The Photogrammetric Record 19(106): 94–110 (June 2004) PHOTOGRAMMETRIC RECORDING OF THE ROMAN EARTHWORKS ‘‘CAWTHORN CAMPS’’, NORTH YORKSHIRE Jane L. Stone (jane.stone@english-heritage.org.uk) Michael Clowes (mick.clowes@english-heritage.org.uk) English Heritage (Based on a paper read at the one-day symposium of the Remote Sensing and Photogrammetry Society, entitled Architectural and Archaeological Recording, at English Heritage, York on 27th February 2003, together with the ensuing discussion) Abstract Cawthorn Camps is a Roman site of probable late 1st and early 2nd century date comprising two forts, one with a later annexe, and a camp. The site survives as earthworks and, within the main defences, there are many slight embanked structures. The current multidisciplinary programme of research has included geophysical prospection, excavation, ground and aerial survey; it is a joint initiative by the North York Moors National Park Authority and English Heritage. The project aims to increase academic understanding, improve information available to the public and assist the production of a revised management plan for this nationally important site. Large-scale air photographs and digital photogrammetry have been used to produce a plan, at scale 1:500, of the earthworks to a precision of ±10 cm. This plan has been used as a base map with which to rectify other key photographs and plans allowing further detailed interpretation and mapping to be undertaken. The air photographic work has also investigated some of the products available through digital photogrammetric technology, such as digital elevation models (DEMs), orthophotographs and perspective views. Keywords: air photographs, Cawthorn Camps, digital photogrammetry, earthworks, hachured plan, Roman forts and camp Introduction Cawthorn Camps is an important scheduled earthwork site of largely Roman date situated on the southern edge of the North York Moors within the area of the North York Moors National Park, North Yorkshire (Fig. 1). The site is located on the edge of an east– west escarpment commanding excellent views over moorland to the north and, prior to the growth of surrounding woodland, the Vale of Pickering to the south. As illustrated on
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. Blackwell Publishing Ltd. 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street Malden, MA 02148, USA. The Photogrammetric Record Fig. 1. Cawthorn Camps location map and oblique aerial photograph. (Photo reference: NMR SE 7890/19. 7th May 1993.
Crown copyright. NMR). Fig. 1, it comprises, from west to east, a fort, D, an unusual coffin-shaped camp, C, and a second fort, A, with a later adjoining annexe, B. The site covers approximately 15Æ5 ha, with maximum overall dimensions of 720 m by 290 m. A reputed medieval trackway, the Portergate, runs through three of the four earthworks. Within the interiors of the earthworks, in particular Camp C, Fort A and Annexe B, there are numerous embanked structures. There is also evidence of pre- and post-Roman activity on site. In the 1920s the site, in particular Fort A and Annexe B, was extensively excavated by F. G. Simpson (Simpson, 1926) and Sir I. A. Richmond (Richmond, 1932). Much of what is known about the site is a consequence of this work and many of the trenches and spoil heaps resulting from those excavations are still visible today. More recently, in 1976, the earthworks were comprehensively surveyed at a scale of 1:1250 by the Royal Commission on the Historical Monuments of England (RCHME). This plan was updated by the RCHME in 1992 for a book about Roman camps (Welfare and Swan, 1995, pp. 137–142). The current programme of research at Cawthorn is a joint initiative funded by English Heritage and the North York Moors National Park Authority, the main aims being to improve academic understanding, information available to the public, and also to produce a revised management plan for this nationally important site (Wilson and Lee, 2000a, pp. 29–32). In addition, it has provided an ideal opportunity to investigate
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. 95 Stone and Clowes. Photogrammetric recording of the Roman earthworks ‘‘Cawthorn Camps’’ new methods and technology and to combine the results of various areas of research. It has been a multidisciplinary project combining geophysical, field and aerial survey, along with two seasons of excavation. The magnetic geophysical survey, carried out in August 1999, investigated two sample areas—one in Fort D and the other in Annexe B. Conditions for the survey were not ideal due to uneven ground conditions and dense moorland vegetation. Both areas proved to be of low magnetic susceptibility and the majority of the weak anomalies detected are thought to represent glacial features (Wilson and Lee, 2000a, appendix 11). A detailed, ground-based earthwork survey (scale 1:200) was undertaken