Hi Kerstin,

1) Most differences are due the fact you mapped two different systems.
The visibility graph is an open plan, whereas the axial maps is not of
lines of sight, but of lines of unobstructed movement (see how this
can be complicated?). The fact is that your axial lines are being
traced between ´desks´ (I guess) whereas the visibility points are
not.

Neverthless, the maps are similar, some differences may also be due
the ranges of color (try changing them a bit).

2) Now you changed your original question. All depends of how you turn
both methods useful to your argument. For instance, if you are looking
for ´costs´ of movement, axial lines, as lines of unobstructed
movement, may be more suitable for measuring the complexity of routes
in the building. If you are looking for ´interactivity´ between
people, visibility graphs, and so forth.

Good luck,
Lucas

2008/7/22 Kerstin Sailer <[log in to unmask]>:
> Hi Lucas,
>
> thanks for your reply (and also Alasdair, thanks for the papers, I will
> certainly have a look at them).
>
> Actually I do agree that axial lines in general operate similarly to lines
> of sight. However, I have got one example where my visibility graph
> highlights slightly different areas as best integrated than the axial
> topology.
> I have uploaded both images onto the internet (for those of you who are
> interested in this discussion to have a closer look):
> http://www.kerstinsailer.de/upload/example_axial.jpg
> http://www.kerstinsailer.de/upload/example_visibility.jpg
>
> Note the difference especially on the top floor.
>
> And if I argue that axial lines operate somewhat similar to a visibility
> graph, then why bother discussing both models? (as I do not write a PhD that
> purely discusses syntactical specifities).
>
>
> Cheers,
> Kerstin
>
>
>
> Lucas Figueiredo wrote:
>
> Hi Kerstin,
>
> In this specific case - a building -, in which lines are in the plan
> and cover small distances, you can consider the axial map as a
> simplification of the visibility graph, as axial lines can be roughly
> lines of sight. Just imagine that a 'change of direction' in the axial
> map is like a change of direction in the visibility graph. If you put
> both models side by side, you will notice that the most integrated
> lines cross the most 'visible' points in the visibility graph.
>
> So, the axial line is something like tracing a line over visibility
> points and assigning the 'average visibility' of the points to the
> line. It sounds weird but it works for most measures for visibility
> graphs.
>
> Sheep has done some work using overlapping shapes, which would be an
> intermediate between both. I tested another day to cross the axial
> lines over convex spaces, something that has been done before but for
> some reason did not turn to be popular, and the effects are similar.
>
> Note that in urban areas axial lines are NOT always lines of sight
> (hilly areas, very long lines, for instance). The literature is quite
> misleading in this aspect.
>
> Best Regards,
> Lucas Figueiredo
>
> 2008/7/22 Kerstin Sailer <[log in to unmask]>:
>
>
> Dear All,
>
> for my PhD I am comparing eight different office buildings of knowledge
> intensive work (university, research institute, media companies), but I am
> struggling to come up with a real life meaning of axial topology.
>
> I want to use different syntactical models to compare my buildings:
> 1) a visual graph analysis (Depthmap) based on visibility (i.e. excluding
> furniture and glass walls);
> 2) VGA based on accessibility (i.e. including all furniture, glass walls,
> etc.);
> 3) metric distances based on a segment model;
> 4) axial topology based on an axial line model;
>
> While I find it quite logical to attach the first three categories to real
> life (visibility tells me what people in an office can see; accessibility
> tells me how people can reach every corner of the building; and metric
> distances tells me about the cost of moving around in the building), axial
> topology seems more difficult.
>
> Any ideas anyone?
>
> Cheers,
> Kerstin
>
>
> --
> Kerstin Sailer | 8 Park Avenue North | London N8 7RT | UK
> mobile: +44 77 83404773 | ICQ # 194141160
>
> www.kerstinsailer.de
>
>
>
>
>
> --
> Kerstin Sailer | 8 Park Avenue North | London N8 7RT | UK
> mobile: +44 77 83404773 | ICQ # 194141160
>
> www.kerstinsailer.de



-- 
Lucas Figueiredo