LiDAR in Archaeology

Published by paulc on June 6, 2008 in Services and Technology. 0 Comments

LiDAR (Light Detection and Ranging) data is produced by attaching a laser-scanner to an aircraft. A cloud of measurement points across the landscape is produced as the laser-beam is fired at the ground and measured when it is reflected back to the aircraft.

Depending on how high the aircraft flies and how the raw data is processed, this typically results in a dataset of points spaced between 25cm and 2m apart, with a vertical tolerance of up to 20cm.

The highly detailed terrain models which can be produced from this data are incredibly useful for identifying archaeological features, even those which can barely be seen with the naked eye. In addition to the spatial component of the data, the intensity of the reflected laser beam is also recorded and this can be used to identify buried features where they cause changes in the vegetation cover or soil moisture content and hence the amount of absorption and reflectance of the laser beam.

Increasingly, this data is being used in our work. Wessex Archaeology has developed an effective methodology for the processing and analysis of such datasets. The biggest problem with these datasets is the volume of data, especially for large study areas. We have overcome this using the latest features in ArcGIS9, using appropriate data storage formats and processing routines capable of handling enormous datasets.

The latest project to make use of this approach to LiDAR data involved the processing of 19 strips of LiDAR data containing 133.5 million data points and covering an area of around 40 square km. This was processed to produce two multi-resolution Triangular Irregular Network (TIN) surfaces suitable for analysis, one for the elevation component and one for the intensity component.

These were used to produce derived analytical products such as hillshaded raster images and slope surfaces at the resolution of the source data (c.1m) ready for interpretation and digitisation of key features.

The advantage of processing this volume of data in one go is twofold. Firstly, any edge effects at the edges of the strips of data are minimised. Secondly, the amount of manual intervention is significantly reduced; had the data been processed in individual strips, it would have been necessary to undertake an additional stage of processing to clip and mosaic the datasets.

Much of this LiDAR data is being produced by the Environment Agency who are surveying areas of the country as part of their Flood Plain mapping programme. There is more information on LiDAR including how to obtain data and coverage maps on the Environment Agency website.

The image below shows an overview of the processed LiDAR data.

Example plot of LiDAR data

 

 

Vacancies: Archaeological Computing Specialists

Published by admin on March 14, 2008 in Vacancies. 0 Comments

Computing in the field. Literally..Do you want to work in the exciting world of archaeology? The way archaeology works is changing. Computers are becoming an essential tool for archaeologists, and used for everything from databases, geographic analysis, 3D visualisation, and web publication.We are looking for people with these skills and more (see our archaeological computing specialists advert for a full list) to join the Wessex Archaeology IT team. You don’t need to be an archaeologist to apply, but a healthy interest in heritage is essential!

Head over to our vacancies section to read more and download an application form.

The Stonehenge Landscape in 3D

Published by Tom Goskar on November 15, 2007 in Technology. 5 Comments

We have recently finished creating a short animation for the exhibition “Making History: Antiquaries In Britain, 1707–2007” at the Royal Academy in London. The three minute video demonstrates “Stonehenge revealed through digital technologies”.

It incorporates a fly-through of the Stonehenge landscape in 3D, based upon Environment Agency LIDAR (airborne 3D scanning) data, high resolution panoramas, and a new animation of the prehistoric dagger and axe carvings on Stone 53 at Stonehenge itself, from data collected by Archaeoptics Ltd.

During production of the animation, we turned the LIDAR data into a solid 3D model of whole landscape surrounding Stonehenge. Aerial tours of the most famous sites and monument groups were animated in HD (720i) resolution. What is exciting is that much of the upstanding archaeology, from well-preserved barrows to the subtle earthworks of prehistoric field systems, are clearly visible.

To do this, we had to work out how to use the data at 1:1 for our animations (for this kind of task it is often necessary to reduce the complexity of the data by half or quarter (1:2 or 1:4) due to enormous memory and processing requirements). This we achieved, and using lighting techniques we have been able to show the archaeology of the Stonehenge World Heritage Site as it has never been seen before.

This video focusses on the LIDAR data of the Stonehenge World Heritage site, including all footage as shown in the Royal Academy plus some of the footage that didn’t make the final cut. The version below is low resolution; to watch the footage in HD, head over to Vimeo.


A Virtual Stonehenge Landscape from Wessex Archaeology on Vimeo.

Smart Net

Published by admin on September 4, 2006 in Uncategorized. 0 Comments

We have been enthusiastic GPS users for a couple of years now but our latest acquisition of several Leica Smartnet enabled devices has changed the way we use the technology.

In the past when we needed to obtain accurate fixes for our survey work we have needed to log raw GPS data for several hours over one of our survey control points to process against the Ordnance Survey’s Active Station RINEX data. This sometimes meant that we had to be on site a whole day in advance of excavation teams. Smartnet uses the GSM/GPRS network to provide our rover units with real time correctional signals.

To begin with we upgraded our existing Leica1200 series GPS unit with a Smart Net GPRS unit. This allowed us to test the technology and check that we were getting the results we needed. A big concern was that we would have problems with GSM/GPRS cover - we tend to work in more remote locations than most land surveyors - so far though, Vodafone seem to have served us quite well.

In June we invested in a handful of Smartrovers - which were designed from the ground up to use the Smart Net technology and connect to standard mobile phones over Bluetooth. Again we were a little nervous - Bluetooth can be a temperamental technology - again we were very pleasantly surprised. The only time we have had serious problems with Bluetooth was when working near high tension cables.

We have now upgraded our old GPS500 rover unit to work with Smart Net. This is a very cost effective upgrade which gives the older equipment a very productive new lease of life.

Well, hello world!

Published by admin on April 5, 2006 in Uncategorized. 0 Comments

Welcome to our blog.

We are the IT Section of Wessex Archaeology. We are a mixed team of technologists, archaeologists, managers and practitioners who work together to support the rather varied computing needs of a large archaeology practice and its even more varied clients. As well as the usual geeky obsessions, our interests include database and web development, mobile computing, multimedia, GIS and survey technology as well as theoretical issues.

The postings here are designed to allow us to share our thoughts about the work we do. We will, of course, boast horribly about our successes but we will also complain about our frustrations and let you in on some of our (more realistic) plans for the future. Perhaps we will even persuade you to help us out.

Comments will be open but moderated to begin with so please do let us know what you think - but do try to be polite!