ISO Extents

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ISO 19115 combines spatial and temporal extents into a single object, called an EX_Extent, that includes temporal, vertical, and geographic extents. Dataset descriptions in ISO can include multiple extents.

The temporal and vertical extents are simple descriptions of temporal or vertical ranges.

The geographic extent can be described in three ways (see the abstract class section to understand the UML): The first option is a simple bounding box which works quite well in some simple situations. This is similar to the bounding box in the FGDC Metadata Standard, except that the FGDC box described the spatial extent of the entire dataset and this Extent object gives the spatial extent of a specific quality report.

The second option generalizes the bounding box to a bounding polygon. This covers a large number of cases which might involve natural shapes, such as watersheds, or political shapes, like county forecast zones, rather than rectangles. In the FGDC Standard this is similar to the G-Ring option for the spatial extent, except that it applies only to a specific quality report.

The final option allows specification of an identifier of a geographic region. This identifier includes a namespace and a name and allows the use of named spatial objects, like counties, to describe spatial extents. This is similar to the spatial keyword element of the FGDC Metadata Standard.

The EX_Extent object allows multiple geographic and temporal extents in a single object which can be very helpful for datasets collected in different locations at different times. For example, a dataset might include observations made at different locations each field season. The EX_SpatialTemporalExtent object is a container within the EX_Extent that can be used to group the appropriate locations and times together.

Applications

ISO extents can be used in four locations:

  1. MD_Identification extents describe any number of extents for a dataset or a service (in the INSPIRE Metadata Guidelines0.
  2. DQ_DataQuality/scope/DQ_Scope allows a single extent to be associated with a data quality lineage or report.
  3. DQ_DataQuality/lineage/LI_Lineage/source describes the spatial and temporal extent of a source used in a dataset.
  4. RS_ReferenceSystem describes the extent of validity of a given ReferenceSystem.

The revision of 19115 adds extents to:

  1. CI_ResponsibleParty to describe spatial/temporal extents of responsibilities.
  2. MD_Constraints to describe spatial/temporal extents of constraints.

Examples

Ex_Extent

extent:  (EX_Extent)
 geographicElement:  (EX_GeographicBoundingBox)
   westBoundLongitude:  -171.76409
   eastBoundLongitude:  -157.86768
   southBoundLatitude:  -14.42443
   northBoundLatitude:  21.31573
 temporalElement:  (EX_TemporalExtent)
  extent:
   TimePeriod:
    beginPosition:  2010-05-17
    endPosition:  2010-06-16
extent:  (EX_Extent)
 description:  KingmanPalmyra_line_100
 geographicElement:  (EX_GeographicBoundingBox)
   westBoundLongitude:  -162.14217
   eastBoundLongitude:  -161.55155
   southBoundLatitude:  4.94414
   northBoundLatitude:  5.28984
 temporalElement:  (EX_TemporalExtent)
  extent:
   TimePeriod:
    beginPosition:  2010-06-05T12:00:17
    endPosition:  2010-06-05T15:15:37

Bounding Extent

This example describes a simple spatial and temporal extent for a dataset that extends to the present. It includes ids (boundingExtent, boundingBox, and boundingTime) that allow the bounding extents to be referenced from other parts of the record or from external sources. These can also be used when translating the ISO metadata to standards that include only a bounding extent. It also include a geographicIdentifier, in this case a location keyword from the NASA GCMD.

