Paul Cripps's blog

3D Laser Scanning for HeritageOriginally published in 2007, the new 2011 revision (2nd edition) of 3D Laser Scanning for Heritage has been published by English Heritage. It is available to download as a PDF from their website (other formats may also be requested). Once again this key guidance document has been published under the aegis of Heritage3D.

Wessex Archaeology are pleased to have supplied three case studies to the 2nd edition: Tamworth Castle, Sandsfoot Castle and Wakehurst Place.

For more information about our geomatics services, please see our geomatics pages; there is an ever growing list of case studies and more information about our techniques such as Terrestrial Laser Scanning (TLS).

The churchyard of St George's church, Portland

Wessex Archaeology have been commissioned by the Churches Conservation Trust (CCT) to undertake survey work at St George's church, Portland. The church is described by CCT as:

Vast and solitary, St George's is one of  the most magnificent 18th-century churches in Dorset. It rises from the rocky, treeless and dramatic peninsula of Portland and is the masterwork of a local mason named Thomas Gilbert who supplied the Portland stone used to build St Paul’s Cathedral.

We have just posted some new and interesting case studies as well as more information about techniques we use to satisfy the demanding needs of heritage survey & GIS projects.

As recently announced, Wessex Archaeology have been accepted as Affiliate Members of the Survey Association.  We provide a range of geomatics services for the heritage sector and our TSA membership will help us to develop these services further.

Working closely with hardware and software manufacturers, academic institutions and partners in the survey industry, as well as our own in-house teams of archaeological surveyors and geomatics experts, built heritage and archaeology specialists, we provide tailored solutions for all manner of projects.

These range from small scale recording of architectural features or buildings as part of planning applications right through to detailed surveys of entire building complexes or landscapes as part of planning proposals, mitigation of works, research grant proposals, Environmental Impact Assessments or Heritage Lottery Fund bids.

Recently, we have been busy with a wide variety of survey projects as well as supporting the Stonehenge and Avebury Research Framework project.

Find out more about our archaeology geomatics services.

Wessex Archaeology have been using digital survey instruments including Total Station Theodolites (TST) and Geographic Positioning System (GPS) survey instruments for many years now and they have allowed us to radically improve the efficiency with which we can set up and survey archaeological sites, monuments, landscapes and buildings.

Here is a brief history of survey instrumentation at WA from the very beginning to this latest development.

In the beginning...

There were tapes, theodolites, plane tables and dumpy levels. These tools and instruments have been around for centuries and whilst being tried and tested, they rely on the surveyors skill to record appropriately and process the measurements being taken. All in all, a time consuming process.

The Total Station Theodolite (TST or just TS) has been commonplace on archaeological projects for many years now and provides a robust, reliable, and importantly very accurate and precise way of recording spatial information in three-dimensions. It is basically a traditional theodolite for measuring angles combined with an electronic distance measure (EDM) and a computer/data logger for processing and storing the measurements. We use these for many tasks where accuracy and precision is of prime importance and also for recording upstanding structures and buildings.

Total Stations typically require two people to operate them: one person controlling the instrument itself and another holding a prism as a target for the laser used to measure distance. Our Leica 1200 series instruments which we have been using for a number of years now are fully robotic with remote control via radio; this means a single person can operate the instrument with the controller mounted on the prism staff and the instrument following the prism wherever the operator goes. They are also capable of operating in reflectorless mode, removing the need for a prism and allowing us to record measurements in places where it would otherwise not be possible such as high up on the elevations of buildings. They can also interface directly with Computer Aided Design (CAD) systems running on portable tablet PCs so that we can record straight into digital 3D models.

Global Positioning Systems (GPS)

Our first GPS instruments were Leica 500 series GPS units which could be used to set up survey stations ready to survey with a TST. This meant survey data could be captured using the British National Grid coordinate system rather than by using a local grid coordinate system and converting coordinates back in the office by means of a surveyed ground marker of known location such as a benchmark or trig point. We still use this approach where we need to set up TS stations where there is no other form of control.

Another way of the using the instruments is to use two in a setup called differential GPS or dGPS where one instrument is set up in a fixed location (the base station) which then provides live correction signals via radio to another instrument (the rover). This allows the rover to survey with improved positional accuracy and precision than if it was used on its own without the correction signals. To improve quality of measurement still further, the survey data can be processed back in the office against data recorded by one or more fixed base-stations maintained by the Ordnance Survey. Importantly, using dGPS in this way is far more efficient for many survey tasks as, unlike with a TS, there is no need for lines of sight across the site; as long as the instruments can see enough satellites and are within radio range, the surveyor can survey anywhere they like.

More recently we have been operating a fleet of Leica 1200 series instruments which have a number of technological advances over the older 500 series. The 1200 series instruments are smaller and lighter, use less power (so have smaller batteries), have improved antennae and are generally easier to use in the field. One version of the 1200 series which we used was entirely pole mounted, equivalent in use to the prism pole used with a TS but without the TS.

The smart solution

The biggest change to date came with the advent of SmartNet. This is a collaboration between the Ordnance Survey and equipment manufacturers including Leica. SmartNet uses the mobile phone network to provide real-time correction signals from OSNet, the Ordnance Survey's correction signal network. This uses the location information from fixed base-stations located around the country. In other words, the need for a physical on-site base-station is removed; instead, a correction signal is fed straight to the rover instrument across the internet giving differential GPS with only one instrument. Using this system it is possible to go out to site and be surveying within minutes; simply set up the rover device, connect to the internet and go!