by Ed Dennison Archaeological Services (Dennison, 1998) for the southern part of Annexe B, the area of the best preserved internal structures. The survey was subsequently extended to incorporate the rest of Annexe B and Fort A. The excavations were undertaken in two seasons in 1999 and 2000 (Wilson et al., 2003). A total of 10 trenches were opened, selected to investigate not only the character and date of the earthworks but also other issues, including the impact of visitor erosion and agriculture on the complex. The results of these excavations confirmed the 1st and 2nd century ad dating for the majority of the site, as proposed by Richmond. Turf structures examined in Fort A and Annexe B were shown to represent buildings associated with the Roman military occupation. Additionally, the presence of pre- and post-Roman activity on site was demonstrated. Two features of prehistoric date were discovered underlying the rampart in the north-west corner of Fort A, and a feature, previously excavated by Richmond, dug into the eastern rampart of Fort A, proved to be a sunken-featured building of early medieval date. However, the aim of this paper is to give an overview of the air photographic work. This has comprised two main phases. In the first phase, photogrammetry, using air photographs, was undertaken to produce a metrically accurate plan of the earthworks (Bewley, 2003, pp. 282–284; Stone, 2003). In the second phase, the resulting plan was used as a base map with which to rectify other key air photographs and plans enabling further detailed interpretation and mapping. An attempt was made not only to identify and interpret the multi-period archaeology at Cawthorn but also to locate as many of the 1920s excavation remains as possible. A report (Stone, 2002) detailing the results of both phases of the air photographic work is available through the English Heritage National Monuments Record archive in Swindon (National Monuments Record Centre, Kemble Drive, Swindon SN2 2GZ, UK, http://www. english-heritage.org.uk). Phase I—Digital Photogrammetry The photogrammetric plotting of the earthworks at Cawthorn was achieved through a collaboration between the Aerial Survey and Metric Survey sections of English Heritage, combining the interpretative skills of the former with the technological expertise of the latter. The English Heritage Archaeological Investigation section also helped with the capture of ground control using the global positioning system (GPS). The use of photogrammetry to plot earthworks in England has a long history. Over the last 20 years the Aerial Survey section of the former RCHME, now English Heritage, has undertaken a number of photogrammetric projects to record upstanding archaeological remains. These include landscape surveys such as Bodmin Moor, 96
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. The Photogrammetric Record published in 1994 (Johnson and Rose, 1994). Moreover, the English Heritage Metric Survey team has used photogrammetry for nearly 30 years to record structures and buildings to great levels of accuracy (Bryan and Blake, 2000). However, this is the first time English Heritage has undertaken a photogrammetric project targeted at recording earthworks to this scale and level of accuracy. It is the following factors which have set the Cawthorn project apart from what has gone before. Firstly, unlike previous projects, the colour air photographs taken for Cawthorn were specially commissioned at particularly large scale (1:1600) and were taken with a Zeiss RMK TOP aerial camera with a 12 inch (305 mm) focal length and forward motion compensation. A total of 16 photographs were taken in two strips, each comprising 8 photographs, splitting the site into north and south. They were taken with a 60% forward (east–west) overlap and a 25% lateral (north–south) overlap, ensuring total stereoscopic coverage for the survey area. The film diapositives were scanned at 25 lm resolution using a photogrammetric scanner giving a pixel ground sample distance (GSD) of approximately 4 cm. Secondly, the 20 ground control points used to georeference the photographs were established using the Trimble dual frequency GPS to an accuracy of ±12 mm. These were distributed throughout the survey area to provide a sound framework for the aerial triangulation. Features used for control, visible on both the photographs and the ground, ranged from hummocks of vegetation to fallen timber and pieces of stone. The size of the features that were used as control is an indication of the level of detail that was visible on the photographs. Thirdly, the project has used the latest digital photogrammetric technology, a Leica Helava Systems photogrammetric workstation running SOCET SET software. The triangulation of the two strips was carried out manually using the Multi-Sensor Triangulation module. Following the bundle adjustment, the XYZ rms errors