If you tune into BBC World Service, you may have heard the series 50 Things That Made the Modern Economy.Tim Harford tells the fascinating stories of 50 inventions, ideas and innovations which have helped create the economic world. The series asked for nominations on the 51st thing and Miranda Sharp, our Head of Smart Cities Practice, suggested GNSS (the Global Navigation Satellite System which encompasses GPS, the US’ Global Positioning System, amongst others). It made it to the shortlist and is open for votes until 6 October. Miranda explains why she nominated GNSS – and why you should vote for it!
I gobbled up Tim Harford’s latest series 50 Things That Made the Modern Economy. Tales of female emancipation wrapped up in TV dinners, tackling corruption through the technology of M-Pesa and enabling rapid transfer of ideas in an urban economy with the advent of the elevator. Listen to them all, buy the book, they are brilliant stories.
Australia has recently announced a 1.8m shift in its mapping coordinates, to compensate for the country’s 7.5cm shift north each year. Inevitably the question is why, and could the same thing happen here?
In Australia, the shift is to take into account the growing difference between maps (and the coordinate reference system they’re based on) and the system used by satellite positioning (GPS). It’s a fact that the world is constantly shifting on tectonic plates, but maps (and their users) like fixed coordinates that don’t change. Before GPS, this was simple to achieve as most positioning and mapping was created from fixed ground points in a coordinate reference system tuned to a particular country. In Great Britain our fixed points included the very familiar trig pillars and we have a mapping coordinate reference system called OSGB36 National Grid which is fitted closely to our little bit of the Earth. Tectonic plate movements had little or no impact on the mapping coordinates or fixed points because they all moved “as one” and generally stayed the same shape.
Talking about the 79th anniversary of the trig pillar this month has sparked a flood of reactions. Lots of our lovely followers on social media sent us pictures of them (or their dogs) with our trig pillars around Britain. Others expressed delight that they now know what those odd concrete pillars were for. Some wanted to adopt a trig pillar if we no longer used them (sorry, not something we offer). Still more people were amazed that we no longer use the vast majority of trig pillars and asked us what we use instead. The answer to that is OS Net.
Mark Greaves is our resident Geodetic Analyst
OS Net is Ordnance Survey’s network of permanent, high accuracy GNSS (Global Navigation Satellite System) receivers (see Tiree station below). A GNSS is a satellite system that is used to pinpoint the geographic location of a user’s receiver anywhere in the world. For OS Net, its day to day operation is to supply a stream of real time GNSS data covering the whole country. The data streams enable the correction of GNSS errors to be computed in real time and, when transmitted to our surveyors, allow them to coordinate new map features to an accuracy of just a few centimetres using RTK (Real Time Kinematic) GNSS.
OS Net data is not all about positioning. Another lesser known use is that it helps the Met Office predict the weather. Met Office scientist Dr Jonathan Jones explains…
We recently caught up with two of our Inverness surveyors to find out what challenges they face in their remote corner of Scotland. They mentioned mapping the changes at a hydro scheme and I thought it might be an idea to find out how we updated our OS MasterMap database to show the Glendoe Hydro Scheme, Scotland’s largest recent civil engineering project. Craig and Dave faced a technical challenge in finding the best way to map the new and changed topographical features.
The Glendoe Hydro Scheme is located in the hills above Loch Ness near Fort Augustus and although a significant part of the project is underground, many new and changed features needed to be incorporated into our OS MasterMap database. These included the dam wall, the reservoir, all of the access and service roads, changes to water courses and their associated walls and sluices, and changes to the extents of vegetation and other surface features.
The area was originally surveyed using photogrammetry and then published at a scale of 1:10000. Peter Todd, Senior Production Manager at Ordnance Survey said, “Photogrammetry would be the normal approach to revising a large area of change in a remote location, but our surveyors chose to work on the ground for a number of reasons: the development was classified as a prestige site so we needed to update our data before the official opening with Queen Elizabeth II; with unpredictable weather in the area we couldn’t guarantee we could fly over and take the imagery in time; and the reservoir would not be filled with water until just before the opening, so we would need to survey the edge of the water by ground methods anyway.”
You might have read my blog on Wessex Archaeology’s finds at our new head office, describing the Bronze Age Farm that was once on our Southampton site…while chatting with the team, based on the outskirts of Salisbury, I discovered just how much they rely on our data, both on paper and in numerous electronic formats. Talking to Paul Cripps, Geomatics Manager at Wessex Archaeology (WA), I discover that their mapping interests run from historic mapping to OS OpenData and a whole range in between.
Much of WA’s work is spatial, finding out how things relate to each other. From historic buildings to excavations to the marine environment, mapping is fundamental to everything WA do. But they don’t just use it as a backdrop, they add information about their excavations and finds too and attach that to their mapping. I was surprised to find that the historic mapping is not only needed to understand change through time but to ensure the accurate interpretation of aerial photography amongst other things; it is not always easy to work out what is shown in an aerial photograph alone and the feature may not be shown on more modern maps, a second world war bunker on a disused airfield can look very similar to a Roman fort from the air!
Paul explained to me how surveying techniques have changed over the years, “OS Net changed the way WA worked. We’ve gone from using measuring tapes to mark out the locations of digs, to using total stations (tied in to trig points) to using differential GPS units (which had to be set up 4-5 hours before work could start). SmartNet uses the mobile phone network and it only takes 5-10 minutes for us to start surveying and we capture 95% of all work with our Leica SmartNet devices. We still use total stations to survey areas where 3D recording is needed, such as buildings and structures, skeletons in graves and so on, but trenches and all basic features can be accurately captured using SmartNet.
“A lot of people wonder what we’re recording all the time, but initial digging on a site only covers a percentage of the area and you need to accurately map these locations. Basic info can be added onto the GPS unit as you work, then we process it in AutoCad or ArcGIS, attach our full database records to the surveyed features, add modern and historic mapping and have all the information we need in one spatial environment.”
WA have six SmartNet systems and want to invest in more as being able to do everything on site makes life much faster and efficient. Rather than a survey team driving around the country and setting surveys up, now the GPS systems are so simple that archaeologists can do the majority of work themselves after some basic training. This leaves WA’s survey specialists to work on training and standards (and still do some surveying too!).
There are some great examples of WA surveying on their website and loads more pictures of them in action on Flickr too.