[Requests] Request for Comments (10-034r3)

Johannes Echterhoff johannes.echterhoff at igsi.eu
Fri Jul 16 08:02:09 EDT 2010


PART A


1. Evaluator: Johannes Echterhoff, International Geospatial Services
Institute GmbH

2. Submission: OGC 10-034r3 - OGC MovingObjectSnapshot



PART B.1

1. Requirement: General

2. Implementation Specification Section number: 5.2, 6

3. Criticality: Major

4. Comments/justifications for changes: 

The first paragraph states that "The coordinates in the GML Point Profile
are defined in a coordinate reference system known as EPSG:4326 ...". We
could only find the "GML Point Profile" in pending docs - OGC 10-071r2. In
that document, it is not clear if EPSG:4326 is the only allowed SRS to be
used to provide point locations in. It only states that "Any consumer of
data instances compliant with this profile shall be able to interpret the
following OGC URN urn:ogc:def:crs:EPSG::4326" - which sounds like EPSG:4326
is the default SRS (although that is not stated in 10-071r2) but that other
SRSs are allowed. Whether EPSG:4326 is the default and / or only allowed SRS
should be clearly defined in OGC 10-071 - or in 10-034 if that is intended
to make the according constraint.

The example given in section 6 shows a position with a gml:Point without
srsName attribute - would that mean that EPSG:4326 should be assumed as
default? 


PART B.2

1. Requirement: General

2. Implementation Specification Section number: 5.2

3. Criticality: Editorial

4. Comments/justifications for changes: The last paragraph states that
"Elevation is defined separate from the point location in
latitude-latitude". This should probably say "... latitude-longitude".


PART B.3

1. Requirement: General

2. Implementation Specification Section number: General

3. Criticality: Major

4. Comments/justifications for changes: The application schema depends upon
the "GML Point Profile". However, for expressing the timeStamp property of a
MovingObjectSnapshot it uses a gml:TimeStamp as-is. The example in section 6
appears to be simple in that it uses an ISO 8601 date time with GMT/Zulu
timezone. But a gml:TimeInstant can be much more complex. So is the
intention to not restrict the contents of the gml:TimeInstant? If yes, is
another "GML Time Instant Profile" envisaged? A simple alternative would be
to just use "DateTime" as the type of the MovingObjectSnapshot.timeStamp
property. According to GML 3.2.1 this is a valid type to be used in the
conceptual model and would map to xs:dateTime in the XSD implementation.
This would be very simple - although the restriction to one specific
timezone is not made, afaik. Not sure if that should be required.


PART B.4

1. Requirement: General

2. Implementation Specification Section number: General

3. Criticality: Major

4. Comments/justifications for changes: Why is there no conceptual model for
the MovingObjectSnapshot type? If this type is to be reused by other GML
application schema, the conceptual model should be included in the standard,
not only the XSD implementation of it. The general requirements concerning
the usage of the MovingObjectSnapshot (e.g. that the speed property shall be
given in meters per second) should then be made with respect to this
conceptual model.


PART B.5

1. Requirement: General

2. Implementation Specification Section number: 7

3. Criticality: Minor

4. Comments/justifications for changes: The XSD uses 'must' instead of
'shall' in annotations - this should be changed. Also, the annotation of the
timeStamp element seems to be wrong - it currently reads "value is a GML
point". The annotation should be updated properly.


PART B.6

1. Requirement: General

2. Implementation Specification Section number: 7

3. Criticality: Major

4. Comments/justifications for changes: If MovingObjectSnapshot is a GML
feature, then why does the schema not include a
MovingObjectSnapshotPropertyType complexType? This would be needed by GML
application schema that want to include MovingObjectSnapshot and encode this
using the inlineOrByReference pattern. Simply include the following XML
snippet in the schema:

  <complexType name="MovingObjectSnapshotPropertyType">
    <sequence minOccurs="0">
      <element ref="mos:MovingObjectSnapshot"/>
    </sequence>
    <attributeGroup ref="gml:AssociationAttributeGroup"/>
    <attributeGroup ref="gml:OwnershipAttributeGroup"/>
  </complexType>


----------------------------------------------
Johannes Echterhoff
Project Manager
International Geospatial Services Institute GmbH
Werner-Heisenberg-Strasse 73 
D-26723 Emden, Germany
phone: +49.4921.94.14.03
mobile: +49.179.480-8931
 
www.igsi.eu 
johannes.echterhoff at igsi.eu
 
Company Register: HRB 200520, Amtsgericht Aurich 
Executive Directors: Martin Klopfer & Dr. Ingo Simonis 







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