Hi Christian:
Actually I prefer to answer questions on this email group, as it allows others
to comment also. The support-netcdf-java (aka esupport) is better to make sure
questions dont get lost, however.
some responses below
Christian Ward-Garrison wrote:
Hi John,
The following is valid NcML according to ncml-2.2.xsd, but causes an
exception in toolsUI
<netcdf xmlns="http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2";>
<aggregation dimName="outer" type="joinNew">
<netcdf>
<dimension name="inner" length="4" />
<variable name="inner" shape="inner" type="int">
<values>1 2 3 4</values>
</variable>
</netcdf>
</aggregation>
</netcdf>
java.lang.NullPointerException
at
ucar.nc2.ncml.AggregationOuterDimension$DatasetOuterDimension.<init>(AggregationOuterDimension.java:609)
at
ucar.nc2.ncml.AggregationOuterDimension.makeDataset(AggregationOuterDimension.java:555)
at ucar.nc2.ncml.Aggregation.addExplicitDataset(Aggregation.java:194)
at ucar.nc2.ncml.NcMLReader.readAgg(NcMLReader.java:1313)
at ucar.nc2.ncml.NcMLReader.readNetcdf(NcMLReader.java:466)
at ucar.nc2.ncml.NcMLReader.readNcML(NcMLReader.java:414)
at ucar.nc2.ncml.NcMLReader.readNcML(NcMLReader.java:235)
at ucar.nc2.ncml.NcMLReader.readNcML(NcMLReader.java:185)
at ucar.nc2.dataset.NetcdfDataset.acquireNcml(NetcdfDataset.java:797)
at
ucar.nc2.dataset.NetcdfDataset.openOrAcquireFile(NetcdfDataset.java:673)
at ucar.nc2.dataset.NetcdfDataset.openFile(NetcdfDataset.java:567)
at ucar.nc2.ui.ToolsUI$NCdumpPanel.run(ToolsUI.java:1378)
at ucar.nc2.ui.ToolsUI$GetDataTask.run(ToolsUI.java:4264)
at java.lang.Thread.run(Unknown Source)
NJ is trying to come up with coordinate values for the new dimension.
There is no "coordValue" attribute for the nested dataset, so it looks
for a "location" attribute, which also doesn't exist. Unfortunately, NJ
doesn't anticipate this possibility, and a NullPointerException gets
thrown as a result.
The resolution for this problem is to add a "coordValue" attribute, but
the schema doesn't enforce that and the exception doesn't suggest that.
Maybe it's not possible to modify the schema such that it requires a
"coordValue" or "location" attribute for each dataset in a joinNew
aggregation (I don't know a ton about what's possible with XSD), but it
at least seems worthwhile to throw an exception with a more useful error
message.
Yes, XML Schema is inadequate for complex constraints like that. For various
reasons its difficult to get good error detection in parsing NcML, but ill try
your example and see if I can improve it.
As you note, JoinNew aggregation requires a coordinate variable. One needs to
read the docs at
http://www.unidata.ucar.edu/software/netcdf/ncml/v2.2/Aggregation.html
to learn about these subtleties. It appears however, that the doc is not all
that clear on this point of needing a coordinate variable. Ill try to improve
that also.
