Re: topology files

[Seth Teller <teller@csail.mit.edu>]

patrick et al.,

comments follow.

Patrick J Nichols II wrote:
> Some replies:
>
> - portals do have a well defined source and dest. HOWEVER, portal's 
> don't have a notion of directionality. Do you think this is a serious 
> problem with the model?

making portals directional (i.e., making the representation a
digraph, rather than a graph) is a good idea for at least two
reasons.  first, it makes it easier to build the space/portal
graph lazily, on demand -- since you can instantiate space A,
and portal from space A to a space "to-be-determined," without
committing to instantiating the opposing portal.

second, portals are not always symmetric, that is, portal
A->B may have different properties than portal B->A.  the
simplest example of this is a door that requires cardkey
access to traverse.  the route-planner needs to consider
that traversing (say) the A->B direction requires an ID.
but since the B->A direction goes from a secure to an
insecure space, traversing the portal in this direction
does not require an ID.

rather than tagging the spaces on either side of the portal,
and trying to make inferences about the portal from the tags,
my view is that we should simply attach to the portal every-
thing we know about it, as a function of the direction in
which it is encountered/traversed.

> - some times portals have an explicit type in the data (stairs vs. 
> elevator shafts vs. windows), and it probably makes sense to save those 
> types rather than inferring them from bell's code. ergo, we save them in 
> their text representation. additionally, i'm not really sure how to go 
> about inferring portal types in certain scenarios -- i.e. its really 
> unclear how to tell an elevator shaft from a staircase, and they are 
> very different times.

i'm sorry, this is still not clear to me.  stairs and shafts are
spaces.  windows are portals (for visibility, or for emergency exit
purposes).  why are you conflating them?  also, when you says it's
hard to tell a shaft from a staircase -- do you mean it's hard for
the walls program to distinguish these space types?  michael, is this
correct?  my impression was that it was not hard.

seth

> -Patrick
>
> At 03:14 AM 9/24/2003 -0400, Seth Teller wrote:
>
> > comments:  the spec should state that contours are
> > oriented, and how.
> >
> > portals should have a well-defined source and dest
> > space.
> >
> > why do portals have types?  shouldn't a portal
> > be able to infer its type from the type of its
> > destination space?
> >
> > seth
> >
> > Michael Craig wrote:
> >
> > > this is for patrick especially,
> > >
> > > here's a quick spec for the (new) topology output from walls:
> > > http://graphics.lcs.mit.edu/~mic/bmg/topology.html
> > > it's not quite formal but it's a pretty dead-simple spec.
> > >
> > > michael