From GPS to GNSS

Another major change is the move from the US operated Global Positioning System (GPS) to the more generic Global Navigation Satellite System (GNSS) platform. These newer GNSS instruments can recieve signals not only from the US GPS satellite constellation but also the Russian GLONASS constellation, the Chinese COMPASS constellation and soon the European Galileo constellation.

This means more satellites visible to the device, improving the quality of the location measurement. Also,  these newer satellites broadcast stronger and improved signals, allowing GNSS instruments to operate reliably in places the older GPS only instruments will not work effectively such as near to buildings or trees.

Find out about Wessex Archaeology's new fleet of Leica Viva GNSS/SmartNet survey equipment.

Leica Viva SmartRover: One of our new Leica Viva SmartRover dGNSS instrumentsWessex Archaeology are pleased to announce the arrival of our brand new fleet of survey instruments from the Leica Viva range of Global Navigation Satellite Systems (GNSS).

These newer GNSS instruments can recieve signals not only from the United States GPS satellite constellation but also the Russian GLONASS constellation, the Chinese COMPASS constellation and soon the European Galileo constellation.

Our new Viva instruments are are all SmartNet enabled. This uses mobile phone networks to provide real-time correction signals from OSNet, the Ordnance Survey's correction signal network. This enables us to begin surveying on most sites within minutes.

We have also upgraded our Total Stations to use the new Viva controllers giving us a single platform for all of our survey instruments; this ensures commonality across the fleet with the same interfaces and data structures in operation irrespective of the instrument used.

The improved interface design and modular nature of the instruments allows us to build on our already highly efficient survey processes, keeping us at the cutting edge of archaeological survey techniques.

Work on the next version of our in-house survey processing software using the latest features available on the Viva instruments is also underway; this will further advance our on-site recording methodology and increase the ease with which we can use survey data in our post-excavation GIS and database based processes.

More information

For more information on our Geomatics services available to clients, see our Geomatics services page or contact Paul Cripps.

For more information on GNSS, see the Inside GNSS website.

For more information on real-time kinematic dGNSS systems in the UK see the OSNet website and Leica Smartnet website.

Web mapping has now been made even easier by the advent of platforms such as Google My Maps where it is possible to create layers from scratch or easily overlay any KML (Keyhole Markup Language) file or GeoRSS feed over Google Maps, all done through an easy to use web interface.

 A map of crime on the UK produced using the Maker! application at Geocommons.com A new site, Geocommons.com from FortiusOne, takes the concept of web mapping a step further by not only providing an online mapping application called Maker but also a spatial data library or warehouse complete with search tools called Finder. Together, Finder and Maker allow non-specialist users to quickly and easily load their own spatial data or find relevant data from the warehouse and then produce cartographically appealing maps in minutes. Data can be uploaded by registered users in simple table format for points or as shapefiles or KML for more complex geometry.

The Finder and data warehouse are an exciting development. For the first time, layers of geographic information can be uploaded and published using Creative Commons licensing. Tags are used to describe and find resources. A bit like Flickr, Scribd or YouTube but for spatial data rather than photos, documents or videos. Any data which is in the public domain is allowed to be uploaded with the onus firmly on the uploader to ensure any copyright or intellectual property conditions are met. With only this small caveat, any layer uploaded is instantly available to any registered user to create a map from. There are also enterprise options for business users to allow them to keep their data private, the aim here presumably being to make inroads into what has till now been the preserve of heavyweight desktop GIS applications.

The map Maker side of things provides the same kind of functionality as other online map creation tools but with the benefit of seamless integration with the Finder and everything being controlled through an intuitive graphical interface in the web browser. So any layer in the Finder can easily be added to a map and styled with only a few clicks with a choice of basemaps from Google Maps. In addition to simple maps showing locations of points of interest, lines or polygons with fairly basic symbology, Maker provides users with more advanced cartographic tools for producing thematic maps more akin to the sorts of thematic maps produced using desktop GIS but without the need for any in-depth background knowledge of GIS applications, programming, markup or anything complicated at all, everything being accomplished in the web browser interface. I managed to create a map showing levels of crime in the UK and one of antimony mining sites in only a few minutes (and the first thirty seconds of that was creating a user account!).

There are a couple of drawbacks however. The main problem in the UK which detracts from the ease of use is the lack of support for coordinate systems. As with the majority of online mapping tools, positions have to be recorded using global lat/lon coordinates. Whilst this makes it ideal for uploading data captured using GPS, many datasets here in the UK use a British National Grid projection, so publishing them using the Finder/Maker application requires that the coordinate system for the data must be transformed before the data is uploaded. As any GIS professional will tell you, this can be fraught with danger for novices and may require specialist software.

The fact that data in the Finder is only accessible to the Maker application or as a download is a bit restrictive; it would be nice to be able to access the layers as web-services to build into other applications. Or bring layers into Maker from other sources. Trying to do both the warehousing and mapping aspects may be great for performance but is not necessarily the best way forward; layer separation and keeping data separate from interface is way more flexible but I imagine completely impractical with todays infrastructure. Roll on web 3.0!

Of course, as with any such site based around user generated content, there will be some poor quality content and it will be necessary to be a bit discerning when choosing layers. I wasn't aware for example that the London borough of Brent has moved to the south-west, as indicated on the UK Crime map I produced using one of the layers from Finder. But in so far as providing a great set of tools for producing maps online quickly and easily and a very big warehouse in which we can put collections of geodata to be shared, it has to be a big well done to the folks at Geocommons.

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.

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