Vertical Extent ★★★

To quickly determine the general location of features included in an identified resource it is useful that the extent information include any descriptions vertical extents.


Element Name	verticalElement
Parent	MD_Metadata.identificationInfo>MD_Identification.extent
Class/Type	EX_VerticalExtent
Purpose	Discovery
Audience	machine resource - ⭑ ⭑ ⭑ ⭑
	general - ⭑ ⭑ ⭑ ⭑
	resource manager - ⭑ ⭑
	specialist - ⭑ ⭑ ⭑ (higher if domain specific time periods are used)
Metadata type	descriptive
ICSM Level of Agreement	⭑ ⭑ ⭑

Definition

Provides vertical component of the extent of the resource to aid discovery.

ISO Obligation

There can be zero to many [0..*] verticalElements packages for the cited resource in the Resource Extent package of class EX_VerticalExtent for a resource cited in a metadata record.

Discussion

Every metadata record describing resources which contain height or depth information should describe the limits of that extent. These extents descriptions should include units of measure and other information so that those searching for resources can be provided with a quick idea of the vertical range of the resource.

The use of multiple vertical extents is useful for describing more complicated resources.

Best Practice Recommendations

Therefore - it is strongly recommended that to support the discovery of resources, every metadata record contains, as needed vertical extent description of the resource area of interest. Capture the units of measure and the datum used.

The MDWG recommends, when the heights and depths of a resource are important to the resource, populating as many instances of Vertical Extent packages as needed to give a common understanding of the depth and elevation coverage of the cited resource.

Recommended Sub-Elements

minimumValue - (type - Real) The minimum vertical extent to which the resource is designed to be used
maximumValue - (type - Real) The maximum vertical extent to which the resource is designed to be used
verticalCRSId - (class - SC_VerticalCRS ) Identifies the vertical coordinate reference system used for the minimum and maximum values

Also Consider

EX_Extent The class that contains all extent information about the cited resource - vertical, geographical or temporal.
EX_GeographicExtents is an abstract class that can be express three ways:
EX_GeographicBoundingBox - at least one of these should be present for resources that describe geographic resources
EX_GeographicDescription - One of these should be present for resources that describe geographic resources
EX_BoundingPolygon While very useful, particularly in describing irregular areas, this element is not described by the MDWG as a recommended element due to the difficult that many systems have in implementing it.
EX_TemporalExtent Contains temporal extent information for the cited resource

Outstanding Issues

verticalCRS The vertical CRS can be captured here or under the SpatialRefenceSystem package. We need to decide when to recommend capturing it here. As other extent parameters do not include the CRS, I would make a recommendation that we treat vertical the same and capture this info in the SRS section. Note BC 21-9: GN in the 19115-3 plugin captures the extent info as the old RS_Identifier instead of MD_Identifier

Units of measure These are not specified. I would suggest that we use metres relative to sea level WGS 84 as the universal units for vertical extents. As with the mandate of WGS 84 for the projection for bounding box extents, it is important to have as a close to a universally common reference frame as we can get to compare disparate resources.

Datum Issues What is “zero” is an open question. There may be little common between domains. In 3D cadastre, the level above ground may be the measure. There also is no agreement between land vertical datums and those for the sea.

Crosswalk considerations

Dublin core / CKAN / data.gov.au

Mapping to CKAN and Dublin core elements, particularly as used by data.gov.au needs discussion

DCAT

Maps to dct.spatial

RIF-CS

Maps to Coverage/Spatial

Examples

XML

<mdb:MD_Metadata>
....
  <mdb:identificationInfo>
   <mri:MD_DataIdentification>
     ....
     <mri:extent>
      <gex:EX_Extent>
        <gex:verticalElement>
         <gex:EX_VerticalExtent>
           <gex:minimumValue>
            <gco:Real>-1000</gco:Real>
           </gex:minimumValue>
           <gex:maximumValue>
            <gco:Real>1000</gco:Real>
           </gex:maximumValue>
           <gex:verticalCRSId>
            <mrs:MD_ReferenceSystem>
              <gmd:referenceSystemInfo xmlns:gmd="http://www.isotc211.org/2005/gmd">
               <gmd:MD_ReferenceSystem>
                 <gmd:referenceSystemIdentifier>
                  <gmd:RS_Identifier>
                    <gmd:code>
                     <gco:CharacterString 
                     xmlns:gco="http://www.isotc211.org/2005/gco">
                     WGS 84 (EPSG:4326)</gco:CharacterString>
                    </gmd:code>
                    <gmd:codeSpace>
                     <gco:CharacterString 
                     xmlns:gco="http://www.isotc211.org/2005/gco">
                     EPSG
                     </gco:CharacterString>
                    </gmd:codeSpace>
                    <gmd:version>
                     <gco:CharacterString 
                     xmlns:gco="http://www.isotc211.org/2005/gco">
                     8.6
                     </gco:CharacterString>
                    </gmd:version>
                  </gmd:RS_Identifier>
                 </gmd:referenceSystemIdentifier>
               </gmd:MD_ReferenceSystem>
              </gmd:referenceSystemInfo>
            </mrs:MD_ReferenceSystem>
           </gex:verticalCRSId>
         </gex:EX_VerticalExtent>
        </gex:verticalElement>
      </gex:EX_Extent>
     </mri:extent>
   ....
   </mri:MD_DataIdentification>
  </mdb:identificationInfo>
....
</mdb:MD_Metadata>

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UML diagrams

Recommended elements highlighted in yellow

ExVertical

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