We’re often asked about the work Ordnance Survey does, and unsurprisingly the role of surveyor crops up most often. I asked Tristan Shearing, one of our London surveying team, to give us an insight into his role…
When I tell people I work for Ordnance Survey as a surveyor, the most common response is ‘But isn’t everything already mapped?’. Confusion truly sets in when I tell them I work in an area of North London, far from the mountains and moorland they associate with Ordnance Survey mapping. When I explain that every time a house is demolished and rebuilt, or an estate is regenerated, or a prestigious new tower block is constructed, the London surveyors are on the scene taking measurements and updating the large-scale mapping, it starts to make a little more sense.
Last week we heard from the Flying Unit in our Remote Sensing team and this week we’re going to find out what happens to the images the Flying Unit send back to head office. As we capture around 50 000 aerial images of Great Britain every year, we need a team ready and waiting to process that information.
The Remote Sensing team take the imagery sent through by the Flying Unit and use it to update our large scale topographic database as well as populating products such as Land-Form PROFILE Plus and OS MasterMap Imagery Layer. We actually use the aerial photography to provide three key things:
• grid coordinates of features on the ground;
• heights of features and topography; and
• rectified photography.
Remote Sensing are split into sub-teams to manage these tasks. In Aerial Triangulation, simply put, they ‘pin’ the imagery to the National Grid and ensures that it is positionally accurate. Meanwhile Orthorectification use stereo imagery to assess changes in scale across the photography and produce a combined image which is geographically accurate. This becomes the OS MasterMap Imagery Layer and can be overlaid with other elements of OS MasterMap too. Finally, Data Capture use the stereo photography to measure height and location in order to update our topographic database. Imagery is viewed on a monitor using polarised spectacles to view two images virtually simultaneously.
So that was Remote Sensing 101 and you should have a rough idea of what the team do. I caught up with Jon, Peter and Nicholas to get their perspectives on their roles and discover how things have changed during their time in the team.
Jon has spent two periods of time in Remote Sensing and seen a number of changes between those two times. Part of Jon’s role is working on ‘knitting’ images together. If you think that the cameras on the aircraft are taking hundreds and thousands of images, then you need to find a way to stitch those images together to create one vast seamless image of Great Britain. The images need to be joined in a sensible means – you wouldn’t want a join across a feature such as a house or bridge for example. So Jon works with images, creating the joins and avoiding features, cutting around buildings and so on. Jon told me, “It’s known as seam lining and is especially challenging in built-up areas with large numbers of features and tall buildings creating shadows. It’s ideal to be working on somewhere like Norfolk – which is flat and relatively easy to do!”
Watching Jon and his colleagues work, my first observation, was apparently a very common one “doesn’t it strain your eyes working in 3D?” Jon assures me this isn’t the case, it’s more about relaxing your eyes and looking into the distance – much like with those 3D hidden image posters that were popular in the late 1990s.
I also wondered whether it had been more challenging for the team to move to our new head office. Jon said, “Now that we all work on PCs, we’re not that different to the rest of the building, so the move was quite simple. We just needed blinds up at the windows to make sure we could complete our screen work without any glare. Before PCs, when we had specialist equipment we needed reinforced floors to hold it all – and they had to be sprung to remove the vibrations from all of the equipment.
“We do have a different set up to most of the business as we work from two screens, with one in 3D. But other than the desks, we’re really not that different.”
Peter and Nicholas work on stereo plotting – making sure that things are in the right place in the simplest terms. They can be working on a variety of mapping scales ranging from urban sweep to mountain and moorland. They also undertake areas where it would be dangerous or access would be denied to our field surveyors, such as airports, refineries, railways, new motorways and so on.
Although my initial thought was that it must be great to have a rural area to check as there’s less change to identify, Peter pointed out that if you have a 5km by 5km area of Ben Nevis, you still have to check every section of it and be able to hunt out the smallest change.
Nicholas told me that he has seen many changes during his time in the team – and later this year the editing system will be changing again. “I undertook two months of training outside Remote Sensing before moving into the team. The analogue stereo plotting machines like the A8 and A10 took a long time to set up as you needed to recreate the position of the aircraft as it took each image. The current set up is more of a ‘trick of the brain’ using the dark glasses to create a 3D image on the screen rather than setting equipment up and looking through optics.”
Peter remembered the introduction of digital workstations around 2002. The digital photogrammetrical workstation (DPW) allowed for an on-screen display by which you could view imagery in 3D using special glasses. Peter also recalled the changeover to colour photography around five years ago and the switch to digital cameras. These have allowed the flying season to be extended, as he said “There have been many changes in Remote Sensing as it constantly evolves…we are now moving forward with a new system and I’m sure we will move on to greater and better things.”
Having a quick look through the specs that these guys work on, I have great admiration for the level of concentration required on a daily basis. I only wish I could show you the world as they see it – maybe once we have 3D computer screens as standard, I’ll do just that.
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 job of a surveyor is the one that we get asked about the most. People are fascinated by the people in hi-vis jackets that work their way around the country capturing the 5 000 changes made to our database everyday. Craig Methven and Dave Robertson work in our Inverness field office and told me what they get up to…
The prospect of the upcoming move to our new head office has resulted in buzz of increased activity around the building in recent months. Just like when you move house, it’s been a good time to have a bit of a clear out and take stock of what’s been hiding under the proverbial bed or in the attic.
Well, part of that process has included cataloguing the many pieces of antique surveying equipment that have been accrued by Ordnance Survey over the past 200 years. Some of the items have played an historic role in the birth of modern map making in Britain and are irreplaceable.
To understand more about some of this fascinating equipment, I caught up with Ken Lacey, a surveyor by trade who now works in our education team. Ken was kind enough to give me a tour of what is rapidly turning into an Aladdin’s cave of cartographic memorabilia, with two pieces being of particular interest.
Last week I wrote about an expedition to resurvey the height of Tryfan using modern GPS technology – the same technology the Ordnance Survey uses to map the country. Well, it was a great success and here is an account from John, Graham and Myrddyn. You can also watch an interview with our very own Mark Greaves on the BBC website.
The morning began dark and grey as we drove into the car park at Ogwen cottage, dark because it was just after 5am and grey because a fine drizzle had fallen on the valley.
Over the past year or so, I’ve been working with a group people who are on a quest to rewrite the map of Great Britain.
John Barnard, Graham Jackson and Myrddyn Phillips have been tirelessly climbing some of the country’s most famous peaks and measuring their heights using state-of-the-art GPS equipment. In doing so they have helped create mountains where once there were mere hills, and vice versa of course!