<gmd:extent>
    <gmd:EX_Extent id="boundingExtent">
        <gmd:geographicElement>
            <gmd:EX_GeographicBoundingBox id="boundingGeographicBoundingBox">
                <gmd:extentTypeCode>
                    <gco:Boolean>true</gco:Boolean>
                </gmd:extentTypeCode>
                <gmd:westBoundLongitude>
                    <gco:Decimal>-178</gco:Decimal>
                </gmd:westBoundLongitude>
                <gmd:eastBoundLongitude>
                    <gco:Decimal>180</gco:Decimal>                    
                </gmd:eastBoundLongitude>
                <gmd:southBoundLatitude>
                    <gco:Decimal>-78</gco:Decimal>
                </gmd:southBoundLatitude>
                <gmd:northBoundLatitude>
                    <gco:Decimal>75</gco:Decimal>
                </gmd:northBoundLatitude>
            </gmd:EX_GeographicBoundingBox>           
        </gmd:geographicElement>
        <gmd:geographicElement>
            <gmd:EX_GeographicDescription>
                <gmd:geographicIdentifier>
                    <gmd:MD_Identifier>
                        <gmd:authority>
                            <gmd:CI_Citation>
                                <gmd:title>
                                    <gco:CharacterString>NASA/GCMD Location Keywords</gco:CharacterString>
                                </gmd:title>
                                <gmd:date>
                                    <gmd:CI_Date>
                                        <gmd:date>
                                            <gco:Date>2009-01-01</gco:Date>
                                        </gmd:date>
                                        <gmd:dateType>
                                            <gmd:CI_DateTypeCode codeList="http://www.isotc211.org/2005/resources/Codelist/gmxCodelists.xml#CI_DateTypeCode" codeListValue="revision">revision</gmd:CI_DateTypeCode>
                                        </gmd:dateType>
                                    </gmd:CI_Date>
                                </gmd:date>
                            </gmd:CI_Citation>
                        </gmd:authority>
                        <gmd:code>
                            <gco:CharacterString>Location > Geographic Region > Global Ocean</gco:CharacterString>
                        </gmd:code>
                    </gmd:MD_Identifier>
                </gmd:geographicIdentifier>
            </gmd:EX_GeographicDescription>
        </gmd:geographicElement>
        <gmd:temporalElement>
            <gmd:EX_TemporalExtent id="boundingTemporalExtent">
                <gmd:extent>
                    <gml:TimePeriod gml:id="someTimeID">
                        <gml:beginPosition>1846</gml:beginPosition>
                        <gml:endPosition indeterminatePosition="now"/>
                    </gml:TimePeriod>                    
                </gmd:extent>
            </gmd:EX_TemporalExtent>
        </gmd:temporalElement>
        <gmd:verticalElement>
            <gmd:EX_VerticalExtent>
              <gmd:minimumValue>
                <gco:Real>10</gco:Real>
              </gmd:minimumValue>
              <gmd:maximumValue>
                <gco:Real>2810</gco:Real>
              </gmd:maximumValue>
              <gmd:verticalCRS gco:nilReason="unknown"/>
            </gmd:EX_VerticalExtent>
          </gmd:verticalElement>
        </gmd:EX_Extent>
    </gmd:EX_Extent>
</gmd:extent>
</pre>

=== Vertical Extent ===
* This example uses a coordinate reference system described at the [http://www.epsg-registry.org/ EPSG Registry]
<pre>
<gmd:verticalElement>
 <gmd:EX_VerticalExtent>
  <gmd:minimumValue>
   <gco:Real> 3600 </gco:Real>
  </gmd:minimumValue>
  <gmd:maximumValue>
   <gco:Real> 3100 </gco:Real>
  </gmd:maximumValue>
  <gmd:verticalCRS xlink:href="http://www.epsg-registry.org/export.htm?gml=urn:ogc:def:crs:EPSG::5715" xlink:title="msl depth in meters" xlink:actuate="onRequest"/>
 </gmd:EX_VerticalExtent>
</gmd:verticalElement>

Detailed Extents

Bounding extents work well for describing datasets that are close to rectangular in their distributions. They work poorly for datasets that are disjoint. In those cases, multiple extents can be used to provide a more accurate description of the spatial/temporal distribution of a dataset. These extents are termed detailed extents. They can be described in several ways.

Multiple extents with descriptions

The critical characteristic of the examples shown above is that they use a single bounding gmd:extent object with multiple that includes multiple extent descriptions. The ISO Standard allows multiple extent objects in gmd:MD_DataIdentification/extent, LI_Source/sourceExtent, and RS_ReferenceSystem/domainOfValidity roles. In those cases it may be more straightforward to repeat entire gmd:extent objects. This approach allows the gmd:description object, a CharacterString, to be used to label the extents. This is more flexible than the other approaches that use the somewhat limited xml id for this purpose.

<gmd:extent>
  <gmd:EX_Extent>
    <gmd:description>
      <gco:CharacterString>PORTS Network in Gulfport</gco:CharacterString>
    </gmd:description>
    <gmd:geographicElement>
      <gmd:EX_GeographicBoundingBox>
        <gmd:extentTypeCode>
          <gco:Boolean>1</gco:Boolean>
        </gmd:extentTypeCode>
        <gmd:westBoundLongitude>
          <gco:Decimal>-89.0869</gco:Decimal>
        </gmd:westBoundLongitude>
        <gmd:eastBoundLongitude>
          <gco:Decimal>-88.9788</gco:Decimal>
        </gmd:eastBoundLongitude>
        <gmd:southBoundLatitude>
          <gco:Decimal>30.1986</gco:Decimal>
        </gmd:southBoundLatitude>
        <gmd:northBoundLatitude>
          <gco:Decimal>30.3478</gco:Decimal>
        </gmd:northBoundLatitude>
      </gmd:EX_GeographicBoundingBox>
    </gmd:geographicElement>
  </gmd:EX_Extent>
</gmd:extent>
<gmd:extent>
  <gmd:EX_Extent>
    <gmd:description>
      <gco:CharacterString>PORTS Network in Lake Charles</gco:CharacterString>
    </gmd:description>
    <gmd:geographicElement>
      <gmd:EX_GeographicBoundingBox>
        <gmd:extentTypeCode>
          <gco:Boolean>1</gco:Boolean>
        </gmd:extentTypeCode>
        <gmd:westBoundLongitude>
          <gco:Decimal>-93.3432</gco:Decimal>
        </gmd:westBoundLongitude>
        <gmd:eastBoundLongitude>
          <gco:Decimal>-93.2216</gco:Decimal>
        </gmd:eastBoundLongitude>
        <gmd:southBoundLatitude>
          <gco:Decimal>29.6946</gco:Decimal>
        </gmd:southBoundLatitude>
        <gmd:northBoundLatitude>
          <gco:Decimal>30.2236</gco:Decimal>
        </gmd:northBoundLatitude>
      </gmd:EX_GeographicBoundingBox>
    </gmd:geographicElement>
  </gmd:EX_Extent>
</gmd:extent>

