Subject: Re: [Geopriv] The "geo" URI draft

From: "Alexander Mayrhofer" <[email-masked]>
Date: Wed, 3 Jun 2009 14:17:26 +0200

> >>If we want to go off planet, maybe we wont be
> >> able to take our geo: URIs with us.  I can live with that.
> 
> We can live with it, but why should we?

Let me rephrase that: We can either cover 99.9999% of the use cases
*without* adding extraterrestrial reference systems, or we can double to
complexity for 100% of the user base, for just satisfying an additional
0.0001% of the use cases.

Alex

---

From: "Carl Reed" <[email-masked]>
Date: Wed, 3 Jun 2009 09:20:10 -0600

Alex -

I concur. The OGC has had numerous discussions about planetary (non-earth) 
coordinate reference systems. These discussions were led by NASA and the 
USGS. At the end of the day, we decided that the planetary models are 
different enough from earth centric ones that the effort to enhance existing 
ISO, OGC, ITU, and IEC standards related to CRS requires additional 
consideration to properly extend the existing general reference model for 
spatial referencing by coordinates.

Regards

Carl

Also, for those interested, the following is the 2008 NASA position on the 
Lunar Coordinate System. Note the use of spherical coordinates. There is 
also something known as "mean sub-Earth point" which has no collorary to any 
earth CRS. These little details tend to be ignored by the geo-microformat 
community.
In the Lunar Coordinate System, planetocentric coordinates will be used. 
This approach, together with Cartesian coordinates, is now used in most 
planetary computations. These are right-handed spherical coordinates where 
the z-axis is the mean axis of rotation and the x-axis is the intersection 
of the Equator and the Prime Meridian. The x-axis is normal to the z-axis 
through the origin of the system, which is the Moon's center of mass. The 
y-axis is orthogonal to the x- and z-axes. Latitude is the angle between a 
line extending from the origin to the planetary equator and a vector from 
the origin to the point of interest. Longitude is the angle between this 
vector and the plane of the Prime Meridian measured in an eastern direction. 
Radius is the distance from Moon's center of mass to the point of interest.

----- Original Message ----- 
From: "Alexander Mayrhofer" <[email-masked]>
To: <[email-masked]>
Sent: Wednesday, June 03, 2009 6:17 AM
Subject: Re: [Geopriv] The "geo" URI draft

> _______________________________________________
> Geopriv mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/geopriv

---

From: Andy Mabbett <[email-masked]>
Date: Tue, 9 Jun 2009 13:17:58 +0100

In message <0061D732591640C2AC1B9A80EA083088@CarlandSusieOf>, Carl Reed 
<[email-masked]> writes

>The OGC has had numerous discussions about planetary (non-earth)
>coordinate reference systems.

>we decided that the planetary models are different enough from earth
>centric ones that the effort to enhance existing ISO, OGC, ITU, and IEC
>standards related to CRS requires additional consideration to properly
>extend the existing general reference model for spatial referencing by
>coordinates.

>Also, for those interested, the following is the 2008 NASA position on
>the Lunar Coordinate System.
[...]

All of which may be true (and is of interest to me, personally), but is 
a red herring so far as the applicability of GeoURI to non-terrestrial 
coordinates is concerned.

The usual reference scheme for the Moon has the location of the crater 
Mosting A at:

         geo:-0.7,5.9,ULCN2005

If a hypothetical second reference scheme, Foobar, has it at something 
as significantly different as, say:

         geo:33,88,Foobar

it matters not; the respective reference schemes will define what is 
meant by those figures; and if necessary, how to convert them.

All that a parser needs to know are the latitude & longitude values, and 
the scheme in use. My second example will be understood by any person, 
application or device which understands "Foobar", and will be 
interoperable between them; and between Foobar, ULCN2005 and any other 
scheme for which a conversion algorithm exists.

(Further more, nobody would sensibly try to convert them into to WGS84.)

This is no different to the same point on Earth being referred to as:

         52.548,-1.932,WGS84

and, by Ordnance Survey, as:

         404611,294504,OSGB

(both values can be seen on <http://is.gd/NuIo>)

-- 
Andy Mabbett