Trevor Pearson & Paul Bryan, English Heritage

1. Recent Survey work at
Stonehenge
Trevor Pearson Paul Bryan

7. • 2009 survey in progress

12. • Watercolour of the mound

14. • Photo of Greenhatch working

21. Recent survey work at
Stonehenge
- the standing and fallen stones
Paul Bryan BSc
Geospatial Imaging Manager
Remote Sensing Team, Investigation & Analysis Division
Heritage Protection Department
English Heritage
37 Tanner Row, York, YO1 6WP

22. Existing survey material
• Within the NMR’s Historic Plans Room a wide variety of
survey material already exists for the Stonehenge site
• Includes aerial photographs, topographic and elevational
surveys:
• 1:500 scale topographic survey produced by Plowman
Craven & Associates (PCA) in 1974
• 1:50 scale topographic survey of the stone circle
produced by MJ Rees & Co in 1989
• 1:10 scale hand measured survey of stones produced by
EH Survey team in 1974
• Very little measured survey exists on the standing and fallen
stones themselves

23. Previous detailed survey
• As stated in Archaeological Survey and Investigation’s (AS&I)
Stonehenge WHS landscape project design:
“In 1993, photogrammetric survey provided what is probably the
most complete survey of the standing stones to date”
• This utilised ‘traditional’ film-based stereo-photography and
theodolite survey control approaches on site
• Post-processing was carried out using one of the ‘new’
Digital Photogrammetric Workstations (DPW)
• Pixel-matching software used to automatically create 3D
surface models for each stone at 2cm resolution

24. Application of modern survey techniques at Stonehenge
• Since 2006 low-cost photogrammetric approaches, as used
within the Northumberland & Durham Rock Art Project
(NADRAP), have been trialled at Stonehenge
• These demonstrated potential to automatically capture
higher resolution 3D surface data, with mm point spacings,
using stereo-imagery captured by both compact and DSLR
cameras
• Until last year, modern laser scanning systems had not been
systematically used at Stonehenge
• …so what advantages would they bring?

25. Laser Scanning
Advantages:
• Laser scanning is applicable on all 2D and 3D surfaces
• Very fast – captures up to 500,000 3D points per second
• Depending on scanner can provide very detailed, sub-millimetric
accuracy 3D data
• Can integrate imaging using on-board CCD or external DSLR
• Excellent for objectively recording three dimensional surfaces
• Ideal for recording, monitoring, modelling and visualisation
Disadvantages:
• Produces very large data files, still often difficult to view in full
resolution without high-end computers and dedicated software
• Hardware expensive – currently between £30K - £110K
• Requires sophisticated software to post-process point data
• Capture of discrete edges needs high-resolution point data
• Usable line-based output still requires manual digitisation
Longthorpe Tower, nr Peterborough
Images courtesy of Oakes Surveys • But heritage application rapidly maturing!

26. Previous application of laser scanning at Stonehenge
• Ad-hoc application includes work undertaken by Wessex
Archaeology and Archaeoptics back in 2002/03
• As noted on the Stonehenge Laser Scans website -
http://www.stonehengelaserscan.org/index.html - this
investigated the application of close-range scanners, e.g.
Minolta VI-900, to record the stone surfaces and provide
potential for revealing new carvings
• Generated a lot of media interest!
• Also carried out trials of terrestrial laser scanning using a
Riegl Z360 supplied by 3D Laser Mapping
• However as the website states “Many more scans need to be
taken to enable us to capture every facet of the monument, and
create a complete model of Stonehenge”

27. Proposed application of laser scanning within AS&I project
• The AS&I’s landscape survey project design noted:
“the detailed survey of the ‘dagger’ carvings and other graffiti
might be improved dramatically and indeed possible unknown
artwork detected by using modern scanning technology. The
research potential this offers justifies preparation of a laser
scan”
• Rather than concentrating on just the standing/fallen stones
and carvings, this would complement and contribute to AS&I’s
recording across the Stonehenge WHS landscape using their
own respective survey approaches
• Funded through EH’s National Heritage Protection
Commissions Programme (NHPCP)
N
Image supplied through Pan Government
Agreement (PGA)

28. Proposed application of laser scanning within AS&I project
• Landscape within the ‘triangle’ – using terrestrial laser
scanners to capture a point-spacing of at least 10cm
• The stone circle and ‘bank & ditch’ – using terrestrial laser
scanners to capture a point-spacing of at least 2cm for the
landscape and up to 1mm for the stone circle
• The standing and fallen stones - using close-range and/or
high-resolution terrestrial scanners & digital imaging to capture
as many visible faces of the stones at a point-spacing of at least
0.5mm
N
Image supplied through Pan Government
Agreement (PGA)

