[SIS-160] Need XSLT between GML 3.1 and 3.2

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 0.4, 0.5
• Component/s: Referencing
• Assignee: Unassigned
• Reporter: Martin Desruisseaux
• Created: 05/Jan/14 20:44
• Updated: 28/Jan/18 18:16

Description

Apache SIS supports natively only one GML version, typically the latest one (GML 3.2.1 as of Apache SIS 0.4). Reading a document from an older schema requires transforming the XML document before unmarshalling by SIS. Conversely, writing a document to an older schema requires transforming the XML document after marshalling by SIS.

Transformations between GML 3.2 and 3.2.1 are easy: only the name space URL changed. Such URL substitutions are done with our package-privated org.apache.sis.xml.FilteredStreamReader and FilteredStreamWriter classes. This is a lighter approach than using XSLT. However transformations between GML 3.1.1 and GML 3.2.1 are more complex. Example:

GML 3.1.1

<gml:VerticalDatum>
  <gml:datumName>Mean Sea Level</gml:datumName>
  <gml:remarks>Approximates geoid.</gml:remarks>
  <gml:anchorPoint>Averaged over a 19-year period.</gml:anchorPoint>
  <gml:validArea>
    <gml:description>World.</gml:description>
    <gml:boundingBox>
      <gml:lowerCorner>-180 -90</gml:lowerCorner>
      <gml:upperCorner>+180 +90</gml:upperCorner>
    </gml:boundingBox>
  </gml:validArea>
  <gml:scope>Hydrography.</gml:scope>
  <gml:verticalDatumType codeSpace="EPSG">geoidal</gml:verticalDatumType>
</gml:VerticalDatum>

GML 3.2.1

<gml:VerticalDatum>
  <gml:identifier codeSpace="OGP">urn:ogc:def:datum:EPSG::5100</gml:identifier>
  <gml:name>Mean Sea Level</gml:name>
  <gml:remarks>Approximates geoid.</gml:remarks>
  <gml:domainOfValidity>
    <gmd:EX_Extent>
      <gmd:description>
        <gco:CharacterString>World.</gco:CharacterString>
      </gmd:description>
      <gmd:geographicElement>
        <gmd:EX_GeographicBoundingBox>
          <gmd:westBoundLongitude><gco:Decimal>-180</gco:Decimal></gmd:westBoundLongitude>
          <gmd:eastBoundLongitude><gco:Decimal>+180</gco:Decimal></gmd:eastBoundLongitude>
          <gmd:southBoundLatitude><gco:Decimal> -90</gco:Decimal></gmd:southBoundLatitude>
          <gmd:northBoundLatitude><gco:Decimal> +90</gco:Decimal></gmd:northBoundLatitude>
        </gmd:EX_GeographicBoundingBox>
      </gmd:geographicElement>
    </gmd:EX_Extent>
  </gml:domainOfValidity>
  <gml:scope>Hydrography.</gml:scope>
  <gml:anchorDefinition>Averaged over a 19-year period.</gml:anchorDefinition>
</gml:VerticalDatum>

<gml:datumName> has been renamed as <gml:name>, <gml:anchorPoint> as <gml:anchorDefinition>, <gml:validArea> as <gml:domainOfValidity> with a very different content. <gml:identifier> does not exist in GML 3.1.1 but is mandatory in GML 3.2.1. Conversely, <gml:verticalDatumType> defined in GML 3.1.1 has been removed in GML 3.2.1. Those changes are too complex for our above-cited org.apache.sis.xml classes - we will need real XSLT (Extensible Stylesheet Language Transformations).

XSLT 1.0 is supported in JDK6. So the work needed for this task is to write the XSLT document, or to find existing XSLT that can be distributed under Apache 2 license. XSLT would works well as long as the Apache SIS native GML version contains all the information to write in the target GML versions. An exception to this condition is the above-cited <gml:verticalDatumType>, which have been removed from GML 3.2.1 and is uneasy to infer from other property values. This special case needs support straight in the org.apache.sis.referencing.datum.DefaultVerticalDatum class (already implemented in SIS 0.4).

Metadata

Transformations from ISO 19139:2003 to ISO 19115-3:2013 will be a similar challenge. But in this case, XSLT are made by ESRI. We need to check if the license is compatible, and to verify if we need to write ourselves the XSLT for the reverse transformation (newer to older).

Issue Links

• Is contained by: SIS-152 Consider using XSLT for handling XML documents compliant to different version of the standards
• is related to: SIS-192 Suppression of "3.2" in "http://www.opengis.net/gml/3.2" does not work
• is related to: SIS-381 Handle legacy ISO 19139:2007 format using XSL instead than private methods