Fwd: Simplified XML schema for GML

["Ram Kumar" <kumar.sydney@gmail.com>]

---------- Forwarded message ----------
From: Carl Reed OGC Account <creed@opengeospatial.org>
Date: Nov 17, 2006 9:22 AM
Subject: Re: Simplified XML schema for GML
To: Ram Kumar <kumar.sydney@gmail.com>

Ram -

 

Sorry for the delay. Funny - or serendipic - that there is a similar discussion going on in the IETF regarding dynamic features, tracking, the meaning of bearing/distance and so forth.

 

Anyway, there is a bunch of stuff in GML that can be used for expressing the information you have specified below.

 

In terms of the coordinate reference system, since the xAL spec is working with only latitide-longitude, this does limit the number of possibilities. There are two approaches: using urn:ogc etc or XML schema. There is an approved OGC XML schema for expressing geographics. I have copied a section from one of the OGC standards documents. As this is a complete enumeration, the XML code is a bit long :-) Now, this schema follows the rules for expressing a geographic CRS as defined in the EPSG 6.0 database. EPSG is viewed by the geospatial community as a normative reference for expressing a CRS. Even CAP references EPSG 6.0 for the normative expression of what is meant by geographic WGS 84.

 

In terms of the actual lat/long, that is pretty straight forward. This includes expressing the direction. For example:

 

<gml:Point srsName="urn:ogc:def:crs:EPSG:6.6:4326">

<gml:pos>45.256 -110.45</gml:pos>

</gml:Point>

This example is from the OGC GML Point Profile spec. Notice that the CRS is expressed as a urn. Now, as part of the schema for this point profile, it is possible to also express feature properties, such as direction. As to how to do this, I would need to double check.

 

Also, this expression for a point feature is identical to that used in GeoRSS and the latest version of the GML Profile for OASIS. The OGC point profile document can be found at http://portal.opengeospatial.org/files/?artifact_id=11606

 

Cheers

Carl

 

When using this GML 3.1.1 profile, the definition of each Geographic coordinate reference system (CRS) shall be XML encoded using the GeographicCRS element, defined in the attached normative XML Schema Document named coordinateReferenceSystems.xsd. The GML objects contained or referenced in this GeographicCRS are indicated in this XML document skeleton:

<GeographicCRS>

   <usesEllipsoidalCS>

      <EllipsoidalCS>

         <usesAxis> (two or three)

            <CoordinateSystemAxis></CoordinateSystemAxis>

         </usesAxis>

         <usesAxis>

            <CoordinateSystemAxis></CoordinateSystemAxis>

         </usesAxis>

      </EllipsoidalCS>

   </usesEllipsoidalCS>

   <usesGeodeticDatum>

      <GeodeticDatum>

         <usesPrimeMeridian>

            <PrimeMeridian></PrimeMeridian>

         </usesPrimeMeridian>

         <usesEllipsoid>

            <Ellipsoid></Ellipsoid>

         </usesEllipsoid>

      </GeodeticDatum>

   </usesGeodeticDatum>

</GeographicCRS>

 

NOTE 1       The UML class diagrams contained in Subclause C.2 provide graphical views of the contents of the GeographicCRS XML element.

This skeleton XML document indicates that:

a)      A GeographicCRS element shall contain one usesEllipsoidalCS and one usesGeodeticDatum elements (in addition to other mandatory and optional information).

b)      That usesEllipsoidalCS element shall reference or contain the definition of one EllipsoidalCS.

c)      That EllipsoidalCS definition element shall contain an ordered sequence of two or three usesAxis elements.

d)      Each of those usesAxis elements shall reference or contain the definition of one CoordinateSystemAxis. The referenced or listed axis order shall be used for position coordinates in that GeographicCRS, with the specified units and directions of each axis.

NOTE 2       The two axes of a GeographicCRS are usually named geodetic latitude and geodetic longitude, with coordinates listed in that order and with both latitude and longitude values given in decimal degrees.

e)      That usesGeodeticDatum element shall reference or contain the definition of one GeodeticDatum.

f)        That GeodeticDatum definition element shall contain one usesPrimeMeridian and one usesEllipsoid elements

g)      That usesPrimeMeridian element shall reference or contain the definition of one PrimeMeridian.

h)      That usesEllipsoid element shall reference or contain the definition of one Ellipsoid.

1.1               XML document full example

An example XML document completely defining a GeographicCRS is:

<?xml version="1.0" encoding="UTF-8"?>

<GeographicCRS xmlns="http://www.opengis.net/gml " xmlns:gml="http://www.opengis.net/gml" xmlns:xlink=" http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance " xsi:schemaLocation="http://www.opengis.net/gml ../commonCRSsProfile.xsd" gml:id="EPSG4277">

   <!-- Primary editor: Arliss Whiteside. Last updated 2005-10-05-->

   <srsName>OSGB 1936</srsName>

   <srsID>

      <name codeSpace="urn:ogc:def:crs:EPSG:6.0:">4277</name>

   </srsID>

   <usesEllipsoidalCS>

      <EllipsoidalCS gml:id="EPSG6402">

         <csName>ellipsoidal</csName>

         <csID>

            <name codeSpace="urn:ogc:def:cs:EPSG:6.0:">6402</name>

         </csID>

         <usesAxis>

            <CoordinateSystemAxis gml:id="EPSG9901" gml:uom="urn:ogc:def:uom:OGC:0.0:degree">