for the control points were 0Æ042, 0Æ038 and 0Æ024 m, respectively, the maximum error at any one point being 0Æ087 m in X. The 3D stereomodels from which plotting was undertaken were viewed on the workstation monitor using polarising glasses. The vector details of the earthworks and other archaeological features were captured using PRO600 and MicroStation. Fig. 2(a) is the resulting photogrammetric plan which took 35 days to produce. The line detail depicts the tops and bottoms of earthworks and the colour-coded layers represent different categories of feature. Following additional interpretation and mapping from other key photographs and plans, the photogrammetric plan was worked up into the finished hachured drawing (Fig. 2(b)). When the project began, it was uncertain how much of the earthwork detail would be visible on the photogrammetric stereomodels, especially considering the nature of the rough moorland vegetation at Cawthorn, which effectively masks features. The results of the plotting have far exceeded initial expectations. Not only have the main defensive earthworks been mapped, but also many slight internal features, including banks of only 10 cm in height. New features have been identified along with further detail for already known features. Comparison of the air photograph plan to the field survey produced by Dennison (1998) for Annexe B at scale 1:200 shows a close correlation of features recorded. However, there are gaps in the plan where the full extent of the earthworks could not be seen due to tree cover and heavy shadow. One of the benefits of digital photogrammetry is the ability to manipulate the scanned imagery to provide further products. For example, the software can generate digital elevation models (DEMs) and orthophotographs. An orthophoto is an image
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. 97 Stone and Clowes. Photogrammetric recording of the Roman earthworks ‘‘Cawthorn Camps’’ Fig. 2. (a). Extract of vectorised line detail, reduced from the original at 1:500 scale, of the earthworks at Cawthorn plotted from the digital photogrammetric stereomodels. An indication of the overall size of the monument can be gained from the rectified and scaled images in Fig. 8.
English Heritage. NMR. (b). Extract of final hachured plan of the earthworks, reduced from the original at 1:500 scale, representing a combination of the highly accurate photogrammetric plot supplemented by information from other key photographs and plans. Features in red are well-preserved earthworks; less well-preserved earthworks are depicted in green; blue features represent trenches and spoil heaps resulting from the 1920s excavations; yellow features were mapped from photographs taken in 1993; the two numbered magenta rectangles represent the location of trenches opened in 1999–2000.
English Heritage. NMR. 98
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. The Photogrammetric Record which has had the scaling errors caused by tilt and depth variation inherent in the photography removed, in effect producing a true-scale, plan view of the subject. A DEM is first required in order to determine the ground surface and then the software resamples the digital imagery, re-scaling as necessary to produce the orthophoto. Fig. 3 is an orthophoto of Cawthorn produced from a mosaic of 12 air photographs; it is based on an elevation model, created automatically by the software, formed by a grid of points at 1 m spacing and comprising a total of 1Æ13 million points. This, and all the other elevation models mentioned below, were created automatically by the software and consist of a grid of points of selected spacing; no additional breaklines were included in the models, nor was any manual editing of them undertaken. In addition, a trial was undertaken to see whether a denser elevation model would succeed in indicating the subtle embanked features within the main defensive earthworks. The red rectangle on Fig. 3 defines the first test area in Annexe B which incorporated the line of the rampart to the south as well as some internal features. Fig. 4(a) is the orthophotograph of this extract. Fig. 4(b) shows the orthophoto again, overlaid with a grid elevation model taken at 0Æ5 m intervals, and illustrated as contours. The lines of low interior banks, some only 20–30 cm in height, are clearly identifiable; these represent the remains of turf-built structures of probable Roman date. Fig. 3. Orthophotograph of Cawthorn Camps (GSD 0Æ2 m). The red rectangle shows the location of the extract illustrated in Fig. 4.
English Heritage. NMR.
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. 99 Stone and Clowes. Photogrammetric recording of the Roman earthworks ‘‘Cawthorn Camps’’ Fig. 4. Extract from Annexe B including orthophotograph, GSD 0Æ1 m (a); orthophotograph overlaid with height information (b); and two grey scale perspective views (c) and (d).
