[Auscope-geosciml] [SEC=UNCLASSIFIED]

Oliver.Raymond at ga.gov.au Oliver.Raymond at ga.gov.au
Mon Mar 1 22:40:11 EST 2010


Many thanks Alex and Simon.  That has cleared things up nicely.  Now I have to get my geophysicist to decide which option to take....

Regards,
Ollie

------------------------------------------------------------------------------------------------
Ollie Raymond
National Advice,  Maps and Standards Project
Geoscience Australia

Address: GPO Box 378, Canberra, ACT, 2601, Australia | ABN: 80 091 799 039
Ph: (02) 62499575 | Fax: (02) 62499992 | Email: Oliver.Raymond at ga.gov.au
Web:  http://www.ga.gov.au/minerals/research/national/nat_maps/nat_geol_maps.jsp<http://www.ga.gov.au/geoscience/national>

Google Map<http://maps.google.com/maps?f=q&hl=en&geocode=&q=canberra+australia&ie=UTF8&ll=-35.344028,149.158362&spn=0.007684,0.016404&t=h&z=17&iwloc=addr&om=1>

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-----Original Message-----
From: Simon Cox [mailto:simon.cox at jrc.ec.europa.eu]
Sent: Friday, 26 February 2010 9:47 PM
To: 'Robin, Alexandre'; Raymond Oliver
Cc: auscope-geosciml at lists.arcs.org.au
Subject: RE: [SEC=UNCLASSIFIED]

Very nice explanation Alex.

I would add just one point: if you expect that a CRS (whether geodetic or not) will be re-used, then it is good practice to 'register' it somewhere, and thus obtain an identifier that can be used to reference it. This strategy generally assists interoperability since it allows
(a) software developers to pre-configure applications to support registered CRSs, and
(b) data producers to refer to a pre-defined CRS using an identifier rather than by description (the latter makes comparison laborious and error prone).


--------------------------------------------------------
Simon Cox

European Commission, Joint Research Centre
Institute for Environment and Sustainability
Spatial Data Infrastructures Unit, TP 262
Via E. Fermi, 2749, I-21027 Ispra (VA), Italy
Tel: +39 0332 78 3652
Fax: +39 0332 78 6325
mailto:simon.cox at jrc.ec.europa.eu
http://ies.jrc.ec.europa.eu/simon-cox

SDI Unit: http://sdi.jrc.ec.europa.eu/
IES Institute: http://ies.jrc.ec.europa.eu/
JRC: http://www.jrc.ec.europa.eu/

--------------------------------------------------------



Any opinions expressed are personal unless otherwise indicated.


________________________________
From: Robin, Alexandre [mailto:Alexandre.Robin at spotimage.fr]
Sent: Friday, 26 February 2010 11:21
To: Oliver.Raymond at ga.gov.au; simon.cox at jrc.ec.europa.eu
Cc: auscope-geosciml at lists.arcs.org.au
Subject: RE: [SEC=UNCLASSIFIED]
Hello Oliver,

The main reason for the SWE Common vector is the management of CRS.
In GML, a vector is given as:


<gml:DirectionVector>
   <gml:vector srsName="#myLocalMagneticCRS">0.0 2.3 4.5</gml:vector>
</gml:DirectionVector>

You can see that it relies on a CRS defined externally, and this CRS must include the definition of units for each coordinate. This is a model that works well for geodetic CRS that are shared by many people but not necessarily for local CRS that are typically redefined for each problem. In SWE we thought that it is too constraining to force the definition of a new out-of-band CRS for each case.

Your example is a very good one where the projected quantity is not a distance and thus it is very unlikely that somebody else has already defined the exact same combination of spatial axes and magnetic field units.
For this reason, SWE does things slightly differently by relying on an external CRS or datum to define only an origin and axes directions in space (like it is usually done in physics) while units are defined inline in the vector instance. This is shown below:


<swe:Vector referenceFrame="#myLocalCRS" definition="urn:...:MagneticField">

   <swe:coordinate name="x">

      <swe:Quantity>

         <swe:uom code="T"/>

         <swe:value>0.0</swe:value>

      </swe:Quantity>

   </swe:coordinate>

   <swe:coordinate name="y">

      <swe:Quantity>

         <swe:uom code="T"/>

         <swe:value>2.3</swe:value>

      </swe:Quantity>

   </swe:coordinate>

   <swe:coordinate name="z">

      <swe:Quantity>

         <swe:uom code="T"/>

         <swe:value>4.5</swe:value>

      </swe:Quantity>

   </swe:coordinate>
</swe:Vector>

This obviously means that the same set of axes (usually Cartesian but not necessarily) can be reused for many different types of vectors. For instance a typical example in mechanics is to express location but also velocity and acceleration in the same reference frame. In GML this would mean defining a CRS for each of these, with the risk that the connection between them is lost (unless the same Datum is used perhaps), while in SWE Common the same frame is reused and only the units of the coordinates and the definition of the vector are adjusted.

Not that if efficient encoding is used, SWE Common also allows you to group several magnetic vector of this kind in an efficient CSV type block.

Hope this clarifies the matter...

Cheers,

-------------------------------------------------
Alexandre Robin
Spot Image, Web and E-Business
Tel: +33 (0)5 62 19 43 62
Fax: +33 (0)5 62 19 43 43
http://www.spotimage.com
Before printing, think about the environment


________________________________
De : Oliver.Raymond at ga.gov.au [mailto:Oliver.Raymond at ga.gov.au]
Envoyé : vendredi 26 février 2010 05:22
À : simon.cox at jrc.ec.europa.eu; Robin, Alexandre
Cc : auscope-geosciml at lists.arcs.org.au
Objet : [SEC=UNCLASSIFIED]

Hi Alex, Simon,

Could you give some advice please on the use of 'Vector' in GML and SensorML.  I am trying to model a measurement of remanent magnetisation, which involves a directed (vector) measurement of the magnetic field and need to know which one to use.

Was the SWE modelling team concerned that the GML Vector element could not handle all types of vectors?  Does the SWE Vector class supersede the GML Vector class, or is it designed for a different purpose?

Regards,
Ollie

------------------------------------------------------------------------------------------------
Ollie Raymond
National Advice,  Maps and Standards Project
Geoscience Australia

Address: GPO Box 378, Canberra, ACT, 2601, Australia | ABN: 80 091 799 039
Ph: (02) 62499575 | Fax: (02) 62499992 | Email: Oliver.Raymond at ga.gov.au
Web:  http://www.ga.gov.au/minerals/research/national/nat_maps/nat_geol_maps.jsp<http://www.ga.gov.au/geoscience/national>

Google Map<http://maps.google.com/maps?f=q&hl=en&geocode=&q=canberra+australia&ie=UTF8&ll=-35.344028,149.158362&spn=0.007684,0.016404&t=h&z=17&iwloc=addr&om=1>

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