Extents for Lines

<gmd:extent>
 <gmd:EX_Extent>
  <gmd:description>
   <gco:CharacterString>coordinates of ship track</gco:CharacterString>
  </gmd:description>
  <gmd:geographicElement>
   <gmd:EX_BoundingPolygon>
    <gmd:polygon>
     <gml:LineString gml:id="coordsId1" srsName="urn:ogc:def:crs:EPSG::4326">
      <gml:posList>
120.27748,22.61839 120.18761,22.63769 120.17214,22.53991 120.05429,22.16867 120.01199,22.12645 120.00135,22.01943 120.06252,21.90396 120.35294,21.48403 120.37861,21.40571 120.37604,21.34815 120.35906,21.30502 120.10236,21.19057 120.08512,21.16013 120.10072,21.13824 120.22287,21.18813 120.33551,21.2616 120.4239,21.33915 120.42161,21.38913 119.55256,22.76568 119.52194,22.78651 119.49204,22.77439 119.47786,22.7447 119.52109,22.60486 119.6674,22.47499 119.73458,22.36784 119.78415,22.37223 119.78778,22.39893 119.4742,22.88693 119.44816,22.89744 119.37347,22.88857 119.2269,22.71746 119.22485,22.69423 119.94128,21.34452 119.9266,21.32749 118.94901,20.98167 118.92662,20.94138 118.94507,20.87394 118.96713,20.86117 119.01475,20.89636 119.02009,20.91664 118.63907,22.46099 118.61382,22.47876 118.43864,22.43546 118.43536,22.4088 118.71316,21.91484 118.70609,21.89098 118.67994,21.88721 118.56096,21.95114 118.55874,21.98347 118.64336,21.99787 118.66055,21.98785 118.64147,21.82774 118.61678,21.81229 118.47464,21.83414 118.48164,21.97625 118.84612,22.01791 118.86534,22.03534 118.84197,22.05854 118.6668,22.05099 118.66114,22.02321 118.71922,22.00649 118.91635,22.02485 120.20044,22.33125 120.22671,22.32764 120.23685,22.30713 120.12194,22.24198 120.02058,22.20767 120.01453,22.33463 120.07933,22.40964 120.11473,22.41882 120.12845,22.39332 119.03449,21.22713 117.7411,19.81533 116.68832,18.64108 116.69465,18.59847 116.71919,18.60374 117.05876,18.99421 117.11727,19.0143 120.52804,19.0021 120.61806,18.99966 120.63304,18.9875 120.62917,18.96598 120.41416,18.76345 120.38721,18.7607 119.02394,19.77431 119.02822,19.82094 119.06,19.84202 119.68217,19.83289 119.71366,19.80128 119.6868,19.78108 119.6465,19.81361 119.19845,22.65374 119.165,22.67165 119.01307,22.59032 119.0026,22.57115 119.06168,22.30221 119.05849,22.25761 119.24312,21.19685 119.2492,21.11487 119.20852,21.0894 119.19279,21.10616 119.11855,21.39059 119.13674,21.41605 122.37164,21.43583 122.50458,21.43177 122.6536,21.37249 122.63804,21.36041 122.49444,21.35543 122.4702,21.35882 122.46093,21.37889 122.46155,21.41366 122.48147,21.43206 123.96004,21.41706 123.98266,21.38761 123.49006,20.56702 121.74597,20.58839 119.01211,20.57019 119.00054,20.58882 119.0115,20.68749 121.06908,21.78377 122.20265,21.78282 122.23269,21.75552 122.24475,21.58202 122.21953,21.56438 122.16919,21.56932 122.16693,22.02628 122.12405,22.05799 121.53854,21.82368 121.2374,21.82707 120.94554,21.66996 120.75636,21.66697 120.61447,21.81164 120.60776,21.85963 120.56905,21.90118 120.34866,21.9903 119.15291,22.65674 119.16538,22.69908 119.30981,22.71573 119.31802,22.73753 119.30344,22.75893 119.27629,22.76466 119.15187,22.71012 119.17847,22.71574 119.18939,22.738 119.17478,22.69522 119.21214,22.73434 119.5153,22.70518 119.52339,22.74833 119.50918,22.7724 119.5115,22.71706 119.52945,22.70059 119.74558,22.67439 119.827,22.68315 120.05737,22.62181 120.28458,22.61497
      </gml:posList>
      </gml:LineString>
     </gmd:polygon>
    </gmd:EX_BoundingPolygon>
   </gmd:geographicElement>
  </gmd:EX_Extent>
</gmd:extent>