Re: [ontolog-forum] Fw: GPS coordinates in an ontology?

[Toby Considine <Toby.Considine@xxxxxxxxx>]

Ontologies are about higher order interoperability. This, as observed above, requires at least an acknowledgement of the context.

I would look generally to the work of open geospatial consortium (ogc ), not only for the information models and specifications,  but for the large scale interop demos which are very informative and mind stretching.

Tc

On Oct 26, 2010 7:47 AM, "Chris Partridge" <partridge.csj@xxxxxxxxx> wrote:
> Hi,
>
> Ian mentions below I had done some work in this area.
>
> As Sean said earlier, it is useful to distinguish between the object being
> represented and its representation.
> As Ian points out below, it can take some effort to be sure what object is
> being presented.
>
> The team found that it is often geo-spatial (all three dimensions) and
> temporal data - rather than just spatial data that is of interested (at
> least in the defence domain we were working in). We are often interested in
> the things that stay in the same place (place? See Aristotle for more
> details) over time.
> Maybe because we have a 4D bias :-) we found a 4D approach useful.
> I give some pointers to the 4D approach below.
> A geo-spatial (all three dimensions) and temporal position (point) is a
> point in 4D.
> So (as Ian says below) if we were not interested in the temporal co-ordinate
> - in programming terms, it was stripped out - then we have a point in 3D
> (with an associated time) and a line in 4D.
> If (as Ian says below) we were not interested in the altitude co-ordinate -
> in programming terms, it was stripped out - then we have a line in 3D (with
> an associated time) and 4D.
> There were the standard issues about whether the line was the tangent to the
> normal of some reference ellipsoid or through some notional centre of the
> earth.
> If we were not interested in either the altitude or temporal co-ordinates,
> then we have a line in 3D and a plane in 4D.
>
> Interestingly we found that taking the 4D approach revealed some potential
> improvements in airspace management.
> We were interested and amused to find the term 4DATM (4D Air Traffic
> Management) is in use - whereas from our perspective this follows the
> traditional 3D + 1 approach (i.e. it is not 4D in our sense of the word).
> Our take on this was that this recognised the importance of looking at space
> and time together (for things like ATM) but did not make the (paradigm?)
> shift from 3D + 1 to 4D.
>
> Regards,
> Chris
>
>> -----Original Message-----
>> From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx [mailto:ontolog-forum-
>> bounces@xxxxxxxxxxxxxxxx] On Behalf Of Ian Bailey
>> Sent: 26 October 2010 11:58
>> To: '[ontolog-forum] '
>> Subject: Re: [ontolog-forum] Fw: GPS coordinates in an ontology?
>>
>> Hello,
>>
>> GPS coordinates aren't simple lat-long, although some systems simply
>> calculate these from raw GPS data and discard the rest. The transmissions
>> from the satellites can also be used to derive a temporal measure (the UTC
>> time) and an altitude measure (from centre of the reference geoid). It may
>> be that some systems only care about the point on the surface of the
> earth,
>> and ignore the other aspects.
>>
>> Depending on the intended use, a system might use just the derived
> lat-long,
>> in which case it represents a line extending from the centre of the Geoid
> (or
>> reference ellipsoid) rather than a point on or above it.
>>
>> Even when the system has an interest in the altitude, it's still not
> simple.
>> In some exotic cases they may use specialist reference ellipsoids to
> estimate
>> the distance above the surface of the earth. If two systems use different
>> ellipsoids, you've got problems.
>>
>> There is another interpretation I've seen, which is a consequence of the
>> accuracy of GPS. Sometimes, the coordinates provided are intended to refer
>> to an area centred on the point on or above the surface of the ellipsoid
>> whose radius is given by the tolerance of the GPS system. That gets even
>> more complex when landscape is taken into account. Not only does a
>> mountain alter the shape of the tolerance area, but it may also block some
>> satellite signals and so reduce accuracy of the GPS reading, which can
> make
>> the area larger. Chances are that if the mountain is small and pointy, it
>> won't be very well represented by the reference ellipsoid, which is
> another
>> added complication.
>>
>> A third case is the combination of the above where altitude and accuracy
