwaves, or more precisely “radio spectrum,” by two rival American technologies.

In one corner is the well established Global Positioning System (GPS), the enabler of location services the world over. Facing up in the opposite corner is a fourth generation (4G) mobile broadband network from a company called LightSquared.

LightSquared is currently seeking a Federal Communication Commission (FCC) licence to operate its network and proposes to ultimately install around 40,000 transmitting beacons across the USA.  The network will also be supported by a satellite that is already in orbit.

Our surveyors rely on GPS technology everyday.

The nub of the problem is that the band of radio spectrum allocated to the LightSquared network is adjacent to the band allocated to GPS.  This causes interference to GPS because the LightSquared signals are much more powerful and therefore swamp out the weak GPS signals.  The interference problem has been confirmed by two independent tests.

This is a major problem.

GPS and other satellite systems such as the Russian GLONASS and upcoming European Galileo are now heavily relied upon, not only for positioning (we use the service day-in day-out to help keep Great Britain’s mastermap up-to-date) but increasingly for providing accurate timing, for the mobile ‘phone networks for example.

They are also starting to be used as part of “Safety of Life” systems such as aircraft navigation and landing.

Both camps are lobbying the FCC and fighting their corners.

GPS supporters have formed the “Coalition to Save Our GPS“ whilst LightSquared are arguing that GPS has had an “easy ride” and for too long has been allowed to leak outside it’s allocated spectrum.

Save Our GPS

LightSquared have offered a change to the proposed network which involves using different frequencies and lower power at the base stations which they say limits the interference.  However they are also arguing that GPS receivers should be forced to update so that they filter “out of band” signals such as LightSquared’s and also operate more closely in their allotted spectrum.  It would obviously be a long an expensive process to implement this solution.

At the moment, the issue if confined to the United States, but commentators in Europe are also watching the debate with interest since the developing Galileo service uses some of the same frequencies as GPS.

We can expect this fight to rumble on for some time yet…

How do you measure a mountain?

In the past week of so, you may have read about plans by Nepal to re-measure the height of Everest. Apparently being the world’s highest peak at 8,848m just isn’t enough – they want to use the latest satellite technology to get the most accurate measurement possible.


It’ll also an opportunity to settle a long standing disagreement between China and Nepal. According to the BBC, the Chinese argue Everest should be measured to its rock height, while Nepal maintains that any figure should include the snow on the summit – which would add about four metres.

This in itself is an interesting debate – what do you think is fairer?

Anyway, it’ll be two years before we hear the results, so in the meantime I thought it would be worth explaining how you actually go about measuring something as huge as a mountain.

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Up in the air

I’m sure most of us have been more than happy with the lovely sunny, dry weather this spring, but how many can say that it’s helped them complete their work too? Personally, I’ve given more than one resentful glance out of the window at the glorious weather – not while writing for the blog of course! – but my colleague John has been embracing it whole heartedly. 

One of the planes our Flying Unit use

One of the planes our Flying Unit use

John is part of the Ordnance Survey Flying Unit. Working as part of our Remote Sensing department, the Flying Unit could be in the skies anytime that weather allows between early March and November.


Five people, some from our field teams and others from head office, work on a rota from our Blackpool airport base during the flying season. The two people on the rota spend around two weeks at a time in Blackpool, flying as often as the weather permits, including weekends.

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Why 'space weather' is bad news for map making

What is ‘space weather’? Well this generally means solar flares – or as you might have heard on the news recently – coronal mass ejections to give them their full title!

Solar flares are related to sunspot activity which tends to run in 11 year cycles. We’re now entering the period where sunspot activity is increasing to a maximum for the current cycle. On Tuesday there was a big flare – the biggest for 4 years - whilst tonight those of you in Scotland might even get to see the Northern Lights as a result, so keep your eyes on the skies!

Solar flares

A solar flare

So what’s all this got to do with mapping?

Continue reading “Why 'space weather' is bad news for map making”