               <name>Geodetic latitude in north direction with degree units</name>

               <axisID>

                  <name codeSpace="urn:ogc:def:axis:EPSG:6.0:">9901</name>

               </axisID>

               <axisAbbrev>Lat</axisAbbrev>

               <axisDirection>north</axisDirection>

            </CoordinateSystemAxis>

         </usesAxis>

         <usesAxis>

            <CoordinateSystemAxis gml:id="EPSG9902" gml:uom="urn:ogc:def:uom:OGC:0.0:degree">

               <name>Geodetic longitude in east direction with degree units</name>

               <axisID>

                  <name codeSpace="urn:ogc:def:axis:EPSG:6.0:">9902</name>

               </axisID>

               <axisAbbrev>Lon</axisAbbrev>

               <axisDirection>east</axisDirection>

            </CoordinateSystemAxis>

         </usesAxis>

      </EllipsoidalCS>

   </usesEllipsoidalCS>

   <usesGeodeticDatum>

      <GeodeticDatum gml:id="EPSG6277">

         <datumName>OSGB 1936</datumName>

         <datumID>

            <name codeSpace="urn:ogc:def:datum:EPSG:6.0:">6277</name>

         </datumID>

         <usesPrimeMeridian>

            <PrimeMeridian gml:id="EPSG8901">

               <meridianName>Greenwich</meridianName>

               <meridianID>

                  <name codeSpace="urn:ogc:def:meridian:EPSG:6.0:">8901</name>

               </meridianID>

               <greenwichLongitude>

                  <angle uom="urn:ogc:def:uom:OGC:1.0:degree">0</angle>

               </greenwichLongitude>

            </PrimeMeridian>

         </usesPrimeMeridian>

         <usesEllipsoid>

            <Ellipsoid gml:id="EPSG7001">

               <ellipsoidName>Airy 1830</ellipsoidName>

               <ellipsoidID>

                  <name codeSpace="urn:ogc:def:ellipsoid:EPSG:6.0:">7001</name>

               </ellipsoidID>

               <semiMajorAxis uom="urn:ogc:def:uom:OGC:1.0:meter">6377563.396</semiMajorAxis>

               <secondDefiningParameter>

                  <inverseFlattening uom="urn:ogc:def:uom:OGC:1.0:unity">299.3249646</inverseFlattening>

               </secondDefiningParameter>

            </Ellipsoid>

         </usesEllipsoid>

      </GeodeticDatum>

   </usesGeodeticDatum>

</GeographicCRS>

 

NOTE          This example XML document can be used as a template, and edited to produce definitions of other GeographicCRSs.

----- Original Message -----

From: Ram Kumar

To: Carl Reed OGC Account

Sent: Tuesday, November 07, 2006 3:16 AM

Subject: Re: Simplified XML schema for GML

 

Hi Carl,

 

The description:

 

-An identifier for the location system used

-The measure of latitude in degrees

-The measure of latitude in minutes

-The direction of latitude measurement offset from the equator

-The measure of longitude in degrees

-The measure of longitude in minutes

-The direction of longitude measurement offset from the meridian

 

Regards,

 

Ram

 

On 11/3/06, Carl Reed OGC Account <creed@opengeospatial.org > wrote:

Ram -

 

Glad to see that you incorporate CRS metadata! I tried to get the EM TC to do the same for CAP and EDXL and got absolutely nowhere. Too US centric. But that is a different story.

 

You are correct in your initial assessment.

 

Before moving forward, could you provide a description of what you mean by "measure" and what is meant by "direction". I think I know but I want to make sure we are semantically on the same page.

 

Regards

 

Carl

 

----- Original Message -----

From: Ram Kumar

To: Carl Reed OGC Account

Sent: Wednesday, November 01, 2006 9:34 PM

Subject: Re: Simplified XML schema for GML

 

Hi Carl,

 

We are after some an OGC specified schema that contains the following or similar

elements to support a physical address:

-coordinate system code
-latitude degrees measure
-longitude degrees measure
-latitude minutes measure
-longitide degrees measure
-latitude direction
-longitude direction

 

Which of your schemas that you have supports the above and we just want to reuse them.

I do not think the simple profile schema you suggested has any of these. The above are

the basic stuff generally used to represent an address location.

 

Regards,

 

Ram

 

On 11/2/06, Ram Kumar <kumar.sydney@gmail.com > wrote:

Hi Carl,

 

Thanks. Do you mean to say that we can use the GML simple features profile for

commonly used geocoding information such as latitude, longitude, directions? We

need these basic stuff only to represent address coordinates.

 

Regards,

 

Ram

 

On 11/1/06, Carl Reed OGC Account <creed@opengeospatial.org > wrote:

Hi Ram -

 

Sukumar posted the latest draft of the GML OASIS Profile into the document archives for the EM TC. As I am not sure of all the requirements for a simple XML Schema for GML that CIQ can use, there is also another GML profile called GML simple features profile. Much more extensive than the very limited one for OASIS but still way smaller than full GML.

 

Regards

Carl

 

----- Original Message -----

From: Ram Kumar

To: Carl Reed OGC Account

Sent: Tuesday, October 31, 2006 1:55 PM

Subject: Simplified XML schema for GML

 

Hi Carl,

 

Any news about the availability of the simple XML Schema for GML that CIQ can use?

 

Regards,

 

Ram