>> come together, and the GPS coordinates actually represents a cone (or more
>> complex shape if mountains, buildings, etc. interfere) where the pointy
> end
>> is at the centre of the Geoid.
>>
>>
>> Chris Partridge has done a lot of work in this area, also looking at other
>> coordinate systems than GPS - e.g. UK and US grid references.
>>
>> So, Sean and David's comments about what the coordinates refer to is
>> absolutely. When dealing with coordinates, if you don't understand the
>> frame of reference being used, the "real-world" semantics of the
> coordinates
>> cannot be properly ascertained. None of this matters in a lab, but it can
> be a
>> bit of a problem when you're using the coordinates from different systems
>> (with different intended references) to de-conflict commercial airspace or
>> drop a 1000lb bomb.
>>
>>
>> Ian
>>
>> -----Original Message-----
>> From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
>> [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of David Leal
>> Sent: 25 October 2010 22:24
>> To: [ontolog-forum]
>> Subject: Re: [ontolog-forum] Fw: GPS coordinates in an ontology?
>>
>> Dear Sean,
>>
>> I agree with you when you say:
>> > It may be worth considering separating out the concept of position
>> > from
>> the
>> >representation of position, to allow for position to be represented
>> >using multiple co-ordinate systems or geographic regions.
>>
>> We must remember that WGS84 does two things - it defines a geometric
>> space (within which the earth is more or less at rest), and it defines a
>> coordinate system for identifying points within it.
>>
>> TAI (International Atomic Time) is analogous - it defines a temporal space
>> (defined by a set of clocks at particular positions within the earths
>> gravitational field), and it identifies instants within it.
>>
>> Best regards,
>> David
>>
>> At 20:22 25/10/2010, you wrote:
>>
>> > The problem is not just to record co-ordinates, but to do something
>> >with them. This means identifying services that can evaluate poistion
>> >functions, such as computing proximity, comparing regions, converting
>> >between co-ordinates and place names, or following through the
>> >hierarchy of administrative districts.
>> >
>> > Also, given that there are a large number of co-ordinate systems
>> >actually in use (often based on different shapes for the Earth), there
>> > will also be a requirement for services to convert between different
>> >co-ordinate systems.
>> >
>> > It may be worth considering separating out the concept of position
>> > from
>> the
>> >representation of position, to allow for position to be represented
>> >using multiple co-ordinate systems or geographic regions.
>> >
>> >
>> > Sean Barker
>> >Bristol, UK
>> >
>> >
>> > > -----Original Message-----
>> > > From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
>> > > [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of John F.
>> > > Sowa
>> > > Sent: 25 October 2010 14:20
>> > > To: ontolog-forum@xxxxxxxxxxxxxxxx
>> > > Subject: Re: [ontolog-forum] GPS coordinates in an ontology?
>> > >
>> > >
>> > > *** WARNING ***
>> > >
>> > > This message has originated outside your organisation, either from
>> > > an external partner or the Global Internet.
>> > > Keep this in mind if you answer this message.
>> > >
>> > >
>> > > On 10/25/2010 8:48 AM, Joshua Lieberman wrote:
>> > >> Depending on the required precision, GPS coordinates may or may not
>> > >> be
>> > >
>> > >> something to enshrine in a static ontology, and a GPS point may or
>> > >> may
>> > >
>> > >> not be the appropriate geometric representation.
>> > >
>> > > I strongly agree.
>> > >
>> > > Every application is likely to need other domain-dependent
>> > > representations, such as a street address. And it is also likely to
>> > > need various transformations, such as deriving speed down those
>> > > roads and streets.
>> > >
>> > > All the units of measure are interrelated, and the ontology should
>> > > include all of them.
>> > >
>> > > John
>> > >
>> >
>> >
>> >
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>>
>> ============================================================
>> David Leal
>> CAESAR Systems Limited
>> registered office: 29 Somertrees Avenue, Lee, London SE12 0BS registered
> in
>> England no. 2422371
>> tel: +44 (0)20 8857 1095
>> mob: +44 (0)77 0702 6926
>> e-mail: david.leal@xxxxxxxxxxxxxxxxxxx
>> web site: http://www.caesarsystems.co.uk
>> ============================================================
>>
>>
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