Tag Archives: Laser Scanning

Wells Tracing Floor (eCAADe 2020)

In September 2020 we were due to visit Berlin to attend the eCAADe conference, however, COVID-19 shifted proceedings online. Our paper, written by the entire project team, documented and analysed the Medieval tracing floor at Wells cathedral using photogrammetry, reflectance transformation imaging and laser scanning. We presented a summary of our findings via a pre-recorded video and written paper. You can find links to these below, as well the paper abstract. We look forward to attending eCAADe and other conferences in person again once it’s safe to do so.

Documentation and analysis of a medieval tracing floor using photogrammetry, reflectance transformation imaging and laser scanning

Paper link

Video link

Abstract

The fifteenth-century tracing floor at Wells cathedral is an extremely rare survival in European architecture. Located in the roof space above the north porch, this plaster floor was used as a drawing and design tool by medieval masons, the lines and arcs inscribed into its surface enabling them to explore their ideas on a 1:1 scale. Many of these marks are difficult to see with the naked eye and existing studies of its geometry are reliant on manual retracing of its lines. This paper showcases the potential of digital surveying and analytical tools, namely photogrammetry, reflectance transformation imaging (RTI) and laser scanning, to extend our knowledge of the tracing floor and its use in the cathedral. It begins by comparing the recording processes and outputs of all three techniques, followed by a description of the digital retracing of the tracing floor to highlight lines and arcs on the surface. Finally, it compares these with digital surveys of the architecture of the cathedral cloister.

Back to Wells

Last week (11-14th October) we returned to Wells, revisiting our earlier scans and taking the opportunity to scan new areas. In particular, we have been privileged to be allowed to record the ‘tracing floor’, an extraordinarily rare survival of the ‘drawing office’ where the master mason worked out designs full scale by inscribing them on a plaster floor. The tracing floor at Wells is above the north porch of the nave, accessible from the triforium gallery via a spiral staircase in the north transept. Because the surviving examples are in fairly inaccessible places, it is believed that such spaces were probably used for design rather than for cutting stones, however it could be that more accessible multifunctional spaces may not have survived and that the ones we know about were exceptional. There is a larger and more famous example of a tracing floor above the north transept at York Minster, but the Wells example is of particular interest to us because it has been suggested (Pacey) that one area corresponds to the vaults of the cloister.

In recording the tracing floor we have decided to experiment with three different methods. Firstly, we have used photogrammetry, a method we have tested elsewhere, which is based on taking multiple photographs and stitching them together digitally to create an image without the distortion of perspective. We have also scanned the area using our laser scanner on its highest settings, to see how much detail it can record. Finally, we have used an innovative method called ‘RTI’ (Reflectance Transform Imaging). Like photogrammetry, this involves taking multiple images, however, reflective spheres are added to the scene and photographs are taken at intervals around the target’s hemisphere using a flash gun which is set at the same distance from the target in all images. These images are then processed using CHI software, which allows us to re-light the tracing floor from any angle and potentially reveals surface detials that have not previously been seen by eye. Our technicians, Sarah Duffy and JR Peterson, are experts in the use of this method and initial results look very promising in terms of picking up very fine levels of detail. However the method has disadvantages in that it can only currently be used successfully on small areas, which need to have a wide margin around them and which cannot yet be ‘stitched together’ to create a single image. We cannot therefore use RTI on the whole floor, except in individual sections towards the centre of the space. We have therefore sampled two areas that offer potentially interesting data: one which appears to show the springing off a vault and another which has some very fine details not recorded in previous surveys.

We have also taken the opportunity to take laser scans in colour, rather than the black and white we previously used, and to scan some areas we originally omitted, including the chapter house and the cloister. It has also been very helpful to re-examine areas where our data was of insufficiently high quality to answer more archaeological questions. We are very grateful to Jez Fry, the cathedral’s Clerk of Works, for granting us access and facilitating our studies at this most beautiful and fascinating building.