29. Laser scanning undertaken by Greenhatch Group
• Following pre-qualification and tendering the successful
contractor was the Greenhatch Group (based in Little Eaton
near Derby) who proposed:
• Landscape within the ‘triangle’
• Leica C10 long range laser scanner
•The stone circle and ‘bank & ditch’
• Z+F 5006h short range laser scanner equipped
with calibrated M-Cam
• The standing and fallen stones
• new Z+F 5010 high resolution, short range laser
scanner
• Nikon D3x DSLR
• Digital imaging of each stone surface
• Stereo-photography for tops of each
N
Image supplied through Pan Government stone/lintel using ‘Jimmy Jib’ boom
Agreement (PGA)

30. Site work and initial assessment
• Site work commenced on 22nd February 2011 and completed
by 18th March, as per agreed programme
Images by James Davies © English Heritage
• Initial assessment of existing survey materials undertaken by
Caroline Hardie from Archaeo-Environment Ltd,
Greenhatch’s appointed archaeological sub-contractor, who
noted that:
“This report will summarise some of the earlier findings, but the
advantage of laser scanning is that it is objective and so the
methodology used need not be altered to accommodate existing
discoveries. We are as keen to explore the gaps in our
knowledge as well as the areas where research has already
been carried out.”

31. Post processing
• Post-processing carried out between 28th February and 20th
May 2011 including:
• Registration and geo-referencing of ‘raw’ scan data
using Leica Cyclone software
• Generation of ‘Truview's from registered data using
Leica Cyclone Publisher software
• Photogrammetric processing of upper surfaces using
Photomodeler Scanner software
• Meshing and generation of 3D models for each stone
using Geomagic Wrap/Studio software

32. Initial outputs
• Digital Surface Model (DSM) of ‘The Triangle’ landscape @
100mm and Bank and ditch @ 20mm resolution

33. Initial outputs
• Digital Surface Model (DSM) of ‘The Triangle’ landscape @
100mm and Bank and ditch @ 20mm resolution
• 3D model of stone circle @ 1mm resolution

34. Initial outputs
• Digital Surface Model (DSM) of ‘The Triangle’ landscape @
100mm and Bank and ditch @ 20mm resolution
• 3D model of stone circle @ 1mm resolution
• Digital surface data for all standing & fallen stones @ 0.5mm
resolution

35. Initial outputs
• Digital Surface Model (DSM) of ‘The Triangle’ landscape @
100mm and Bank and ditch @ 20mm resolution
• 3D model of stone circle @ 1mm resolution
• Digital surface data for all standing & fallen stones @ 0.5mm
resolution
• Summary assessment of initial archaeological findings,
including landscape and stone surfaces, using Meshlab
• increased knowledge on stone working
• ‘grooves’ from stone dressing divided into sections ->
different teams of builders?

36. Detailed archaeological analysis of stones (6457)
• A detailed archaeological analysis of every visible surface of
every stone is due to commence in March
• Funded through NHPCP this will inform further research,
monitoring & presentation of the monument….
• …and provide an analytical report, with associated stone
‘biography’, graphic record & catalogues, answering the
following research questions:
• Evidence for the methods employed in building
Stonehenge, in particular shaping the stones
• Evidence for prehistoric carvings on the stones
• Evidence for later alterations to stones and graffiti
• Evidence for architecture and sequence at Stonehenge
• To be undertaken by ArcHeritage (Sheffield) and due for
completion in early May

37. Filtering the data (6456)
• Due to the extensive coverage of the stones by different
types of lichen some surface sections are obscured
• Aim of this new NHPCP funded project is to investigate a
method for digitally filtering out this lichen cover and other
anomalies from the existing scan data, in order to maximise
the view of the underlying stone surface
• Experimental work looking at the combination of data
already acquired:
• Raw & registered 3D point data
• Laser intensity
• RGB colour for each scanned point
• Separate DSLR imagery
• Undertaken by CyArk (USA) and due for completion in
early March it will feed into the analysis project (6457)

38. Some issues to consider
• Data density
• Difficulty of viewing high resolution datasets without
resorting to decimation
• Requires high-end computing hardware and specialist
viewing software
• Limits potential access to high resolution dataset
• Archiving
• Over 850GB of data so far generated comprising:
• Raw scan data (ASCII & proprietary) – E57?
• Registered scan data (ASCII & proprietary)
• Mesh model data (OBJ) - 3DPDF?
• ‘Truview’ data (proprietary) – other options?
• Digital image data (RAW & TIFF)

39. “Surveying Stonehenge” – Geomatics World article
Geomatics World Nov/Dec 2011 & Jan/Feb 2012
www.pvpubs.com

40. Thank you for listening
Geomatics World Nov/Dec 2011 & Jan/Feb 2012
www.pvpubs.com