Evaluate the use of gml:EnvelopeWithTimePeriod when time axes are present

[Piero Campalani]

When a coverage contains a time axis, it might be convenient to display the BBOX through a ​gml:EnvelopeWithTimePeriod, to additionally specify the temporal extent with ISO timestamps.

A couple of things need to be evaluated before implementing it:

1. should the time period replace the lower/upper corner information of time numerical coordinates in the usual gml:Envelope ? (I suggest to keep both)
2. what happens if 2+ time axes are present? Which time axis should be taken? (I suggest we use gml:EnvelopeWithTimePeriod only when 1 and only 1 time axis is found in the dimensions of the (output) CRSs)

[Peter Baumann]

FYI, Max Martinez has suggested this roadmap once which GMLCOV development has followed in its development:

Establish WCS Extension adding a CRS GetCoverage request parameter + provision of CRSs supported in the Capabilities document.
Complete replacement of 07-092r3 through creation of an OGC-NA Name Type Specification (NTS) for predefined, combined, and parameterized CRSs to augment the /def/ NTS (which defines http URIs for standard CRS).
Devise AUTO CRS definitions.
Specification of CRS registry service (cf. WCTS).
CR to GML: EnvelopeWithCRSType (similar to EnvelopeWithTimePeriodType).

…are we approaching the last step now?

[Piero Campalani]

A possible solution (eg called gml:EnvelopeByAxisType):

  <gml:EnvelopeByAxis srsDimension=4
       axisLabels="Lat Long h unix"
       uomLabels="degree degree m s"
       srsName="http://www.opengis.net/def/crs-compound?
                1=http://www.opengis.net/def/crs/EPSG/0/4327&
                2=http://www.opengis.net/def/crs/OGC/0/UnixTime">
     <gml:crsAxis axisLabel="Lat" uomLabel="degree">
       <gml:lowerBound>40</gml:lowerBound>
       <gml:upperBound>45</gml:upperBound>
     </gml:crsAxis>
     <gml:crsAxis axisLabel="Long" uomLabel="degree">
       <gml:lowerBound>10</gml:lowerBound>
       <gml:upperBound>15</gml:upperBound>
     </gml:crsAxis>
     <gml:crsAxis axisLabel="h" uomLabel="m">
       <gml:lowerBound>20</gml:lowerBound>
       <gml:upperBound>50</gml:upperBound>
     </gml:crsAxis>
     <gml:crsAxis axisLabel="unix" uomLabel="s">
       <gml:lowerBound>978303600</gml:lowerBound>
       <gml:upperBound>1291158000</gml:upperBound>
       <gml:beginPosition>2001-01</gml:beginPosition>
       <gml:endPosition>2010-12</gml:endPosition>
     </gml:crsAxis>
  </gml:EnvelopeByAxis>

The xsd would be kind of:

 <!-- CRSAxisExtentType -->
 <complexType name="CRSAxisExtentType">
   <sequence>
     <element name="lowerCorner" type="xsd:double"/>
     <element name="upperCorner" type="xsd:double"/>
     <sequence minOccurs="0">
       <element name="beginPosition" type="gml:TimePositionType"/>
       <element name="endPosition"   type="gml:TimePositionType"/>
     </sequence>
   </sequence>
   <attribute name="axisLabel" type="xsd:NCName"/>
   <attribute name="uomLabel"  type="xsd:NCName" minOccurs="0"/>
 </complexType>
 <!-- EnvelopeByAxisType -->
 <complexType name="EnvelopeByAxisType">
   <sequence maxOccurs="unbounded">
     <element name="crsAxis" type="gml:CRSAxisExtentType"/>
   </sequence>
   <attributeGroup ref="gml:SRSReferenceGroup"/>
 </complexType>
 <element name="EnvelopeByAxis" type="gml:EnvelopeByAxisType"
          substitutionGroup="gml:AbstractObject"> 

An additional schematron could also let gml:TimePositionType extensions only if the related CRS is temporal.

[Peter Baumann]

next version: some redundancy removed; better time CRS name (not important); ISO 8601 time coordinates; "Corner" → "Bound" in xsd; choice of time / space; etc:

  <gml:EnvelopeByAxis srsDimension="4"
       axisLabels="Lat Long h unixtime"
       uomLabels="degree degree m s"
       srsName="http://www.opengis.net/def/crs-compound?
                1=http://www.opengis.net/def/crs/EPSG/0/4327&
                2=http://www.opengis.net/def/crs/OGC/0/UnixTime">
     <gml:crsAxis axisLabel="Lat">
       <gml:startPos>40</gml:lowerBound>
       <gml:endPos>45</gml:upperBound>
     </gml:crsAxis>
     <gml:crsAxis axisLabel="Long">
       <gml:startPos>10</gml:lowerBound>
       <gml:endPos>15</gml:upperBound>
     </gml:crsAxis>
     <gml:crsAxis axisLabel="h">
       <gml:startPos>20</gml:lowerBound>
       <gml:endPos>50</gml:upperBound>
     </gml:crsAxis>
     <gml:crsAxis axisLabel="unixtime">
       <gml:startTime>2001-01</gml:beginPosition>
       <gml:endTime>2010-12</gml:endPosition>
     </gml:crsAxis>
  </gml:EnvelopeByAxis>

The xsd would be kind of:

 <!-- CRSAxisExtentType -->
 <complexType name="CRSAxisExtentType">
   <sequence>
     <choice>
       <sequence>
         <element name="startPos" type="xsd:double"/>
         <element name="endPos"   type="xsd:double"/>
       </sequence>
       <sequence>
         <element name="startTime" type="gml:TimePositionType"/>
         <element name="endTime"   type="gml:TimePositionType"/>
       </sequence>
     <choice>
   </sequence>
   <attribute name="axisLabel" type="xsd:NCName"/>
 </complexType>
 <!-- EnvelopeByAxisType -->
 <complexType name="EnvelopeByAxisType">
   <sequence maxOccurs="unbounded">
     <element name="crsAxis" type="gml:CRSAxisExtentType"/>
   </sequence>
   <attributeGroup ref="gml:SRSReferenceGroup"/>
 </complexType>
 <element name="EnvelopeByAxis" type="gml:EnvelopeByAxisType"
          substitutionGroup="gml:AbstractObject"> 

This still is limited: once we will have ordinal names, such as "red", "green", "blue" this won't work again. I am still for full generality = strings in coordinates, together with xsd or schematron rules for the proper syntax. The original problem in GML with strings originated from a sloppy modelling (several coordinate items in one element, whitespace separated - instead of isolation in separate elements) which has been remedied here.

[Peter Baumann]

superseded by CIS 1.1 which can handle multiple time axes etc.