Thank you to Dr Jake Desyllas for such undeserved praise.
Before a brief reply to Jake, I would like to announce a beta release of
our PC Visibility Graph Analysis software, Depthmap.
You can download a demonstration copy of the software for free from:
http://www.vr.ucl.ac.uk/vga/depthmap/
Depthmap is for PC only --- I am afraid there will be no Mac version,
although Sheep (mailto:[log in to unmask]) has written a small program
for the Mac to do the same sort of analysis. As Jake writes,
Intelligent Space are also developing their own version in Java.
As yet, we have not finalised licensing agreements, so for now, please
be content with playing with the demo version, which is almost fully
functional. Our demo licences currently run to June 2000.
To return to the debate. Although we have to some extent solved the
segmentation problem by using visibility graph analysis, we have
unfortunately introduced other problems through our change of
representation. One of the chief advantages of space syntax is that it
is a topological analysis, that it is, the analysis is independent of
the scale of the environment. By introducing a direct representation,
the area of the isovist dominates the integration value of a location.
Although the integration is a good indicator of people movement, where
isovist areas differ dramatically, the indicator breaks down.
As Jake rightly points out, the neighbourhood size, or area, of the
isovist is also a good indicator of observed movement --- this is the
opposite side of the coin: where isovist sizes are not unreasonably
weighted by large open spaces, the first order relationships (i.e., the
area) are a close approximation of the integration value.
What we really need to do is cut the area dependence from the equation:
i.e., go back to a topological analysis of the space. At the moment we
are working on this at UCL by using measures other than integration
which are not directly proportional to the first-order relationships.
Best regards, and thanks to Jake for opening the debate --- keep up the
good work,
Alasdair
--
Alasdair Turner Vitual Reality Centre for the Built Environment
Research Fellow tel +44 20 7679 1806 fax +44 20 7813 2843
University College London Gower Street London WC1E 6BT UK
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