A presentation given in May 2005 at the McDonald Institute for Archaeological Research, University of Cambridge, on behalf of the Stonehenge Laser Scan project team. The presentation was aimed at highlighting some of the results and well as the technologies used.

1. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Of Henges, Rock Art & Lasers…
An application of Laser-Scanning
techniques at Stonehenge, Wilts.
Paul Cripps
GIS Specialist, Archaeological Projects, English Heritage
Postgraduate Research Student, Archaeological Computing Research Group (ACRG), University of Southampton
On behalf of the Project Team

2. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Presentation Outline
 Background
 Project Team
 Aims & Objectives
 Equipment used
 Related projects
 Methodology 1; Data Capture & Processing
 Terrestrial Laser-Scanners and Airborne LiDAR
 Large datasets!
 Registration
 Decimation
 Methodology 2; Analysis of Results
 Three-dimensional digital surface models (DSM)
 Geometric transformation & analysis
 Lighting & Shading
 Animation
 Results
 The Henge
 Stone 53 carvings
 Stone 3 carvings
 Stone 4 carvings
 LiDAR
 Conclusions
 Review of aims & objectives
 Potential for Rock Art research

3. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Background

4. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Introduction
 Project initiated to assess usefulness of commercial
laser-scanning techniques to an archaeological unit
 Brought together an archaeological unit and commercial
laser-scanning companies
 Used a range of techniques on nearby sites for
evaluation purposes

5. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
The Project Team and those involved
 Wessex Archaeology:
 Chris Brayne (IT Manager)
 Thomas Goskar (Multimedia Development Officer)
 Paul Cripps (Systems Development Officer)
 Archaeoptics:
 Alistair Carty (Director)
 Dave Vickers (Technician)
 3D Laser Mapping
 Dr. Graham Hunter (Managing Director)
 English Heritage:
 Paul Cripps (GIS Specialist, Stonehenge & Avebury
World Heritage Site GIS)
With special access to the stones granted by English Heritage

6. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Aims & Objectives
1. To assess usefulness of
terrestrial (& airborne) laser-
scanning techniques as survey
tools
2. To record the known inscribed
rock art at Stonehenge
3. To assess the potential for
future work at Stonehenge

7. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Equipment used
 Riegl Z360 ‘Time-of-Flight’ scanner
 Basically a super-TST
 360° horizontal scanning range
 90° vertical scanning range
 Relatively low resolution
 Minolta VI-900 ‘Triangulating’ scanner
 Behaves more like a camera, recording position of
an emitted stripe of laser light
 Very high 170µ resolution (0.17mm)

8. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Related Work at Stonehenge
 English Heritage Aerial Survey Team
 Looked at the Environment
Agency LiDAR dataset in
collaboration with Cambridge
University (Colin Shell)
 Mini-project to assess use of
LiDAR as a prospection tool for
archaeological features, similar to
aerial photograph transcription
 English Heritage’s Stonehenge 3D
 Collaboration with Intel & IBM
 Used photogrammetric model of
the stones as 3D source data
(English Heritage Metric Survey
Team)
 Terrain model derived from OS
LandForm data

9. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Historical Context

10. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Stonehenge
 Located on Salisbury Plain
 Part of the Stonehenge & Avebury
World Heritage Site
 Multi-phase henge
 Earliest phase Middle Neolithic:
bank and ditch with wooden posts
inserted into bank in the Aubrey
Holes
 Second phase Late Neolithic:
remodelling of ditches, wooden
posts within henge, Aubrey Holes
partially silted up
 Third phase Late Neolithic/ Early
Bronze Age: Bluestone and
Sarsen megaliths added

11. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Stonehenge
 Part of a complex
archaeological
landscape
 Surrounded by approx.
700 individual
monuments; barrows,
cursuses, enclosures,
henges, field systems,
etc
 Archaeology from all
periods from prehistory
to modern airfield

12. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
The Prehistoric Carvings
 First observed in 1953 (Atkinson,
1953; Crawford, 1954; Atkinson,
1979 pp43-4)
 Found on the Sarsen stones
 Sarsens thought to have been
brought from Marlborough Downs,
nr. Avebury
 Likely to have been carved after
erection of the stones based on
distribution
 Thought to represent Bronze Age
axes and daggers
 Axe almost identical to carvings
found in nearby Bush Barrow,
deposited wrapped in cloth
 Other sarsens near Avebury show
axe grinding marks

13. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Previous work on the carvings
 Robert Newall took casts and
rubbings of carvings on stones 3 & 4
 43 casts (mainly by Newall) stored in
Salisbury Museum
 1967 Atkinson took latex mould of
part of Stone 53, subsequently
stereo-photographed and used to
produce a 0.5mm contour plot
(Atkinson, 1968)
 Photogrammetric survey (Bryan &
Clowes, 1997) led to renewed
interest in carvings, with a project
outline (1999) by Burton, Pitts &
Wheatley (never initiated)

14. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Methodology; Data Capture & Processing

15. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Scanning Technologies
 Two systems used on site:
 Time-of-flight scanner
 Triangulating scanner
 Data from a third system incorporated
 Airborne LiDAR, produced by the Environment Agency,
provided by English Heritage

16. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Time-of-Flight scanners
 Fire a laser beam, measure
time taken for beam to return
 Records bearing from scanner
 Uses speed of light constant c
to calculate range
 Also records other properties
of reflected laser beam (eg
intensity)
http://www.i3mainz.fh-mainz.de/publicat/cipa2001/cipa2001.pdf

17. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Triangulating Scanners
 Fire a laser beam from a
known point
 Observe laser beam from a
known displacement
 Use triangulation principles to
calculate x,y,z location on
target relative to scanner
 Much higher resolutions
 Digital camera can also be
used to capture photographic
information
http://www.i3mainz.fh-mainz.de/publicat/cipa2001/cipa2001.pdf

18. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Airborne scanners
 Time-of-flight systems
attached to an aircraft
 Incorporates dGPS for
location and uses onboard
sensors to detect
orientation and aspect
 Calculate x,y,z location on
target
 Transform data to any
coordinate system (eg
British National Grid)

19. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Laser-scan datasets - points
 Raw data made up of
thousands of recorded points
(a ‘point cloud’)
 Each point has x,y,z locations
(plus other attributes)
 Very large filesizes (100,000
points captured per second on
some systems!)
 Difficult to visualise complex
datasets
http://www.archaeoptics.co.uk/downloads/presentations/m3/6.html

20. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Laser-scan datasets - processing
 Point clouds require processing
 Can be seen as a statistical distribution
representing probability of a surface
occupying a particular space
 Possible to fit a surface to the point
cloud using best-fit algorithms…
 …or force a geometric primitive to fit
(makes assumptions)
 Surfaces much easier to manipulate;
hardware acceleration on graphics
cards aimed at gaming is ideally suited
to manipulating surface data
 Better representation of the real-world
situation

21. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Registration
 Multiple datasets must
be ‘stitched’ together
 Can be accomplished
using control points http://www.pobonline.com/CDA/ArticleIn
placed in each scan… formation/Article/1,9169,83255,00.html
 …or by matching the
surfaces within
controlled parameters…
 … or a combination
http://www.research.ibm.com/vgc/pdf/te
xalign_TVCG.pdf

22. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Decimation
 Sheer volume of data can be unusable
 Many millions of polygons
 Process called decimation reduces level-of-detail
according to usage requirements
 Different levels of detail required for different
purposes eg rock art analysis, web dissemination,
desktop visualisation, etc

23. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Decimation – surfaced model

24. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Decimation - wireframe

25. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
The Real World
 Data can be placed in real-world coordinates (eg
British National Grid)
 Allows multiple datasets to be placed in a
common coordinate system (eg airborne LiDAR,
close range scans, time-of-flight scans, other
DTMs, photogrammetric surveys, geophysical
survey data, etc)
 Facilitates integration with GIS

26. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Methodology; Analysis

27. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
From Points to Digital Surface Model
 Triangle mesh produced
from point cloud
 This digital surface model
can be manipulated in a
virtual 3D world
 Ideally suited to rock art
analysis:
 Oblique lighting techniques
 Dynamic lighting techniques
 Geometric analysis
http://www.polygon-technology.com

28. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Lighting techniques; oblique lightning
 Low angle light
source emphasises
carvings
 Easy to control,
unlike in the real-
world; not dependent
on external factors

29. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Lighting techniques; dynamic lighting
 A moving light
source can highlight
otherwise
imperceptible
surface features
 Our eyes highly
attuned to detecting
subtle changes in
light and shadow

30. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Lighting techniques; dynamic lighting

31. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Geometric techniques; exaggeration
 A digital surface model
can be manipulated in 3D
space
 Vector based
transformations X1
 Including stretch along z-
axis or vertical
exaggeration
X 10

32. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Geometric techniques; accessibility
shading
 Possible to code surface
according to accessibility
 Use balls of varying sizes
to probe surface
 More accessible locations
receive greater score

33. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Geometric techniques; range colouring
 Possible to code surface
according to range from
viewpoint…
 … or specified plane or
point
 Range in this image from
black to white: 5mm

34. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Results

35. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
The Henge; time-of-flight scan
 Single 360° scan
undertaken from
central location
within Henge
 Provides spatial
framework for
detailed scans

36. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
The Henge; increasing resolution
Animation
 Gives the impression of a ‘complete’ henge when viewed from
scanner location
 Animation shows transition between datasets in the same
coordinate system

37. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Stone 3 carvings
 The lower left part of the
outer face of Stone 3
contains the carvings of
three axe heads.
 These can be seen with
the naked eye when
close to the stone, and
were easily picked up by
the scanner.

38. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Stone 4 carvings
 The greatest number of carvings on any one stone at
Stonehenge is on the outer face of Stone 4
 The annotations indicate the locations of carvings

39. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Stone 53 carvings
 The famous dagger
and axe are clearly
visible in the centre of
the scan
 As is the historical
graffiti
 And two seams in the
sandstone

40. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Stone 53 carvings
 A comparison
with Newall’s
recording
shows two
previously
undiscovered
carvings
 Very shallow
and indistinct
compared to
known
carvings

41. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Stone 53 carvings

42. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
LiDAR
 Possible to
identify and
quantify extant
archaeology
 Some new
features
identified
 Require
validation

43. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
LiDAR - animation

44. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Conclusions

45. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Laser-scanning
 A very useful survey tool, complements
tools already in use
 Rapid data acquisition
 Ideal for recording surfaces
 High resolution, suitable for recording
ephemeral carvings
 True 3D data ideal for analysis
 Erosion monitoring & volumetric analysis

46. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
The prehistoric carvings
 Current records are incomplete; many
more carvings than are currently known
 The carvings have been considerably
eroded since first carved, arguably since
recorded in 1950’s
 Accurate recordings of morphology of axe
& dagger carvings

47. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
Future work
 Evaluation successfully highlighted
potential of technique
 Systematic survey of all stone surfaces at
sub-millimetre accuracy (new scanners
capable of 80µ resolution)
 Aim: to provide a 3D baseline dataset for
management and research purposes

48. McDonald Institute for Archaeological Research, University of Cambridge, May 2005
fin
For more information:
www.stonehengelaserscan.org
With thanks to Tom Goskar and Alistair Carty for their assistance with this presentation