English Heritage. NMR. The software can also generate perspective views of the subject from different angles; this process also drapes the aerial imagery over the elevation model. Significantly, lighting and colour balance can also be changed. Fig. 4(c) illustrates a view of the extract from Annexe B taken at a near vertical angle and changed to grey scale; the direction of sunlight was changed to come from low in the sky from the northeast in order to highlight the subtle earthworks to better advantage. Removal of the differing colours of vegetation also makes the earthworks more clearly visible. Lighting is a critical factor in the identification of earthworks both in the field and on photography, so the ability to change it digitally has great potential for the interpretation process. Similar experiments were done for Fort D (Fig. 5), Camp C (Fig. 6), and Fort A and Annexe B. All these images were based on a grid elevation model of 1 m spacing. The perspective view of the south-east quarter of Fort A illustrated in Fig. 7 was based on an elevation model of 25 cm spacing. The level of detail visible is considerable, for example, lines of vegetation defining the edges of one of the back-filled excavation trenches opened in 1999 can clearly be seen. The work at Cawthorn has not only shown the potential of using digital photogrammetry for the large-scale mapping of earthwork sites, it has also gone some 100
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. The Photogrammetric Record Fig. 5. Orthophotograph of Fort D, GSD 0Æ1 m (a); and two grey scale perspective views (b) and (c).
English Heritage. NMR. way to demonstrating the variety of products (elevation models, orthophotographs, perspective views) that can be generated through the photogrammetric software. These are not only useful for informing the interpretation process, but also have great potential in terms of presenting the site to others, making the archaeological and topographical information more understandable. The conventional form of depicting earthworks through hachured plans is sometimes not easy to understand for those who do not have a specialist knowledge. Furthermore, it is perhaps important to note that although the plan itself is created through an interpretation of the earthworks, so will always be subjective to some extent, the photographs give a totally objective record of the site at the point in time when they were taken and can be re-examined for further information and re-interpretation as necessary. Phase II—Single Photo Rectification In the second phase of the air photographic work other historic and more recent oblique and vertical photographs and plans (see Tables I–III) were rectified or aligned with the photogrammetric plan and further detailed interpretation and mapping of features undertaken. The rectifications were done through the AERIAL 5Æ18 Air Photograph Rectification software developed by John Haigh of Bradford University (Haigh, 1996). The photogrammetric plan was used as control for all the rectifications; some used a simple plane transformation but the majority incorporated basic elevation
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. 101 Stone and Clowes. Photogrammetric recording of the Roman earthworks ‘‘Cawthorn Camps’’ Fig. 6. Orthophotograph of Camp C, GSD 0Æ1 m (a); and two grey scale perspective views (b) and (c).
English Heritage. NMR. models produced by the photogrammetric software. This allowed the AERIAL 5Æ18 program to rectify using a 3D perspective transformation algorithm. The results were good with an accuracy for most of the rectifications in the sub-metre range. The photogrammetric plot and the rectified photographs were loaded into AutoCAD Map with Key Terra Firma software, where the additional mapping and final hachuring of the plan was undertaken. The photographs and plans which contributed further information include an OS map dating to 1912 which shows the area of the Camps almost totally afforested, with 102
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. The Photogrammetric Record Fig. 7. Grey scale, perspective view of the south-east quadrant of Fort A. The red arrow shows the location of one of the excavation trenches, trench 2, opened in 1999. The trench has been in-filled, but its edges, showing as heightened lines of vegetation, are clearly visible. The slight depression in the centre of the rampart in the northern extent of the trench represents the remains of a sunken-featured building of early medieval date.
