Hi Alan,

You'll have to summarise ;)

All the best,
Rui

> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]] On
> Behalf Of Alan Penn
> Sent: 20 December 2005 10:14
> To: [log in to unmask]
> Subject: Re: [SPACESYNTAX] RA or RRA
> 
> Lucas is correct. The issue is associated with the difference between a
> point and a line based representation. Look for example at the difference
> between Axman and Depthmap (in VGA mode). In Axman I stand on an axial
line
> - say Oxford St at Oxford circus - and wherever I walk on that axial line
I
> am on a single node in the graph. I walk east and turn the corner onto
> Tottenham Ct Rd. I am now on another axial line and I am one step away in
> the graph. I walk along the length of TCR and I am always one step away
> until I turn onto Torrington Place. Now I am two steps away. I walk along
> until I reach Huntley Place. Note that I have now been on three lines (and
> so 3 nodes in the graph) but have only been through two changes of
direction
> (links in the graph or points of intersection between lines). Radius in
> Axman refers to the number of nodes involved (ie Torrington Place is
within
> radius 3 of TCR) rather than the number of links.
> 
> Now imagine that I am doing this on a visibility graph. I start at Oxford
> Circus on a point which IS a node in the graph. I can see all the way to
St
> Giles (corner of TCR). This is another point in the Visibility Graph - ie
> another node. The relation of visibility between the two is the link. Thus
I
> have walked along a link in the graph when I reach St Giles. When there I
> can see all the way to the corner of Torrington Place - to another point
> (node). And so on. Now if we standardise on nodes being the radius, three
> nodes (counting the origin) gets me to the corner of Torrington Place but
> not along the street to Huntley Place. What is radius three in Axman is
(by
> convention) radius 2 in Depthmap. This is just a consequence of the move
> from a line to a point based representation. The tricky thing here is that
> since Alasdair is using the same code to calculate both visibility graphs
> and axial graphs in Depthmap, axial radius in depthmap is different to in
> axman.
> 
> I expect that has made it as clear mud! :-)
> 
> Happy Christmas and a merry new year to everyone...
> 
> Alan
> 
> > -----Original Message-----
> > From: [log in to unmask] [mailto:[log in to unmask]] On
> > Behalf Of Lucas Figueiredo
> > Sent: 19 December 2005 13:38
> > To: [log in to unmask]
> > Subject: Re: RA or RRA
> >
> > Hello Sheep.
> >
> > No one is counting from 0. A single topological step means depth 1.
> > There is no topological step from a given line to itself.
> >
> > I know that arrays are confusing in some old programming languages (I
> > also programmed in ANSI C and Pascal) and sometimes we are obliged to
> > change outputs because such limitations of data structure.
> >
> > However, I read lots of papers using R3 and I always understood this
> > radius as 3 steps away, not 2. I also think that in my MSc
> > dissertation wrote that R3 (3 steps) is the local standard radius
> > (which is wrong).
> >
> > These things (interpretations, implementations) must be clear.
> >
> > That is why I reinforce that academic software must be properly
> > published AND cited - because it is part of the methodology you use in
> > experiments. I think we must put it in our software licence "cite it,
> > otherwise do not use it".
> >
> > Regards!
> > Lucas
> >
> >
> >
> > On 19/12/05, Nick Dalton <[log in to unmask]> wrote:
> > > Hi the code in axman was designed to be output compatible with the
> > > fortran code. as a 'C' programmer I found it an odd switch ( and
> > > still do).
> > >
> > > People typically count from one (1,2,3,4) it's only C programmers (
> > > and their children) that count from 0. Fortran and Pascal (object
> > > pascal being the language of Axman) use 1 based indexs for arrays and
> > > so number systems.  Everything also had to be compatible with the
> > > output of the social logic of space ( with the D value).
> > >
> > > Zero depth makes sense to me but non programmers got there first.
> > >
> > > so R2 = r3, r3=r4 and r2=r1, which can be said to eliminate a problem
(
> > no r1).
> > >
> > > Using R2 (ie old R3 )You may noticed more glitches in radius 2 due to
> > > poor micro-structure.
> > >
> > > sheep
> > >
> > > >Dear Lucas,
> > > >
> > > >Yes, this is the same in Depthmap: R2 is the equivalent of R3 in
axman.
> > > >
> > > >I have always said that this makes sense: two steps away is to my
> > > >mind R2, not R3.
> > > >
> > > >As for handling low numbers of lines within (Depthmap's) radius two,
> > > >undefined values (nulls) are given in the (small number of) cases
> > > >where there are too few lines to calculate RRA.
> > > >
> > > >Alasdair
> > > >
> > >