Special and Temporal Extents

From Earth Science Information Partners (ESIP)

The Extent Spiral defines the spatial and temporal extent of the dataset. This information can be displayed on maps, profiles and timelines and used in spatial and temporal searches. Most documentation dialects include this information because it is so important to data discovery.

ISO Dialects

The ISO standard supports the definition of multiple extents for each dataset/service. In order to simplify the process of identifying the bounding extent, it is recommended that the id attribute be set = "boundingExtent" (see ISO Extents).

NASA GCMD Directory Interchange Format

The DIF format assumes that place keywords come from the GCMD Location Keywords.

netCDF

Extent information is included in the Attribute Conventions for Data Discovery and ctCDF files as global attributes:

<attribute name="geospatial_lat_max" value="90.0 " type="double"/>
<attribute name="geospatial_lat_min" value="-90.0 " type="double"/>
<attribute name="geospatial_lat_resolution" value="0.0416 " type="double"/>
<attribute name="geospatial_lat_units" value="degrees_north"/>
<attribute name="geospatial_lon_max" value="360.0 " type="double"/>
<attribute name="geospatial_lon_min" value="0.0 " type="double"/>
<attribute name="geospatial_lon_resolution" value="0.0416 " type="double"/>
<attribute name="geospatial_lon_units" value="degrees_east"/>
<attribute name="geospatial_vertical_max" value="0.0 " type="double"/>
<attribute name="geospatial_vertical_min" value="0.0 " type="double"/>
<attribute name="geospatial_vertical_positive" value="up"/>
<attribute name="geospatial_vertical_units" value="m"/>

Many of the attributes included in this spiral can be calculated from the data using standard netCDF Tools if the file is compliant with the NetCDF Climate and Forecast (CF) Metadata Convention. In ncISO these attributes are given as part of the CFMetadata group:

<group name="CFMetadata">
    <attribute name="geospatial_lon_min" value="-180.0" type="float" />
    <attribute name="geospatial_lat_min" value="-80.0" type="float" />
    <attribute name="geospatial_lon_max" value="179.5" type="float" />
    <attribute name="geospatial_lat_max" value="85.0" type="float" />
    <attribute name="geospatial_lon_units" value="degrees_east" />
    <attribute name="geospatial_lat_units" value="degrees_north" />
    <attribute name="geospatial_lon_resolution" value="0.5" />
    <attribute name="geospatial_lat_resolution" value="0.5" />
    <attribute name="time_coverage_start" value="2010-05-29T22:00:00Z" />
    <attribute name="time_coverage_end" value="2011-05-21T20:00:00Z" />
    <attribute name="time_coverage_units" value="seconds" />
    <attribute name="time_coverage_resolution" value="314669.0" />
    <attribute name="time_coverage_duration" value="P0Y0M356DT22H0M0.000S" />
  </group>

THREDDS

The THREDDS dialect defines spatial ranges using start, size, resolution, and units and includes place keywords with vocabulary names.

<geospatialCoverage zpositive="down">
    <northsouth>
        <start>10</start>
        <size>80</size>
        <resolution>2</resolution>
        <units>degrees_north</units>
    </northsouth>
    <eastwest>
        <start>-130</start>
        <size>260</size>
        <resolution>2</resolution>
        <units>degrees_east</units>
    </eastwest>
    <updown>
        <start>0</start>
        <size>22</size>
        <resolution>0.5</resolution>
        <units>km</units>
    </updown>
    <name vocabulary="GCMD Location Keywords">Arctic Ocean</name>
</geospatialCoverage>

Crosswalks

Concept Description Paths
Southernmost Latitude The southernmost latitude of the bounding rectangle.

Note: OGC-SOS offering lists may not include the entire dataset. A gml:id attribute can be used to identify the bounding offering.
OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/gml:boundedBy/gml:Envelope/gml:lowerCorner
ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:geographicElement/gmd:EX_GeographicBoundingBox/gmd:southBoundLatitude/gco:Decimal
THREDDS /thredds:catalog/thredds:metadata/thredds:geospatialCoverage/thredds:northsouth/thredds:start
THREDDS /thredds:catalog/thredds:dataset/thredds:geospatialCoverage/thredds:northsouth/thredds:start
netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=geospatial_lat_min]
Northernmost Latitude The northernmost latitude of the bounding rectangle.

Note: OGC-SOS offering lists may not include the entire dataset. A gml:id attribute (e.g. gml:id="network-all") can be used to identify the bounding offering.
OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/gml:boundedBy/gml:Envelope/gml:upperCorner
ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:geographicElement/gmd:EX_GeographicBoundingBox/gmd:northBoundLatitude/gco:Decimal
netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=geospatial_lat_max]
Westernmost Longitude The westernmost longitude of the bounding rectangle.