English Heritage. NMR. the exception of the interior of Fort D. Alignment of this map with the photogrammetric plan in AutoCAD Map enabled the identification of breaks in the defences which were probably caused by the network of forestry tracks visible on the map. It is fortunate that in 1925 Simpson and Richmond commissioned a series of air photographs to be taken of their excavations (Fig. 8(a)). The accuracy of the rectifications of these photographs has enabled, in many cases, an exact correlation of trenches and spoil heaps with extant features; these features are colour-coded blue on the interpretative plan. No contemporary detailed plan of the 1920s excavations was published; however, in his 1932 report, Richmond included a location plan for selected features excavated in Fort A and Annexe B (Richmond, 1932, plate XX). This was aligned with the photogrammetric plan which has allowed further identification of specific trenches, including all of Richmond’s so-called ‘‘officers’ dugouts’’ which he interpreted as structures for housing Roman officers (1932, p. 67). One of the ‘‘dugouts’’ was re-excavated in 1999 as part of the current programme of research (trench 2, Figs. 2(b) and 7); significantly, it proved to be a sunken-featured building of
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. 103 Stone and Clowes. Photogrammetric recording of the Roman earthworks ‘‘Cawthorn Camps’’ Table I. List of oblique photographs rectified with photogrammetric plot. Repository Photograph Date Greatest control point error NMR* NMR NMR NMR NMR CUCAP** CUCAP CUCAP SE 7890/8/1 SE 7890/8/1 SE 7890/11 SE 7890/5 SE 7890/4 K26 K26 RC8-E/17 1925 1925 1925 1925 1925 1945 1945 1968 1Æ2 m 0Æ9 m 0Æ9 m 0Æ9 m 0Æ8 m 1Æ8 m 2Æ4 m 2Æ6 m Anthony Crawshaw Anthony Crawshaw Anthony Crawshaw 332/15 332/14 332/14 1993 1993 1993 0Æ7 m 0Æ9 m 1Æ0 m Comments 1920s excavations 1920s excavations 1920s excavations 1920s excavations 1920s excavations World War II features World War II features 1959 firebreak built across the site and afforestation Excellent for internal earthworks Excellent for internal earthworks Excellent for internal earthworks *The ‘National Monuments Record’, the public archive of English Heritage, Kemble Drive, Swindon, SN2 2GZ. http://www.english-heritage.org.uk **Formerly the Cambridge University Collection of Air Photographs, now the Unit for Landscape Modelling at Cambridge University. http://www.aerial.cam.ac.uk Table II. List of vertical photographs rectified with photogrammetric plot. Repository NMR NMR NMR NMR Photograph Date Greatest control point error 01001/7 01001/6 01001/8 01001/2 2001 2001 2001 2001 1Æ0 m 0Æ6 m 1Æ0 m 0Æ5 m Comments Good Good Good Good for for for for internal internal internal internal earthworks earthworks earthworks earthworks Table III. List of plans aligned with photogrammetric plot in AutoCAD Map Release 3. Author Scale Date Comments Ordnance Survey Sir I. A. Richmond (1932, plate XX) 1:2500 Approx 1:1800 1912 1932 Sir I. A. Richmond (1932, 59, fig.12) Approx 1:1150 1932 Royal Commission on the Historical Monuments of England (Welfare and Swan, 1995, 138-139) Ed Dennison Archaeological Services (1998) 1:1250 1992 Tree plantations and tracks Excavation trenches in Fort A and Annexe B Internal earthworks in the south-east quadrant of Annexe B Topographical survey of the entire site 1:200 1998 Digital topographical survey of the southern half of Annexe B early medieval date (Wilson and Lee, 2000b, pp. 20–23). The air photograph interpretation has endeavoured to locate other features across the site which may represent further post-Roman activity, with some potentially interesting results. The area of Cawthorn Camps was used as a training area in the Second World War and rectification of photographs taken in 1945 (Fig. 8(b)) has led to the identification of war-related features some of which are still visible as earthworks today. These include possible bases of Nissen huts and also mortar craters. 104
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. The Photogrammetric Record Two sets of photographs taken in 1993 and 2001 (Fig. 8(c)) show the subtle internal earthworks at Cawthorn very clearly and were key in the interpretation process. Both sets of photographs were taken in low, oblique sunlight effectively highlighting the earthworks; additionally, the 1993 photographs were taken when the site had been extensively grazed by sheep, further revealing the slight features. Some features in Fort A and Annexe B have been identified from these photographs alone; Fig. 8. A series of rectified photographs of Cawthorn Camps (dimensions 720 m · 290 m, area 15Æ5 ha) including: (a) Photographs taken in 1925 showing excavations undertaken in the 1920s (photo references: NMR SE 7890/4–5, 8 [1], 11. 1925.