 

IJoAC Article

Our article investigating the use of digital generative design tools to assist with analysis of Exeter cathedral has now been published in  the International Journal of Architectural Computing.  This article can be viewed here – please contact us for further information. Abstract below:

Medieval masons relied on a ruler and compass to generate designs of increasing complexity in both two and three dimensions. They understood that arcs and lines could be used for proportioning, working with halves, thirds, fifths and so on, rather than specific dimensions. Geometric rules enabled them to create vaulted bays, high up in church and cathedral interiors. In recent years, the influence of digital generative design tools can be seen in our built environment. We will explore generative design to reverse engineer and better understand the design and computational processes that the medieval masons might have employed at our case study site of Exeter Cathedral, England. Our focus is on a run of bays along the nave, which at first appear consistent in their design, yet in reality are subtly different. We will investigate the capacity for changes in the generative process while preserving the overall medieval design concept.

Webb, N., & Buchanan, A. (2019). ‘Digitally aided analysis of medieval vaults in an English cathedral, using generative design tools’, International Journal of Architectural Computing, July 2019.

Fire at Notre-Dame

We were shocked and saddened at the scenes from Paris as Notre-Dame Cathedral blazed in the night. Today’s news that the structure of the building seems to be safe has come as a great relief, given its importance both as a symbol and as a monument of Gothic architecture.

The word-famous cathedral was started in around 1160 and the west front dates from the early years of the thirteenth century. Later in that century, the upper storeys were remodelled to introduce a larger clerestory with traceried windows and the transept facades, with their celebrated rose windows, were added. As the mother church of Paris, the building has undergone many alterations and additions over its history, most significantly at the Revolution, when religious images were attacked, and in the nineteenth century, when architect Viollet-le-Duc undertook a major restoration, including the rebuilding of the wooden spire whose dramatic fall became one of the defining moments of the inferno.

Thoughts are already turning to the possibility of reconstruction, to which President Macron has stated his commitment and many millions of euros have been pledged from around the world. This is where research such as ours can be particularly valuable. Thanks to years of surveying and a recent laser survey by the late Professor Andrew Tallon, Notre-Dame is probably one of the best documented medieval buildings in the world. The level of detail provided by a laser scan, consisting of millions of digital points recorded in space to create an exact 3-D digital model, could enable a reconstruction to produce a stone-by-stone replica of a destroyed building. That is not to say that laser scanning would provide all the answers: scans can only record what is visible and cannot identify what is going on under the skin of the building. In particular, wooden roofs of the kind that has been destroyed at Notre-Dame are particularly difficult to document by digital means. Nevertheless, laser scan data would make it relatively easy to interrogate the geometries of the parts of the vaulting that have been lost, in order to accurately recreate their three-dimensional form. The geometries used would thus be based on an understanding of the design methods originally used by the medieval masons. There is a wealth of expertise that the reconstruction team could draw upon to assist in this work, with researchers in Spain, Germany and the United States (as well as us in the UK) all using digital techniques for documentation, interrogation and reconstruction purposes.

Paradoxically, it has often been the case that disasters have helped to enhance our understanding of buildings. The nineteenth-century architectural writer, Robert Willis, who has inspired our research, explored the debris surviving after the collapse of one of the western towers of Canterbury Cathedral and found a stone from the fourteenth-century vault still inscribed with the setting-out lines used by the masons when cutting the vault ribs. He used this as evidence for understanding how their designs were projected into three dimensions. Viollet-le-Duc used his experience of very thoroughgoing restorations to draw conclusions about medieval vaulting techniques, including at Notre-Dame. Some of his theories about the structural behaviour of vaults were challenged by the destruction of some of the northern French cathedrals during the First World War: at times the ribs collapsed, leaving the webbing, supposedly supported by the ribs, still standing without them. It may be hoped that the damages at Notre-Dame might be equally enlightening for further research on early Gothic vaulting, which can then inform the rebuilding.

Victor Hugo, whose 1831 novel Notre-Dame de Paris (more famous in English as The Hunchback of Notre-Dame) called for the restoration of the cathedral, spoke of three agents of change: time, revolution and fashion. To this should be added disaster. He understood all works of architecture as social products, the sediments of ages – as he put it ‘Time is the architect; the nation is the mason’. The future reconstruction of Notre-Dame should be seen in this light. It cannot return Notre-Dame to how it was before the fire, still less to any ‘original’ medieval state. Indeed, even if timber on an adequate scale were available it could be questioned whether there is value in replicating a less visible part of the building whose significance lay in the original timber and medieval carpentry techniques. Nevertheless the reconstruction work of the twenty-first century, which will doubtless use both traditional skills and cutting-edge technologies, will form the latest chapter in the biography of this beautiful building.

