Isovist AnalystArcView 3 Extension for Urban Viewshed Analyses

Sanjay Rana

BackgroundIsovist Analyst

DescriptionAn isovist is a term used in urban planning for the area visible from a viewpoint (see figure below). Isovist Analyst is an ArcView 3.x extension for computing several properties of isovists e.g. isovist area, shape of isovists (see bottom right figure).

Minimum Requirements• Lines or Polylines or Polygons

as obstacles.• Points as viewpoints.Download & Information• www.ucl.ac.uk/~ucessan/• Free for personal and non-

profit purposes. • Comments/queries are

welcome at s.rana@ucl.ac.uk

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Mesh of viewpoints in Tate Britain Gallery, London

Isovist Area Longest Diameter Length

High Low

Isovist

Isovist Descriptors

Viewpoint

Photograph of the area taken at the viewpoint looking North-West

T. Joliveau

Potential Applications of Isovist AnalystAutomated Generation of Geographical Context in Photograph Databases

Thierry Joliveau~ and Sanjay Rana~Université Jean Monnet- Saint Etienne, FranceProblemThe large databases of digital photographs collected by the public (e.g. flickr, panoramio) and government often lack geographical context such as part of the city where the photographs were taken, geographic objects (e.g. statues, buildings, hills etc.) visible in the photographs and so on. SolutionThe EXIF tags of geo-tagged photographs contain the exact geographic location, azimuth, and field of view, which can be used to construct the viewshed-polygon of these photos. Now, with simple intersection tests between the landmark features and viewshed of photos, one could automatically construct the geographical context (e.g. keywords) for these photos e.g. for the purpose of gazetteer based querying of photograph databases e.g. Show me all the photos that have a view of the Statue in Place Jacobins in Lyon (France).

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Sites where photos of

downtown Lyon (France) are

available in the Photographs

database

The Statue in Place Jacobins

Isovists of photos that contain the Statue 2

1

Photos corresponding to the selected isovists

T. Joliveau

T. Joliveau

Potential Applications of Isovist AnalystEnhancing Wayfinding Instructions with Visibility of Local Landmarks

ProblemMost automated wayfinding instructions for route planning and general sight-seeing are based on the use of transport network features e.g. turn left at street x on to street y and so on. We however also often include other cues such as visibility of local landmarks in our referencing scheme, which is particularly significant when the transport network signs are not available due to poor signage or inside buildings (e.g. museums).SolutionAn intuitive and humane set of wayfinding instructions can be produced by carefully inserting the visibility of certain key landmarks along the proposed route as they become visible at each step of decision making.

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Further Information• Read more in Martin Raubal and Stephan Winter, 2002, Enriching

Wayfinding Instructions with Local Landmarks, GIScience 2002.

Google-TeleAtlas

UCL

Museum

Walking Directions from UCL to British MuseumArea and Landmarks Conventional

instructions

Bookshop Senate House

Turn Left onto Gower Street

Continue onto Bloomsbury

Street

Turn Left into Great Russell

Street

Improved instructions

Turn Left onto Gower Street, [Keep going past Torrington

Place intersection where there is a bookshop]

[You will see the Senate House on your left at the Gower Street-Store Street

intersection]

Continue onto Bloomsbury Street. [You will see…]

Potential Applications of Isovist AnalystPlanning and Evaluating Coverage of Visual Surveillance Network Installations

Further InformationRead about a real example in page 10 of the UK Home Office Research Report on Methods used in assessing the impact of CCTV, Available at www.homeoffice.gov.uk/rds/pdfs05/rdsolr1705.pdf 4

ProblemThe planning and evaluation of a visual surveillance network e.g. CCTV is a complicated and delicate process. The objective of planning and evaluation is to ensure the maximal visual coverage with a minimal number of visual surveillance sites. The coverage influences the effectiveness of the surveillance, which is relevant in the evaluation.SolutionAn add-on to the Isovist Analyst, called Art Gallery Problem Solver can find out a minimal number of viewpoints that provide a complete visual coverage of an arbitrary open space. This can be useful for planning a CCTV network and evaluating the coverage of existing CCTV cameras.

Mesh of Potential Sites for CCTV Camera Installation in

downtown Lyon (France)

65 Sites for CCTV Camera Installation which will provide

complete Visual Coverage

Potential Applications of Isovist AnalystPlanning and Evaluating Coverage of Visual Surveillance Network Installations

Further InformationRead about a real example in page 10 of the UK Home Office Research Report on Methods used in assessing the impact of CCTV, Available at www.homeoffice.gov.uk/rds/pdfs05/rdsolr1705.pdf 4

ProblemThe planning and evaluation of a visual surveillance network e.g. CCTV is a complicated and delicate process. The objective of planning and evaluation is to ensure the maximal visual coverage with a minimal number of visual surveillance sites. The coverage influences the effectiveness of the surveillance, which is relevant in the evaluation.SolutionAn add-on to the Isovist Analyst, called Art Gallery Problem Solver can find out a minimal number of viewpoints that provide a complete visual coverage of an arbitrary open space. This can be useful for planning a CCTV network and evaluating the coverage of existing CCTV cameras.

Mesh of Potential Sites for CCTV Camera Installation in

downtown Lyon (France)

65 Sites for CCTV Camera Installation which will provide

complete Visual Coverage