Note: OGC-SOS offering lists may not include the entire dataset. A gml:id attribute can be used to identify the bounding offering.
OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/gml:boundedBy/gml:Envelope/gml:lowerCorner
ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:geographicElement/gmd:EX_GeographicBoundingBox/gmd:westBoundLongitude/gco:Decimal
THREDDS /thredds:catalog/thredds:metadata/thredds:geospatialCoverage/thredds:eastwest/thredds:start
THREDDS /thredds:catalog/thredds:dataset/thredds:geospatialCoverage/thredds:eastwest/thredds:start
netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=geospatial_lon_min]
Easternmost Longitude The westernmost longitude of the bounding rectangle.

Note: OGC-SOS offering lists may not include the entire dataset. A gml:id attribute can be used to identify the bounding offering.
OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/gml:boundedBy/gml:Envelope/gml:upperCorner
ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:geographicElement/gmd:EX_GeographicBoundingBox/gmd:eastBoundLongitude/gco:Decimal
netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=geospatial_lon_max]
Start Time The start of the bounding time period OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/sos:time/gml:TimePeriod/gml:beginPosition
ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:temporalElement/gmd:EX_TemporalExtent/gmd:extent/gml:TimePeriod/gml:beginPosition
THREDDS /thredds:catalog/thredds:dataset/thredds:timeCoverage/thredds:start
THREDDS /thredds:catalog/thredds:metadata/thredds:timeCoverage/thredds:start
netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=time_coverage_start]
End Time The end of the bounding time period OGC-SOS /sos:Capabilities/sos:Contents/sos:ObservationOfferingList/sos:ObservationOffering/sos:time/gml:TimePeriod/gml:endPosition
ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:temporalElement/gmd:EX_TemporalExtent/gmd:extent/gml:TimePeriod/gml:endPosition
THREDDS /thredds:catalog/thredds:dataset/thredds:timeCoverage/thredds:end
THREDDS /thredds:catalog/thredds:metadata/thredds:timeCoverage/thredds:end
netCDF /nc:netcdf/nc:CFMetadata/nc:attribute[@name=time_coverage_end]
Vertical Minimum The minimum height of the bounding rectangle ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:verticalElement/gmd:EX_VerticalExtent/gmd:minimumValue/gco:Real
THREDDS /thredds:catalog/thredds:metadata/thredds:geospatialCoverage/thredds:updown/thredds:start
THREDDS /thredds:catalog/thredds:dataset/thredds:geospatialCoverage/thredds:updown/thredds:start
netCDF /nc:netcdf/nc:attribute[@name=geospatial_vertical_min]
Vertical Maximum The maximum height of the bounding rectangle ISO /*/gmd:identificationInfo/*/gmd:extent/gmd:EX_Extent/gmd:verticalElement/gmd:EX_VerticalExtent/gmd:maximumValue/gco:Real
netCDF /nc:netcdf/nc:attribute[@name=geospatial_vertical_max]
Place Keyword A comma separated list of key words and phrases that give the location of the resource.

Note: Some dialects include keywords, but they do not include mechanisms for identifying the type. In those cases it is difficult to unambiguously identify place keywords.
ISO /*/gmd:identificationInfo/*/gmd:descriptiveKeywords/gmd:MD_Keywords[gmd:type/gmd:MD_KeywordTypeCode='place']/gmd:keyword/gco:CharacterString
THREDDS /thredds:catalog/thredds:dataset/thredds:geospatialCoverage/thredds:name
Place Keyword Vocabulary If you are following a guideline for the place words/phrases in your "keywords" attribute, put the name of that guideline here. ISO /*/gmd:identificationInfo/*/gmd:descriptiveKeywords/gmd:MD_Keywords[gmd:type/gmd:MD_KeywordTypeCode='place']/gmd:thesaurusName/gmd:CI_Citation/gmd:title/gco:CharacterString
THREDDS /thredds:catalog/thredds:dataset/thredds:geospatialCoverage/thredds:name/@thredds:vocabulary

xPath Note: The xPaths included in this table use several wildcards. // means any path, so //gmd:CI_ResponsibleParty indicates a gmd:CI_ResponsibleParty anywhere in an XML file. /*/ indicates a single level with several possible elements. This usually indicates one of several concrete realizations of an abstract object. For example /*/gmd:identificationInfo could be gmd:MD_Metadata/gmd:identificationInfo or gmi:MI_Metadata/gmd:identificationInfo and gmd:identificationInfo//*/gmd:descriptiveKeywords could be gmd:identificationInfo/gmd:MD_DataIdentification/gmd:descriptiveKeywords or gmd:identificationInfo/srv:SV_ServiceIdentification/gmd:descriptiveKeywords.

Page - Section 3 - Metadata Implementation