Image credit: Antoninnnnn

6ICCH Presentation

 

In July we attended the 6th International Congress on Construction History, hosted in Brussels, Belgium. The conference included participants with a wide range of interests in construction history and there was a strong showing of researchers investigating vault design and construction. This included colleagues from Spain and Germany, such as David Wendland and Marie Jose Ventas Sierra’s  talk on the Hall of Arms vault in Albrechtsburg Meissen as well as Rocio Maira Vidal who discussed the abandonment of sexpartite vaults across Europe, including Lincoln Cathedral in England. It was a delight to meet Jacques Heyman, who wrote ‘The Stone Skeleton’, and gave a fascinating talk on the change of level in the fan vaults at Kings College, Cambridge.

At the congress we shared our initial investigations of the nave and choir vaults at Exeter cathedral, which we surveyed in 2016. We suggest that all the high vaults were laid out in two dimensions using a geometrical figure called the ‘starcut’, allowing the same proportions to be maintained throughout, despite different bay dimensions. The three-dimensional geometry of the vaults, however, presents significant variation between bays. These appear to correspond with the construction sequences proposed by previous scholarship. Nevertheless, the nature of the variations does not correspond fully with previous interpretations. We propose that two-centred arcs were found at Exeter earlier than generally recognised and in a different pattern of distribution than previously suggested.

More information on 6ICCH can be found here.

The Architecture and Archaeology of Ely: Papers in memory of Anne Holton-Krayenbuh

We were delighted to have the opportunity to present our initial findings on the tracing floor processes of the 14th century vaults at Ely cathedral as part of the Cambridge Antiquarian Society’s day investigating the Architecture and Archaeology of Ely, in memory of Anne Holton-Krayenbuh. We discussed our work to date on the medieval vault designs of Bishop Hotham’s choir vaults, both in the main vessel as well as the north aisle, and the particular research problems we’ve faced compared to other sites of investigation given that we appear to have uneven impost levels across vault bays.

 

It was excellent to hear from the other speakers at the event, starting with Dr Catherine Hills discussing the clothing and jewellery discovered at local burial sites during the time of Etheldreda. Next, Ely cathedral archaeologist Dr Roland Harris presenting an overview of the Romanesque parts of the cathedral, and we are keen to share our survey data with Roland to assist in future building work. Rebecca Lane from Historic England then presented findings based on surveys of Ely’s early urban buildings, which surprisingly included a tierceron vault in the cellar of one of the high street shops. Dr John Maddison gave an excellent talk on Bishop Hotham’s tomb in the cathedral, and the possible solution of it now being two separate pieces. Elizabeth Stazicker, the cathedral archivist, then concluded with a talk highlighting a few of the fascinating artefacts in her custody, as well as reminiscing on her time with Anne Holton-Krayenbuh.

 

It was an insightful and stimulating day, and we were very grateful for the opportunity to be part of it. We look forward to future events organised by the Cambridge Antiquarian Society, where we can hopefully return in future once our research progresses.

 

The Architecture and Archaeology of Ely: Papers in memory of Anne Holton-Krayenbuh was held at The Maltings in Ely on 10th March 2018.

British Art Studies Article

Our article investigating the creativity and imagination used to design the choir aisles at Wells cathedral has now been published in ‘British Art Studies’.  This article is free to view here.

Abstract

This paper explores the topics of creativity and imagination in relation to the design and construction of the lierne vaults in the presbytery aisles of Wells Cathedral, erected around 1330. It explores the potential of digital scanning and analysis for forensic investigation of the structure in order to identify the processes involved. Four different processes were employed and we compare those used in the three eastern bays of the north and south aisles. These are shown to share characteristics with the retrochoir but to involve different approaches to 3-D projection and stone-cutting. We conclude that the basic geometry of the vaults was defined in advance of construction, using full-scale drawings worked out on a tracing floor. In both sets of vaults the 3-D geometry continued as a sequence of steps and was derived from measurements ascertained from existing elements (including the drawings) but was not consistent across the two aisles. The processes reveal different priorities, whether for level ridges (north aisle), different choices in terms of rib radii or apex heights, and different sequences of design steps. This demonstrates the potential for experimentation at every stage of construction.

Buchanan, A., & Webb, N. (2017). ‘Creativity in Three Dimensions: An Investigation of the Presbytery Aisles of Wells Cathedral’, British Art Studies, Issue 6.

