[Freeciv-Dev] Re: (PR#7287) Extended Topologies

["rwetmore@xxxxxxxxxxxx" <rwetmore@xxxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=7287 >


Marcelo Burda wrote:
> Le dim 22/02/2004 à 15:48, Ross Wetmore a écrit :
> 
>>Jason Short wrote:
>>
>>><URL: http://rt.freeciv.org/Ticket/Display.html?id=7287 >
>>>
>>>rwetmore@xxxxxxxxxxxx wrote:
[...]
> Community need to try undestand it to become clear! ;-)

Perhaps you could help by documenting your patch and posting some of the
logical elements as a design document for review. I don't think doc/HACKING
goes nearly far enough as the confusion over something like ratio/size
seems to point out.

[...]
> Pleas! Pleas! Torus is not sphere and Twisted-Torus(that i was called
> Mobius) is not sphere, there are clossed topologies without any type of
> singularities. This are really simplest to code and simlest to play. but
> not at all sphere like.
> Jason continue to speak about torus and twisted-torus as sphere like.
> but there are not sphere like but donut like!!!!

Agreed, a 3-D torus is donut-like.

But the 2-D surface wraps simply in all directions allowing one to travel
in any direction and end back at ones initial point. This is the key property
of the surface of a sphere in 2-D. The 3-D donut vs sphere shape is irrelevant
in the 2-D projection. A 2-D torus-world is not a torus anymore than it is
not a sphere

The key element in mapping a spherical surface onto a 2-D torus-world is
what sort of distortions one gets by different mappings. In general because
there are no folds or inversions from special cuts, but merely variations
of stretches, the adjacency relationships are preserved and only distances
are warped.

Quincuntial produces significant adjacency problems which you have recognized
below. These in effect make it decidely unsuitable for game play, and the
simple torus-world model much more intuitive and hence preferable. These may
not be terminal problems, but I think you are going to have to work out the
solutions, as the rest of us are not as familiar with quincunxes. We can
tell you when your solutions are getting too complex for normal humans to
grasp, though :-).

[...]
> The good point in torus and twisted-torus are this are very easy to code
> and very easy to play in!.

The KISS principle says that this is pretty much a sign that these are
better solutions than quincuntial maps.

I suspect it would probably be best to work on a couple of the residual
problems in doing this as a way to develop a spherical projection than try
to build in quincunx topologies first.

But the underlying problems that quincunxes present are real topological
issues that Freeciv needs to confront and understand to build up its model.
Using quincuntial maps as a vehicle for resolving and building these in is
not a bad way to go if it is done properly, rather than as a one-off hack.

[...]
>>In any event, such a mapping of multiple 2-D images onto the torus surface
>>is pretty much what the quincuntial topology is doing, and figuring out the
>>various ways and relationships between them would perhaaps make the problem
>>less intractable - and of course the code more symmetrical.
> 
> Yes torus is easy, but not sphere like!

I disagree in that the 2-D projection has exactly the properties needed to
emulate a spherical surface with none of the bad ones such as singulatrities.
I think quincuntial maps are neat, but they *really* do not tile well and
have some highly disagreeable properties.

> Can you make a map of real Earth in a torus? no.

Yes. Reread the last posting.

> Can you make a map of Earth in quincuntial? Yes.

The tiled relationships are really screwed up because of the specialized
folding used to handle the southern hemisphere. It also violates Freeciv
GUI presentation rules in its current form. You might be able to come up
with some solutions to these, but until you do, it fails in too many ways
to make it viable as a gaming model.

> Yes quicuntial is a litle harder to code. but i am coded it, pleas help
> me to make it easy to undestand.

Will try to do the mapping to torus for you to show the problems from the
singularities more clearly. In return, please try to come up with alternate
representations or projections that solve or minimize the issues.

And try to understand that 11-year olds really do not understand ideas
like ratios and surface folding. You need to relate things to simple
intuitive models like the size or number of tiles in the x and y axes
of the window they see on the screen, even if you convert this to ratios
in the implementation for some reason.

This does not mean you can't use or talk about other things related to
implementation, but the implementation should be largely hidden from the
user and the simple conceptual models presented for viewing, parameter
input and of course the way things move about in game play. No complex
surprises in any of these, please!

Once you have the user scenarios and concepts right, then implementing
them can be done in any number of ways more appropriate to implementation
issues like robustness, efficiency, maintainability, etc.

[...]
> Marcelo.

Cheers,
RossW
=====