Computing

Web mapping and archaeology

Paul Cripps — Tue, 07 Oct 2008 11:43:36 +0000

With the rise in popularity of online mapping sites such as Google Maps, Yahoo! Maps and Microsoft Live Maps, more and more people are creating maps and spatial ‘mashups'. The only thing holding many people back has been the need to work with the published APIs (Advanced Programming Interfaces) for such platforms, requiring some understanding of programming and HTML. Such platforms have enabled users to create maps showing all kinds of things: locations of photographs from Flickr, places visited, archaeological sites, etc, etc. Pretty much anything with a spatial component to it can be (and, in many cases, has been) mapped in this way; a really good example of the technology with some great archaeological content is the Online Archaeology map, created by Steve White.

Here at Wessex Archaeology, we are using these technologies to improve access to our geodata within the organisation. We have an installation of PostGIS to store core datasets, such as those provided by English Heritage, and a Geoserver to make these available as Web Mapping Service (WMS) layers. These are published on the intranet using an OpenLayers map which also draws in data from external sources such as Oxford Archaeology (project locations) and Getmapping (OS New Popular Edition). The same layers are also accessible to our desktop GIS applications. Being entirely open source solutions, the main investment in this approach has been the time taken to learn the various components; the learning curve being pretty steep!

This investment in technical skills now allows us to offer specialist services to help clients get the most out of open source web mapping solutions, specialist skills being essential to make the most of the technologies. This is where platforms which allow non-specialist users to get involved are rapidly becoming the next big thing; more on this later.

Computing

Lasers and Light

Tom Goskar — Mon, 06 Oct 2008 15:57:59 +0000

Wessex Archaeology were asked to contribute an animation to the new touring version of last year's successful Making History exhibition, organised by the Society of Antiquaries of London. Over the next year, Making History will visit Salisbury, Stoke on Trent, Sunderland, and Lincoln. The exhibition will change at each venue to incorporate aspects of each region's own unique heritage.

Our animation, on show in Salisbury and South Wiltshire Museum until 3rd January 2009 (and at the end of this post!), gave us the opportunity to show some more of our work with the wonderful Stonehenge LiDAR dataset, as well as 3D laser scans of the Amesbury Archer's bones, and some new data captured with the University of Southampton's Archaeology department of WWI and WWII graffiti carved into trees on Salisbury Plain.

Lasers and Light from Wessex Archaeology on Vimeo.

LiDAR uses laser survey equipment mounted in an aeroplane to record the surface of the land below in three dimensions. The animation focuses on a field system in the Stonehenge World Heritage Site. Barely visible on the ground and in aerial photography, the features of the field system are revealed when a low level light is applied to the virtual landscape, throwing the virtual landscape into relief. The light source circles the earthworks, so their extent can be seen from all angles

Lasers can also be used on a smaller scale to study objects in greater detail. Here the skull and some of the long bones from the Amesbury Archer have been scanned. The 3D model has sub-millimetre accuracy, and can be used to study and measure their physical aspects without the need to touch the original.

3D laser scanning has also been used to record graffiti on a tree trunk on Salisbury plain on which the names of soldiers stationed there during training for both World Wars. Since they were carved the tree has grown, the bark expanded and the names have become harder to read. This visualisation shows how 3D data may be able to enhance the carvings and read the names more clearly, preserving them for the future. It may be possible to correlate the information on some of the trees with military records including dates of deployment on Salisbury Plain and the fate of the soldiers who carved their names.

We are very grateful to the Environment Agency for permission to use the LiDAR dataset from Stonehenge, and to Gareth Beale and Graeme Earl from the Archaeological Computing Research Group at the University of Southampton for processing the tree graffiti data during a hectic run-up to a season of excavations in Italy.

Find out more about our 3D laser scanning services.

Computing

LiDAR in Archaeology

Paul Cripps — Fri, 06 Jun 2008 00:00:00 +0000

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

Computing

The Stonehenge Landscape in 3D

Tom Goskar — Thu, 15 Nov 2007 00:00:00 +0000

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 (720p) 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.

An often asked question about the animation is about why the landscape is a neutral colour rather than a photorealistic texture. This is because we need to see the underlying form of the ground and natural colour can detract from what we are interested in seeing: the subtle features where people once 'worked' the ground into burial mounds, pathways, fields, etc. It is because many archaeological features are hard to see on the ground in normal daylight that we do the reverse (unusual lighting positions on a non-naturalistic textured landscape) to see the shadows and highlights of the earthworks themselves.

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.

Read more about Wessex Archaeology's work in and around the Stonehenge World Heritage Site, and view a zoomable version of the LiDAR. Find out more about the Stonehenge WHS LiDAR dataset on the English Heritage website.

A Virtual Stonehenge Landscape from Wessex Archaeology on Vimeo.

Computing

Surveying with SmartNet

Chris Brayne — Mon, 04 Sep 2006 00:00:00 +0000

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 SmartNet 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 SmartNet. This is a very cost effective upgrade which gives the older equipment a very productive new lease of life.

Computing

Well, hello world!

Chris Brayne — Wed, 05 Apr 2006 00:00:00 +0000

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.

Computing