Scanning at Tewkesbury and Gloucester

In July 2017, we travelled to Tewkesbury Abbey and Gloucester Cathedral to create digital surveys of their respective vaults. First, we surveyed the abbey at Tewkesbury using our standard methods of laser scanning and photogrammetry, with the additional method of total station for the choir vaults. Total station surveying enables us to manually capture specific points of the vault ribs, as opposed to laser scanning which captures all points. Searching for specific points to document using total station is very labour intensive, particularly when trying to capture the vaults above. Based on advice from our friend David Wendland, who is carrying out exciting research on vaults in continental Europe, we worked in a pair with one of us roughly locating points using the total station’s laser, and the other laying on the floor looking up at the vaults through a pair of binoculars to locate the precise point that needed to be documented. This was a particularly long and arduous task over a day and a half, however, the resulting points mean we can very quickly and efficiently use the specific points documented to trace the vault rib geometries. Laser scanning, on the other hand, is much more time consuming in locating the required points amongst many million others to trace them. Both methods create accurate results and therefore having two sets of data ensures an even higher level of confidence in our methodology and findings. Once we completed our surveying, we backed up our data and travelled to Gloucester Cathedral to start the second phase of our field trip. We also found time in between to visit Pershore Abbey, where we already have access to a laser scan survey to investigate the vault geometries there. This scan data was very generously given to us to use by the abbey to use for our research, and we hope to be able to show are results of this in the next year. The Pershore Abbey laser scanning was particularly high in its quality, surveyed by CGD Ltd.

At Gloucester we continued with our primary method of laser scanning to survey the majority of the cathedral’s vaults, with particular attention given to the west end, transepts, crossing, choir and presbytery vault bays. Whilst at Gloucester, we were able to use our scan data to assist the cathedral architects in the installation of a new disabled platform to the east end as part of HLF funded Project Pilgrim, by linking scans from the crypt to those above to build up a very detailed picture of how the spaces connect, which was previously not accurate enough. This demonstrates how our survey data can be used by other stakeholders for mutual gain.

We are very grateful for the Liverpool School of Architecture’s David Foster Wicks endowment fund, which funded the field work and has enabled us to continue developing our research for Tracing the Past.

DAACH Article

Our article investigating the use of digital techniques to analyse the choir aisles at Wells cathedral has now been published in ‘Digital Applications in Archaeology and Cultural Heritage’. This article is free to view until 7th May 2017 through the following link:

https://authors.elsevier.com/a/1UkLO7szebZ9pb

Abstract

Architectural historians have identified Wells cathedral as a key monument in the transition between high and late Gothic, a move in part characterised by the rejection of simple quadripartite or tierceron rib vaults for more complex vaults. Here we will show how digital methods are used to reopen questions of design and construction first posed in 1841 by pioneer architectural historian Robert Willis. Digital laser scanning documents vaults accurately, thereby establishing their geometries to a high degree of certainty and, at Wells, highlighting differences between the choir aisle bays which have previously been treated as a single design. Significantly, we will show how digital techniques can be used to investigate these differences further, using point cloud data as a starting point for analysis rather than an end point. Thus we will demonstrate how modern technologies have the potential to reignite historic debates and transform scholarly enquiries.

Webb, N., & Buchanan, A. (2017). ‘Tracing the past: A digital analysis of Wells cathedral choir aisle vaults’, Digit. Appl. Archaeol. Cult. Herit., 4, March 2017, pp. 19–27.

Digital Past 2017

This week Nick presented at Digital Past 2017 in Newport, Wales. The paper focussed on the digital surveying and subsequent analysis of the fourteenth century medieval vaults  in the chancel and north transept of Nantwich St Mary’s Church, Cheshire. This produced two distinct discussions; the first investigating the chancel, which offered an opportunity to hypothesise the medieval design process of the in-situ vaults using reverse engineering. The second, the north transept, contains an incomplete (or possibly destroyed) vault and therefore a series of simulations were developed to postulate the design process, and how the vaults may have looked if completed. 3D digital models of the postulated designs for the north transept can be found on the Nantwich vaults page.

The conference presented numerous exciting and innovative digital heritage projects in Wales and beyond, such as Nick Hannon’s investigations into the Antonine Wall, as well as the Welsh Chapels project which is using games engines as a way of educating the public about heritage.