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Visibility analysis in the Stonehenge and Avebury World Heritage Site
 

Visibility analysis in the Stonehenge and Avebury World Heritage Site

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The results of some work I did whilst working for English Heritage, to update the visibility analysis in the Stonehenge & Avebury World Heritage Site GIS. The analysis has subsequently been published ...

The results of some work I did whilst working for English Heritage, to update the visibility analysis in the Stonehenge & Avebury World Heritage Site GIS. The analysis has subsequently been published as part of the WHS Management Plan.

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    Visibility analysis in the Stonehenge and Avebury World Heritage Site Visibility analysis in the Stonehenge and Avebury World Heritage Site Presentation Transcript

    • Visibility analysis in the Stonehenge and Avebury World Heritage Site Paul Cripps GIS Specialist, Archaeological Projects, English Heritage [email_address] CAA UK, University of Southampton, January 21 st 2005.
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Introduction
      • The Stonehenge & Avebury World Heritage Site
      • The WHS GIS
      • Overview of visibility analysis
      • History of visibility analysis using the WHS GIS
      • Revised analysis - methodology
      • Revised analysis - results
      • Further work
      • Conclusions
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 The Stonehenge & Avebury World Heritage Site
      • Unesco World Heritage Convention
      • Inscribed in 1986 as two parts (C373)
      • Avebury: 22 sq. km.
      • Stonehenge: 26 sq. km.
      • Each part has a WHS Coordinator and a Management Plan
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 The WHS GIS - background
      • Set up in mid-nineties to facilitate assessment of Highways Agency A303 proposals at Stonehenge
      • Originally covered Stonehenge only
      • Now covers both parts with a wealth of data
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 The WHS GIS – system
      • Originally Unix-based ArcInfo system
      • Until recently used ArcView3.2
      • Migration to ArcGIS9.0
      • Maintained at EH Archaeological Projects, Portsmouth
      • Users based in EH (Bristol & Amesbury) and Kennet District Council
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 The WHS GIS - data
      • Variety of datasets
      • Primarily for management purposes
      • e.g. designations
      • e.g. published road scheme
      • e.g. basemaps
      • e.g. terrain models
      • e.g. archaeology and geophysics
      • But also a research tool, supporting Stonehenge Research Framework (Bournemouth University)
      • e.g. revised dating for Stonehenge sites
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Overview of visibility analysis - basics
      • Inputs : Raster/TIN elevation model & observer/target locations and offsets
      • Output : Raster coded 1 (visible) or 0 (not visible) ie a simple binary viewshed
      • Processor intensive: many calculations with unoptimised viewshed algorithm
      • Vectors: have both magnitude and direction, so a positive line-of-sight A ->B does not necessary imply B -> A (unless we assume reciprocity of vectors)
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Overview of visibility analysis – cumulative and fuzzy techniques
      • Cumulative viewsheds comprise a number of summed viewsheds from >1 input locations
      • Cell value indicates number of input locations visible from cell or number of input locations which can see cell (assuming reciprocity)
      • Fuzzy viewsheds incorporate controlled error into analysis
      • Monte-carlo approach to produce a distribution of viewsheds
      • Cell value indicates probability of seeing input location from cell or probability of cell being visible from input location (assuming reciprocity)
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Overview of visibility analysis – fuzzy viewshed
      • Calculated from Stonehenge
      • OS LandForm DEM, 10m resolution
      • 1000 iterations
      • Uniform error surface
      • ±2m approximates error in OS LandForm
      • Gives a better approximation of visual envelope associated with the henge: Shades of grey vs. black & white
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 History of visibility analysis using the WHS GIS
      • First analysis undertaken 1997 (Batchelor, 1997)
      • Used a 50m quadrat approach
      • 13 sites for Stonehenge
      • 6 sites for Avebury
      • Used to produce visual sensitivity maps for use in management plans
      • Occasional ad-hoc analyses since relating to planning applications
      143350 415050 Woodhenge 141750 410200 Winterbourne Stoke Group 141620 414600 Vespasian's Camp 142220 412220 Stonehenge 144200 409300 Rollestone Camp Tumuli 145900 410200 Robin Hood's Ball 142950 413700 Old Kings Barrow Group 142250 413433 New Kings Barrow Group 140200 410830 Lake Barrow Group 145198 412800 Durrington Barrow Group 142800 411850 Cursus Barrow Ridge 141390 413450 ConeyBury Hill 141300 411655 Bush Barrow Northing Easting Location 167737 410454 West Kennet Long Barrow 168530 410010 Silbury Hill 169310 410340 Waden Hill 168025 411827 The Sanctuary 169980 410240 Avebury Henge 171460 408720 Windmill Hill Northing Easting Location
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Revised analysis - methodology
      • Same elevation model; OS LandForm, 10m resolution but no quadrats
      • Same sites; 13 for Stonehenge, 6 for Avebury
      • 500 iterations per site to produce individual fuzzy viewsheds
      • Scripting accomplished using Avenue for ArcView3.2
      • 4500 viewsheds calculated in total, taking 1-2mins per viewshed, about 75 hours total processing time to produce data
      • Fuzzy viewsheds summed to produce cumulative fuzzy viewsheds
      • Cumulative fuzzy viewsheds used to produce visual sensitivity maps
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Revised analysis - results
      • Fuzzy viewsheds provide better approximation of visual envelopes for study sites
      • Cumulative fuzzy viewsheds provide better approximation of visual sensitivity wrt the input sites
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Revised analysis - Stonehenge results
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Revised analysis - Avebury results
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Further work
      • Can be used in conjunction with other datasets in the WHS GIS e.g. extensive geophysics from A303 evaluations
      • Detailed investigation of viewsheds for each site
      • Aim to improve error model to account for spatial autocorrelation of error: Topographic survey or LiDAR as independent dataset (after Carlisle) to build error surface
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 Conclusions
      • Fuzzy approaches to visibility analysis provide better approximation of real-world situation
      • The visual sensitivity maps are a key resource within the site management plans
      • Are being used in discussions relating to WHS borders and buffer zones
      • Still room for improvement in the model
    • Visibility analysis in the Stonehenge and Avebury World Heritage Site CAA UK 2005, University of Southampton, January 21 st 2005 fin