Simmons Aerofilms Limited. http://www.simmonsaerofilms.com). Fig. 8. (b) Photographs taken in 1945 showing mortar craters (highlighted by red circles) and possible Nissen hut bases (highlighted by red rectangles) in the area of the earthworks (photo references: CUCAP K26-7. 2nd August 1945.
Crown copyright 1945/MOD).
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. 105 Stone and Clowes. Photogrammetric recording of the Roman earthworks ‘‘Cawthorn Camps’’ Fig. 8. (c) Photographs taken in 2001 showing the internal earthwork detail (photo references: NMR 01001/2, 6–8. 26th January 2001.
English Heritage. NMR). these are depicted in yellow on the interpretative plan (Fig. 2(b)). This clearly demonstrates the continuing importance of air photography taken in the right conditions for enhancing understanding of earthwork sites. Conclusion Photogrammetry is frequently used as a tool to study and record buildings and structures. It is less commonly used in archaeological contexts, although recent work at Tell-Mishrife in Syria (Visintini, 2001) demonstrates how aerial photogrammetry can produce valuable ‘‘maps’’ of sites in the form of orthophotographs. Additionally, a project to record an ancient road in Petra, Jordan (Haggren et al., 2001) shows the value of viewing the road in its topographical context by production of a digital terrain model of the area using aerial photography. However, as far as the authors are aware, photogrammetric techniques have rarely been used to facilitate the detailed study and recording of earthwork remains to the level and scale achieved at Cawthorn. The work done here demonstrates the potential for this technique to be used to record earthwork sites, particularly where the application of more conventional ground survey methods are problematic, perhaps because of the extent of the remains, or because of difficult or dangerous conditions on the ground. One other recent project undertaken by English Heritage, investigating remains of the 19th-century alum industry on the coast of north-east England (Topping, 2000; Jecock et al., 2003), has used a similar approach to that at Cawthorn. The use of photogrammetry was particularly pertinent in this case as ground survey was hampered by the treacherous state of the unstable shale cliffs. Photogrammetric plotting produced a detailed and metrically accurate plan of the remains which was then checked and amended, where necessary, by targeted field survey. Another valuable use of this technique is for the recording of archaeological landscapes that are under threat of immediate destruction or damage, where timescale or resources do not allow for other detailed survey to be undertaken. 106
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. The Photogrammetric Record To summarise, the air photographic work at Cawthorn has investigated digital photogrammetry and demonstrated some of its potential uses in an archaeological context. It has illustrated the level of detail which can be obtained from air photographs of sufficiently large scale and quality. It has produced a metrically accurate and detailed interpretative plan of the earthworks at Cawthorn, including the identification of new features not observed through previous field survey. It has shown the value of using historical air photographs and other sources to achieve greater understanding for a site, and it has presented theories for the archaeological remains and highlighted features of interest for future research. Additionally, the large-scale vertical photographs, used in conjunction with photogrammetry, provide an accurate statement of condition for the site as of May 2000 when the photography was taken. This can be used as a baseline for future condition monitoring. This is particularly significant in the case of Cawthorn where visitor erosion is having considerable impact on the earthworks, in particular the ramparts which afford views over the surrounding area. Another potential problem at Cawthorn is the damage caused to the earthworks by sheep, as regular grazing is the only practical way of controlling the vegetation and preventing the regeneration of woodland across the site. Finally, the research work at Cawthorn has demonstrated the benefits of using complementary survey techniques, each of which can contribute its own set of data. Combining the various strands of data allows a more comprehensive understanding of the site to be achieved. Together with the other areas of research, the air photographic evaluation and mapping will inform the future management and presentation of this nationally important site, including the production of the new management plan. The final project report, combining the results of all the areas of research, will be published shortly. references Bewley, R. H., 2003. Aerial survey for archaeology. Photogrammetric Record, 18(104): 273–292. Bryan, P. G. and Blake, W. H., 2000. Metric Survey Specification for English Heritage. English Heritage. 111 pages. Dennison, E., 1998. Annexe B, Cawthorn Camps, Pickering, North Yorkshire. Earthwork Survey. Report commissioned by the North York Moors National Park Authority. 16 pages. Haggren, H., Nuikka, M., Junnilainen, H. and Jarvinen, J., 2001. Photogrammetric approach for archaeological documentation of an ancient road. International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, 34(5/C7): 108–113. Haigh, J. G. B., 1996. Another member of the AERIAL software family. Aerial Archaeology Research Group News, 12: 26–33. Jecock, M., Dunn, C., Carter, A. and Clowes, M., 2003. The Alum Works and Other Industries at Kettleness, North Yorkshire: An Archaeological and Historical Survey. English Heritage Archaeological Report Series AI/24/2003. 100 pages. Johnson, N. and Rose, P., 1994. Bodmin Moor: An Archaeological Survey. Volume 1: The Human Landscape to c1800. English Heritage Archaeological Report 24. Royal Commission on the Historical Monuments of England Supplementary Series 11. 131 pages. Richmond, I. A., 1932. The four Roman Camps at Cawthorn, in the North Riding of Yorkshire. Archaeological Journal, 89: 17–78. Simpson, F. G., 1926. The Roman Camps at Cawthorn, near Pickering. Preliminary Report, 1923. Yorkshire Archaeological Journal, 28: 25–33. Stone, J. L., 2002. Cawthorn Camps, North Yorkshire; Air Photograph Evaluation (Phase II). English Heritage Aerial Survey Report Series AER/8/2002. 121 pages.
