Hello all
We finished the GML (Geographic Markup Language) support for Conversion
and Transformation objects. GML support for ConcatenatedOperation and
PassThroughOperation objects are deferred to a next release. An example
of <gml:Transformation> element can be view at [1]. This example is only
performing a subtraction in the longitude value.
There is numerous other projects capable to read and write GML
documents. Many projects took the XSD files published by OGC at [2] and
generated automatically the Java classes using JAXB compiler for
instance. Differences between such projects and Apache SIS are:
1. SIS hides many GML complexity (e.g. automatic tools applied on GML
tend to generate twice the amount of classes than what exist in the
conceptual model).
2. SIS objects are ready for use immediately after unmarshalling. They
are not just containers where information has been copied verbatim
from the XML document. The information has been extensively analysed
and processed, so the SIS object is ready for executing map projections.
Note that point 2 can also be an inconvenient: if SIS has been unable to
process the information (e.g. if it does not recognize a map projection
parameter), an exception may be raised. This behaviour may not be
appropriate if a user just wants to browse the document in a tree
without performing computation. For such cases, we may suggest to use
DOM instead.
This GML support is new - it did not existed in Geotk (or at least not
in the form of "intelligent" objects). Consequently there is a risk that
we discover some issues after the releases. Nevertheless I wanted to do
this work before the release because GML was known to be broken in some
SIS classes. The intend is to provide a "all or nothing" behaviour: if a
class support GML, at least make that GML valid as much as we can.
Tomorrow I will complete support of <gml:ProjectedCRS> (the last
"broken" class), then I think we will be done for GML in the proposed
Apache SIS 0.6 release.
Martin
[1]
http://svn.apache.org/repos/asf/sis/branches/JDK8/core/sis-referencing/src/test/resources/org/apache/sis/referencing/operation/Transformation.xml
[2] http://schemas.opengis.net/gml/3.2.1/
