Interview: Historic Scotland Director David Mitchell On Laser Scanning UNESCO Sites

Over the next four years, the Scottish 10 project will see a joint team from Historic Scotland and the Glasgow School of Art make cutting-edge laser scans of a decade of UNESCO World Heritage Sites in Scotland and across the globe. Among them will be all five of Scotland’s entries on the list – the Antonine Wall, New Lanark, the Heart of Neolithic Orkney, the Old and New Towns of Edinburgh and the island of St Kilda – plus five other sites internationally, starting with Mount Rushmore in the United States.

David Mitchell, Director of Historic Scotland’s Technical Conservation Group, is heading the project. He talks to Heritage Key about the nifty new tool that is set to revolutionise archaeological and architectural surveying across the world, his team’s contribution to the so-called “Global Alexandra Library” and standing on the head of a Founding Father.

HK: Give us some background on the Scottish 10 and the genesis of the project.

DM: We’ve had a research relationship with the Glasgow School of Art for about three years now. The first time we saw the potential really for laser scanning and visualization was the work that the art school had done on the Glasgow Urban Model. I thought that was really interesting. I knew that laser scanning had been used in archaeology before, but that it hadn’t really been used in standing buildings before.

So we’ve embarked on a bit of a journey with them over the last couple of years, with pretty spectacular results. We’ve come a long, long way really quickly. The Scottish Minister for Culture, Michael Russell, came into his post in the Spring – we had him open the Digital Documentation Conference that we ran in Glasgow with the art school. He got really excited about the technology. Then we met Ben Kacyra from CyArk – Ben is the man who invented the laser scanner, who we’ve become pretty friendly with.

Ben is pushing something called the World 500, which is a project to record 500 World Heritage Sites in the next five years, which is pretty ambitious. The Culture Minister was fairly enthusiastic about that, and agreed that we would do the five World Heritage Sites in Scotland, and do five World Heritage Sites overseas. So that’s the genesis of the project. We’re about 80% complete on New Lanark, which is the first one, and we’re due to go out to Mount Rushmore in the Spring.

HK: What are the goals of the project? You’re creating 3D renderings of the site – is that for preservation purposes?

DM: Yeah, it’s kind of a broad mix. It’s a snapshot – an archive record – which is one thing; that’ll get done in part with the Royal Commission in Edinburgh. And part of it is a snapshot of the site in 2009 or 2010. It’s different uses for different sites. Some will make more use of it as an educational tool. In Orkney we’ll use the data for managing the site, looking at things like sea-level change and at sites, such as Skara Brae, where things like coastal erosion are an issue. We want to do a wee bit more than going into the sites, scanning and coming back again – we’re looking at a sort of technological legacy being left in Orkney with the archaeology unit there, so they’ve got the capability to laser scan there in the future.

The overseas stuff – there’s a bit of altruism there, but there’s also a lot of economic and cultural reasons for it. It’s interesting the reactions in the US – there’s been a bit of surprise in the surveying community there that these Scots are coming over to scan one of their important national monuments for them. Most of them have given us credit for where we’ve got to with the technology, and the exposure that the technology’s getting – because it tends to sit in the surveys world by and large. And, you know, motorways and drainage ditches aren’t as exciting as Mount Rushmore or the Taj Mahal!

HK: As well as Mount Rushmore, what are the four other sites internationally that you plan to scan?

DM: We’re still discussing them just now. The Culture Minister is very interested for us to do something in India, and the obvious one is the Taj Mahal, but we’ve had no contact with our counterparts in India. Also, we’re keen to do something in China and something in South America. We’d like to do one that’s technically really, really challenging and slightly bonkers. There’s a site on the UNESCO Sites In Danger list – it’s a saltpeter mine on the plains in South America (the Humberstone and Santa Laura Saltpeter Works in Chile). I just think the logistical challenges are really exciting, and also it’s a site that’s really at risk. We’re being quite open-minded about it at the moment.

HK: Give us an insight, in layman’s terms, into how the laser scanning technology you’re using works.

DM: Ben Kacyra had a very big engineering firm, and he did a lot of after-build as-built projects at oil refineries, power stations, that kind of thing. His team would go in, and they would actually do as-built drawings, because invariably these things were never built as designed. To him, this seemed a monumental waste of time and resources. He was exposed to some early work in laser scanning and it piqued a little bit of interest with him; at the end of the Star Wars programme in the US, quite a lot of the technology was made available and he basically took advantage of the work that had been done using lasers, and persuaded Mobil to fund the research and development for the first laser scanner.

In principal it’s really simple how it works. You fire a laser from the scanner, it hits the surface of the building, it bounces back, and because we know the speed of light, we measure half the time it takes to hit the surface and bounce back and it creates a dot. So the laser will tick its way across the surface of a building, returning lots and lots of tiny dots, which we call a point cloud.

A very clever piece of software then allows you to generate that point cloud up on your computer and mesh the scans you take from different locations together. You basically get two outputs from it – you get an X, Y and a Z coordinate, and you also get a reflectance value, because each material has its own properties. It’s something of interest to us recently that you can match a reflectance value to a particular material, so we could use it potentially to identify stone-types and that type of thing, although that hasn’t been looked at yet.

HK: Of the sites in Scotland, which are you personally most excited about seeing scanned?

