1. Isovist Analyst
ArcView 3 Extension for
Urban Viewshed Analyses
Sanjay Rana

2. Background
Isovist Analyst
Description Minimum Requirements
An isovist is a term used in urban • Lines or Polylines or Polygons
planning for the area visible from as obstacles.
a viewpoint (see figure below). • Points as viewpoints.
Isovist Analyst is an ArcView 3.x Download & Information
extension for computing several • www.ucl.ac.uk/~ucessan/
properties of isovists e.g. isovist • Free for personal and non-
area, shape of isovists (see profit purposes.
bottom right figure). • Comments/queries are
welcome at s.rana@ucl.ac.uk
Isovist Descriptors
Isovist
Mesh of viewpoints
in Tate Britain
Gallery, London
Viewpoint
© T. Joliveau Isovist Area Longest Diameter
Length
Photograph of the area taken at the
viewpoint looking North-West High Low
1

3. Potential Applications of Isovist Analyst
Automated Generation of Geographical Context
in Photograph Databases
Thierry Joliveau~ and Sanjay Rana
~
Université Jean Monnet- Saint Etienne, France
Problem
The 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.
Solution
The 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).
1
The Statue in
Place Jacobins
2 © T. Joliveau
Sites where
photos of
downtown Lyon
(France) are © T. Joliveau
available in the Photos corresponding to
Photographs the selected isovists
database
Isovists of photos that
contain the Statue 2

4. Potential Applications of Isovist Analyst
Enhancing Wayfinding Instructions with
Visibility of Local Landmarks
Problem
Most 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).
Solution
An 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.
Walking Directions from UCL to British Museum
Area and Landmarks Conventional Improved
instructions instructions
UCL
Turn Left onto Turn Left onto Gower Street,
Gower Street [Keep going past Torrington
Bookshop Senate Place intersection where
Continue onto
House there is a bookshop]
Bloomsbury
Street [You will see the Senate
Museum House on your left at the
Turn Left into
Gower Street-Store Street
Great Russell
intersection]
Street
Continue onto Bloomsbury
©Google-TeleAtlas Street. [You will see…]
Further Information
• Read more in Martin Raubal and Stephan Winter, 2002, Enriching
Wayfinding Instructions with Local Landmarks, GIScience 2002. 3

5. Potential Applications of Isovist Analyst
Planning and Evaluating Coverage of Visual
Surveillance Network Installations
Problem
The 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.
Solution
An 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 65 Sites for CCTV Camera
Camera Installation in Installation which will provide
downtown Lyon (France) complete Visual Coverage
Further Information
Read 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

6. Potential Applications of Isovist Analyst
Planning and Evaluating Coverage of Visual
Surveillance Network Installations
Problem
The 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.
Solution
An 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 65 Sites for CCTV Camera
Camera Installation in Installation which will provide
downtown Lyon (France) complete Visual Coverage
Further Information
Read 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