[Seavox] Vertical CRS

[Woolf, A (Andrew)]

I think it's important that your ontology be able to map onto the ISO
standard for CRS (ISO 19111), which it more-or-less does.

To review the standard... In summary, it says a CRS consists of:
 (0) general CRS attributes, e.g. CRS name
 (1) a "Coordinate System" (consisting of CS name etc. and an ordered
list of {axis name, axis units, axis direction} triples, one per CS
axis) - for a vertical CS we only have one axis
 (2) a "Datum" tying the CS to the real world. In conventional geodesy
gives the parameters of a reference ellipsoid for example (so a lat,lon
then has an actual position in space), but for our vertical CRS it would
be things like 'zero at LAT'. Of course LAT then needs definition, and
the whole question of how to deal with parametric vertical coordinates
is the subject of a new revision of ISO 19111. Until it's resolved, I
think an ad-hoc treatment of Datum for such CRS is perfectly reasonable
(and probably wise).

So in your example below, we'd have:
 * CS:
  - name not explicit, could be autogenerated (e.g. DepthCS)
  - one vertical axis (implied)
  - axis name: 'Depth'
  - axis units (measuredIn): metres
  - axis direction (directionIs): down
 * CRS:
  - general attributes (e.g. name) are not explicit, a name could be
autogenerated (e.g. DepthFromMeanSeaLevelCRS)
  - CS is implied ('DepthCS')
  - Datum (datumIs): mean_sea_level 

> -----Original Message-----
> From: seavox-bounces at biwebs1.nerc-liv.ac.uk 
> [mailto:seavox-bounces at biwebs1.nerc-liv.ac.uk] On Behalf Of Roy Lowry
> Sent: 19 January 2007 13:24
> To: seavox at biwebs1-2.nerc-liv.ac.uk
> Subject: [Seavox] Vertical CRS
> 
> Dear All,
> 
> I am about to embark on setting up some vocabularies to 
> support vertical co-ordinate reference systems.  The first 
> stage - needed for a number of purposes - is to set up a 
> series of terms for vertical CRS datums appropriate to 
> conventional distance measurements (Lowest Astronomical Tide 
> and so on), which I'll circulate for comment in the next week or so.  
> 
> I'm also thinking about sibling lists for other units that 
> are going through the ISO acceptance process like pressure 
> and density.  Any suggestions for populating these are welcome.
> 
> Given these, simple vocabularies for directionality (e.g. 
> height is up, depth is down), vertical CRS names and units 
> (BODC-biased version already there, but something like 
> UDUNITS might be more acceptable) provides the basis in the 
> Vocabulary Server for a vertical CRS ontology based on RDF 
> triples like:
> 
> Depth measuredIn metres
> Depth datumIs mean_sea_level
> Depth directionIs down
> 
> Any comments on how this could be improved within the 
> constraints of the vocabulary server design would be welcomed.
> 
> Cheers, Roy.
> 
> 
> 
> 
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