DM: That’s a good question; nobody’s asked me that before! I’ve got a soft spot for New Lanark, because I’m really interested in industrial archaeology, and I can really see the potential on the education side at New Lanark, showing things like the development of the site, how the water crosses the works and stuff like that. And Edinburgh is one that really gets me too – Edinburgh is so big, and to do a city model on that scale is something that’s never been done that successfully before.

City models have been done in Germany before, and there’s one being done in Istanbul, but at nothing like the resolution like we’re talking about here. We’re going to pick away at Edinburgh for the next couple of years; we’re going to have a team from my science unit and a team from the Glasgow School of Art, but it’s going to take us two years, realistically.

HK: How long has New Lanark taken?

DM: We’ve probably got about a week’s worth of work left, and I’d probably say that we’ve taken about three weeks in total. Which is incredible. At rough estimate we think it’s about 80% quicker to do a laser scan than it is to do a normal building survey, and with a normal building survey you get nothing like the amount of measured points that you get from laser scanning. So the quality of the data is much, much better.

HK: Is it quite exciting to see the data from New Lanark coming in?

DM: It’s incredible. The first time you look at a points cloud it just looks like a jumble of dots. But when you get used to looking at it and understanding what it is, it’s a bit like looking at a thermographic image of a building, which shows the heat emissions form the surface – it’s quite engaging. The points could is like that, and it allows you to look at buildings from a slightly different perspective.

Doug Pritchard (Head of Visualisation at the Glasgow School of Art) always talks about this, and he’s absolutely right – we see everything in three dimensions, but for hundreds and hundreds of years, we’ve interpreted them in 2D drawings or sketches. When you see things in 3D, you should be able to represent them in 3D. We find that when you’re dealing with lay people, if you show them a 2D drawing of a building, their eyes usually glaze over. But everyone can understand a 3D model, because that’s what you see with your eyes. So it’s a really engaging tool I think.

HK: Each site must present a different challenge – Edinburgh is very large, Orkney is very small. With St Kilda, it must be the remoteness?

DM: Yes, that’s one my staff have told me I have to go and do! St Kilda’s going to be amazing to do. We’ll do a survey of the archipelago, and from the scanning point-of-view we’ll be doing the main points of habitation. One of my colleagues has been out a couple of times and he says it’s just like landing on the moon. So that should be really exciting.

HK: Mount Rushmore must present a whole different set of challenges again?

DM: It does. We’ve been out and done a recce at Mount Rushmore, and it was one of those point when I realised I’ve got quite a privileged job because I get to be places where people aren’t normally allowed to go. I stood up on the top of George Washington’s head, which was completely bizarre!

From a scanning point of view it’s quite straightforward, because the granite it’s made from is absolutely perfect. It’s the logistics – there’s no road access at all up to the head. There’s quite a big scree slope at the bottom where they basically blasted the rock off and it’s quite dangerous – I took a tumble down the hill when I was there and ended up in hospital, which was not fun. It was quite sobering for the guys – made them think, “you know, this is dangerous.” It’s getting the kit up to the top of the hill and moving it about into position – that’s the tricky bit with Mount Rushmore. But you’ve got to deal with things like that.

HK: What’s the long-term plans for application of the models of the sites? Is it something that will go on public display one day?

DM: Yeah, absolutely. We’re doing this project with CyArk in the US, and CyArk are talking about being the “Global Alexandra Library” – they want to be the global depository for this kind of data. They’ve got some really nifty bits of software that allows people to visualise the points cloud and play with them and measure points and that type of thing. All of that will be made available on CyArk’s website. There’s been huge media interest in this, and we’ve been talking to National Geographic about potentially doing something with them. On the education front, this stuff will be available on the Historic Scotland website, and the New Lanark site I’m sure will definitely have some publicly available material on this.

HK: It must feel great to know that your team is gaining an international profile?

DM: It’s really nice, because we’ve been working away at it quietly for a couple of years. The first time that we realised there was real interest, Doug Pritchard and I did a presentation to a laser scanning conference in California in 2008, which is the big international conference, and the audience was completely blown away by what we were showing them, because they hadn’t seen any of the type of heritage site stuff like this. There’s been some really great stuff done at Queens University in Belfast, and the University of Ferrara in Spain do some superb stuff, but we were the first people to joint the high-end modeling on the point cloud itself.

It was actually quite a shock for us, because there was a deluge of interest from there with people wanting us to come to speak to them. It’s generated a huge amount of interest.

HK: Are there any other sites in Scotland that you personally would like to go and scan?

DM: Probably loads of industrial sites. One of my favourite ones we did is a tiny woolen mill up in Grampian that’s practically held together with bits of string and sellotape. I like the kind of weird and wonderful. We did a scan at Rosslyn which was fun, just because of the connotations of Rosslyn. But I’ve got a notion to do something like one of the old lighthouses. The big one is the Forth Rail Bridge. Ben Kacyra used to be a bridge engineer, and we have this sort of ongoing rib with each other about whether the Golden Gate Bridge is more attractive than the Forth Rail Bridge.

HK: Do you think laser scanning technology is something that we’ll see used widely by archaeologists and surveyors in time?

DM: I think that’s inevitable. Just now the hardware is quite expensive, but in time it’ll become like a handheld tool or a laptop or something, and the cost of the technology will come right down. The software needs to evolve a bit, it’s still quite clunky in places, but that’ll sort itself out in time. For people who go out and survey sites day-in and day-out, it’ll become just another tool in the toolkit.

Pictures from Historic Scotland. All rights reserved.

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