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. 107 Stone and Clowes. Photogrammetric recording of the Roman earthworks ‘‘Cawthorn Camps’’ Stone, J. L., 2003. Cawthorn Camps, North Yorkshire—a photogrammetric approach. Archaeological Prospection, 10: 153–157. Topping, P., 2000. Step 4 Industrial Recording: The Alum Industry Module Project Design. English Heritage. 4 pages. Visintini, D., 2001. The aerial photogrammetric surveying of Tell-Mishrife/Qatna archaeological area (central Syria) by digital non-metric images. International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, 34(5/C7): 389–396. Welfare, H. and Swan, V., 1995. Roman Camps in England. The Field Archaeology. HMSO, London. 196 pages: 137–142. Wilson, P., Cromwell, T., Evans, J., Hall, A., Hembrey, N., Usai, R. and Makey, P., 2003. Excavations at Cawthorn Camps, North Yorkshire 1999–2000: Summary Report at Site Archive Completion (with an appendix on survey transects taken for the purpose of earthwork monitoring). English Heritage Centre for Archaeology Report Series 17/2003. 32 pages. Wilson, P. and Lee, G., 2000a. Cawthorn Camps, North Yorkshire. Assessment and Revised Project Design. English Heritage. 166 pages: 29–32. Wilson, P. and Lee, G., 2000b. Cawthorn Camps. Trial excavations 1999: interim report. Yorkshire Archaeological Society Roman Antiquities Section Bulletin, 17: 17–24. Résumé Les camps de Cawthorn constituent un site romain datant probablement de la fin du 1er siècle et du début du 2ème et formé de deux fortifications, dont l’une a une annexe plus récente, et d’un camp proprement dit. Ce site subsiste par des terrassements et des structures défensives dont les principales présentent de nombreux petits remblais. Actuellement le programme de recherche pluri-disciplinaire comporte une prospection géophysique, des fouilles et des relevés terrestres et aériens; il s’agit d’une initiative conjointe de l’Administration du Parc National des Landes du York septentrional et du Patrimoine anglais. Ce projet a pour but d’accroı̂tre les connaissances universitaires sur ce site, d’améliorer les informations diffusées au public et de contribuer à la confection d’un plan destiné à la gestion de ce site d’importance nationale. On a utilisé des photographies aériennes à grande échelle et des traitements par photogrammétrie numérique pour établir un plan à l’échelle de 1:500 et d’une précision de ± 10 cm sur ces terrassements. A partir de ce plan considéré comme carte de base, on a pu redresser d’autres photographies-clés et d’autres plans fournissant des interprétations ultérieures détaillées et indiquant les levés a entreprendre. On a pu également évaluer quelques produits dérivés des photographies aériennes par photogrammétrie numérique, tels que les modèles numériques des altitudes, des orthophotographies et des représentations perspectives. Zusammenfassung Cawthorn Camps ist eine römische Stätte, die vermutlich aus dem späten ersten und frühen zweiten Jahrhundert datiert und die aus zwei Kastellen besteht: eines mit einer späteren Erweiterung und ein zweites mit einem Feldlager. Die Stätte besteht noch immer aus Erdwerken und innerhalb der Hauptverteidigungsanlagen gibt es viele leicht hervorgehobene Strukturen. Das aktuelle fachübergreifende Forschungsprogramm besteht aus geophysikalischen Untersuchungen, aus Ausgrabungen, terrestrischen Vermes108
