[Freeciv-Dev] Re: (PR#6721) A Quincuncial topology

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=6721 >

Jason Short wrote:
> <URL: http://rt.freeciv.org/Ticket/Display.html?id=6721 >
> 
> Summary:
> 
> This topology is a crazy, kinda cool approximation of a sphere.  To get
> it to work we'd have to have something that I will call
> "mirror-wrapping".  For instance an 8x3 map that mirror-wrapped in the Y
> (north-south) direction would look like
> 
>   xwvutsrq
>   ponmlkji
>   hgfedcba
>   ABCDEFGH
>   IJKLMNOP
>   QRSTUVWX
>   xwvutsrq
>   ponmlkji
>   hgfedcba
> 
> where the capital letters are the normal positions (0,0) through (7,3).
>  Thus for each Y wrap there is a mirroring of the X value
> 
>   Y = Y + map.ysize
>   X = map.xsize - 1 - X

Err, this isn't quite right.  The map is mirrored over the pole with a 
180-degreen (pi) rotation.  So the actual math is a bit more 
complicated, something like

   Y = -Y
   X = map.xsize - 1 - X

-jason