Martin Desruisseaux created SIS-160:
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Summary: Need XSLT between GML 3.1 and 3.2
Key: SIS-160
URL: https://issues.apache.org/jira/browse/SIS-160
Project: Spatial Information Systems
Issue Type: Improvement
Components: Referencing
Affects Versions: 0.4
Reporter: Martin Desruisseaux
Priority: Minor
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 is 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 is more complex.
Example:
{code:xml|title=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>
{code}
{code:xml|title=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>
{code}
{{<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)|http://en.wikipedia.org/wiki/XSLT].
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 we can distribute under Apache 2
license. This work 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).
h3. 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).
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