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

[andy e]

Tim,

Nope, totally understand about wanting examples. Correct, ellipses/circles
on Earth. Unfortunately, can't give concrete examples in this setting, but
think along the lines of Circular Error (
http://en.wikipedia.org/wiki/Circular_error_probable), where, while you
have a center point, the "point" may be anywhere within the ellipse/circle.
A la polygons.
GPS error/accuracy is another valid use case, I would think.

Thanks,

Andy


On Fri, Nov 4, 2011 at 6:03 PM, Tim Schaub <tschaub at opengeo.org> wrote:

> Hey Andy,
>
> Maybe it would help sway the curve-haters if you could provide some
> ellipse examples.  Are we talking about ellipses on Earth?  Any links
> to pictures?
>
> Perhaps this one:
> http://maps.google.com/maps?ll=38.893956,-77.036503&z=18 (though I
> think you'd get more accuracy with a polygon)
>
> I'm not trying to be crass, I'm honestly interested.  I also know we
> didn't make this same request to proponents of the other geometry
> types.  Guess we all just bought into the point, line, poly (and
> multi-part cousins) without question.
>
> Tim
>
>
>
> On Fri, Nov 4, 2011 at 5:39 PM, andy e <virtualandy at gmail.com> wrote:
> > 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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> --
> Tim Schaub
> OpenGeo http://opengeo.org/
> Expert service straight from the developers.
>
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