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. The Photogrammetric Record sungen und Luftbildvermessung und ist eine gemeinsame Initiative der North York Moors National Park Behörde und dem staatlichen Denkmalsschutz. Das Projekt soll das wissenschaftliche Verständnis erhöhen, die Informationen für die Öffentlichkeit verbessern und die Erstellung eines überarbeiteten Planes zur Verwaltung dieses wichtigen Nationaldenkmals unterstützen. Auf der Grundlage von großmaßstäbigen Luftbildern und digitaler photogrammetrischer Auswertung konnte ein Plan im Maßstab 1:500 der Erdbefestigungen mit einer Genauigkeit von ±10 cm hergestellt werden. Dieser Plan diente als Grundlagenkarte für die Entzerrung andere wichtige Aufnahmen und Pläne und erlaubt weitere detaillierte Interpretationen und Kartierungen. Bei der Luftbildauswertung wurden auch einige Produkte der digitalen Photogrammetrie, wie digitale Höhenmodelle, Orthophotos und perspektive Ansichten näher untersucht. Resumen Cawthorn Camps es un asentamiento romano probablemente perteneciente al perı́odo comprendido entre finales del siglo I y principios del II d.c. que incluye dos fortalezas, uno con un anejo posterior, y un campamento. El yacimiento ha perdurado como un conjunto de taludes y, dentro de las defensas principales, hay muchas estructuras ligeramente aterrazadas. El actual programa multidisciplinario de investigación ha incluido la prospección geofı́sica, excavación, y levantamiento aéreo y terrestre, en una iniciativa conjunta de la dirección del Parque Nacional North York Moors e English Heritage. El proyecto pretende incrementar el conocimiento académico, mejorar la información disponible para el público y ayudar en la elaboración de un plan de gestión revisado para este importante yacimiento a escala nacional. Se ha usado fotografı́a aérea a gran escala y fotogrametrı́a digital para generar un plano de los taludes, a escala 1:500, con una precisión de ±10 cm. Este plano ha sido usado como mapa base para rectificar otras fotografı́as y otros planos clave en la posterior interpretación y cartografiado más detallado. También se ha investigado algunos de los productos obtenidos mediante técnicas de fotogrametrı́a digital, tales como los modelos digitales del terreno, las ortofotos y las vistas en perspectiva. Discussion Eric Lange (Veraxis Mundi): Could you say a little bit more about how this metric data really is being used as a tool for managing the site? Jane Stone (English Heritage Aerial Survey Team): As far I understand it, in terms of archaeology, it is not being used in a standard way. But through the work at Cawthorn where erosion is a particular issue, not only visitor erosion but actually erosion by sheep on the site which is the only way of practically keeping the vegetation down, we thought it would be a good way of providing a baseline statement of condition because the photography is so large scale and we have an accuracy of centimetres. Patches of erosion, depth of erosion can be taken off these photographs.
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd. 109 Stone and Clowes. Photogrammetric recording of the Roman earthworks ‘‘Cawthorn Camps’’ Eric Lange: What would you recommend as the time interval of re-shooting the site to determine whether it is being eroded or not? Jane Stone: There isn’t a set idea at all—it is totally ‘‘up in the air’’. It really depends on the site itself. For example, Hadrian’s Wall would be another potential customer for this approach where erosion really does cause a lot of damage. So maybe to start with a rolling programme of every 3 or 5 years, just to get that base level of data then taking it from there. It is not yet happening but we hope it is all to come. [Editor’s note: This discussion continued on this same subject of erosion, but in the context of stone buildings. Since it is possible that a future isssue of The Photogrammetric Record will include the paper to which the continuing discussion more specifically refers, it is truncated at this point.] 110
2004 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd.