[Geojson] circles (was: Toward consensus on proposals)

[andy e]

Thanks for the discussion/feedback on circles/ellipses. Sorry for not
responding sooner (been busy trying to work up a proposal that will get us
more time with these very circles/ellipses :) ). Also wanted to talk with
coworkers about this.

To reiterate what Sean has stated, the inclusion of circles and ellipses is
to support raw geometries and not queries/relationships/features. The data
that we are handling is purely just that - a circle or ellipse with a
radius/axii (typically in meters) and in the case of ellipses, a rotation
(typically in degrees). To be honest, Ellipses are much more important to
us than Circles, but I threw that in as "Just use a even Ellipse for a
Circle" seemed like a cop-out. I did not realize GML supported Ellipses, so
I will try to make the change to the spec to line that up.

In regards to units, in other specs, if a "unit" is not widely
standardized, it is defined by the requestor/provider. Take HTTP and
Content-Type (http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html),
where they specify "Content-Type" : " text/html ..."
That was my intention here - to clear up any possible confusion, specify
the units. As mentioned (by Tim S and others, sorry, forgetting right now),
the problem with keeping units in the CRS occurs when you start specifying
geoms in lat/lon. Radians and CRS conversions are not very intuitive for
those without strong GIS backgrounds (like myself).

I would be okay with defaulting to CRS if no units were specified (or vice
versa with meters). Hence the option of using that field.

I realize it is somewhat repetitive/complex, but given that no one seems to
be using Circles/Ellipses anyway, maybe it just won't show up that often. :)

With regards to GEOS and JTS, I understand the concern, but wonder if we
should even think about implementation when defining the spec. As
previously mentioned, it is likely that even we will just store
Ellipses/Circles this way and convert to approximate polygons when
processing.

Thanks to my co-worker Nathan for input here.

Andy

On Fri, Nov 4, 2011 at 7:29 AM, <christopher.schmidt at nokia.com> wrote:

>
> On Nov 4, 2011, at 5:13 AM, ext Martin Daly wrote:
>
> >> I propose that we accept or reject the Circle/Ellipse proposal without
> >> getting too caught up in the units details right now. If it can't be
> >> solved and stalls out we can terminate it then. How does that sound?
> >
> > I hate curves as much as, if not more than, the next person, but I can
> see that a compact representation of a circle would be useful for some
> situations.
> >
> > Also, while not exactly a precedent, we already have "bbox" as a compact
> representation of a rectangular polygon, albeit restricted to the "Feature"
> and "FeatureCollection" objects.
>
> BBOX is not a representation of a geometry. It's a piece of metadata about
> a feature
> or FeatureCollection. It doesn't replace a geometry.
>
> -- Chris
>
> >
> > Martin
> >
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