Subject: Re: Registration of text/calendar MIME property GEO_BOUNDS

From: [email-masked]
Date: Tue, 22 Aug 2000 16:03:45 -0400

>>  Given the political fragmentation of our fine planet, there are likely
>>  time zones with holes in the middle, or broken into several distinct
>> pieces.  (GIS folks refer to these as lakes and islands.)  It doesn't
>> look to me like the current  proposal has any way of addressing this
>> issue.

>I had not thought of the hole in the middle problem.
>
>Would something like "GEO_BOUNDRY_EXCEPTION: <sets-of-points>" do?
>It would describe holes.

I seem to remember that the CGI, GKS, PHIGS computer graphics standards 
had a POLYGON_SET primitive. So maybe you don't really need the exception 
property? 
If you include a set of polygons there is a well know algorithm to find 
out if a coordinate is in the inside or outside of the set.
But then, this would only require the CUA to convey to the CS a single 
LAT/LON coordinate (and a date/time value?) for the CS to calculate which set of time zones correspond to the GEO? 
-- Frank

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From: Doug Royer <[email-masked]>
Date: Tue, 22 Aug 2000 13:49:37 -0700

[email-masked] wrote:
> I seem to remember that the CGI, GKS, PHIGS computer graphics
> standards had a POLYGON_SET primitive. So maybe you don't really
> need the exception property?

Maybe - I have not seen one that allowed holes in the middle
of the polygon. Can you point me at something specific?
I'll start looking now.

> out if a coordinate is in the inside or outside of the set.

As the original person said ("JR" <[email-masked]>) most
are for 2-D. And since Columbus, the world ain't flat :-)
So independent of the algorithm needed. We need a way to
store the ever changing GEO data, which resulted in my proposal.
There is at least one supplier of this data on this WG list.

> But then, this would only require the CUA to convey to the
> CS a single LAT/LON coordinate (and a date/time value?) for the
> CS to calculate which set of time zones correspond to the GEO?

Yep, but as Burce and John have pointed out. Often the user
will have to choose when there is more than one VTIMEZONE
that matches.

-Doug

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From: John Stracke <[email-masked]>
Date: Wed, 23 Aug 2000 12:22:58 -0400

Doug Royer wrote:

> of the polygon.

A polygon with one hole in the middle can be expressed as the union of two
polygons with no holes.  (Side note to those who think I should be saying
"polygonal region" rather than "polygon": you're probably right.  :-)

For example, say you've got a large square with a small square hole in the
middle.  If you slice the figure in two, with a vertical line down the
middle, then you have two holeless polygons (one is a vertical rectangle with
two small rectangles sticking out to the right; the other is its mirror
image).

You can also come up with other partitions, of course.

--
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