/**
* Opens the NetCDF dataset at the given location, using the dataset cache if {@code location}
* represents an NcML aggregation. We cannot use the cache for OPeNDAP or single NetCDF files
* because the underlying data may have changed and the NetcdfDataset cache may cache a dataset
* forever. In the case of NcML we rely on the fact that server administrators ought to have set a
* "recheckEvery" parameter for NcML aggregations that may change with time. It is desirable to
* use the dataset cache for NcML aggregations because they can be time-consuming to assemble and
* we don't want to do this every time a map is drawn.
*
* @param location The location of the data: a local NetCDF file, an NcML aggregation file or an
* OPeNDAP location, {@literal i.e.} anything that can be passed to
* NetcdfDataset.openDataset(location).
* @return a {@link NetcdfDataset} object for accessing the data at the given location.
* @throws IOException if there was an error reading from the data source.
*/
private NetcdfDataset openAndAggregateDataset(String location) throws IOException, EdalException {
NetcdfDataset nc;
if (location.startsWith("dods://") || location.startsWith("http://")) {
/*
* We have a remote dataset
*/
nc = CdmUtils.openDataset(location);
} else {
/*
* We have a local dataset
*/
List<File> files = null;
try {
files = CdmUtils.expandGlobExpression(location);
} catch (NullPointerException e) {
System.out.println("NPE processing location: " + location);
throw e;
}
if (files.size() == 0) {
throw new EdalException(
"The location " + location + " doesn't refer to any existing files.");
}
if (files.size() == 1) {
location = files.get(0).getAbsolutePath();
nc = CdmUtils.openDataset(location);
} else {
/*
* We have multiple files in a glob expression. We write some
* NcML and use the NetCDF aggregation libs to parse this into
* an aggregated dataset.
*
* If we have already generated the ncML on a previous call,
* just use that.
*/
if (ncmlString == null) {
/*
* Find the name of the time dimension
*/
NetcdfDataset first = openAndAggregateDataset(files.get(0).getAbsolutePath());
String timeDimName = null;
for (Variable var : first.getVariables()) {
if (var.isCoordinateVariable()) {
for (Attribute attr : var.getAttributes()) {
if (attr.getFullName().equalsIgnoreCase("units")
&& attr.getStringValue().contains(" since ")) {
/*
* This is the time dimension. Since this is
* a co-ordinate variable, there is only 1
* dimension
*/
Dimension timeDimension = var.getDimension(0);
timeDimName = timeDimension.getFullName();
}
}
}
}
first.close();
if (timeDimName == null) {
throw new EdalException("Cannot join multiple files without time dimensions");
}
/*
* We can't assume that the glob expression will have
* returned the files in time order.
*
* We could assume that alphabetical == time ordered (and
* for properly named files it will - but let's not rely on
* our users having sensible naming conventions...
*
* Sort the list using a comparator which opens the file and
* gets the first value of the time dimension
*/
final String aggDimName = timeDimName;
Collections.sort(
files,
new Comparator<File>() {
@Override
public int compare(File ncFile1, File ncFile2) {
NetcdfFile nc1 = null;
NetcdfFile nc2 = null;
try {
nc1 = NetcdfFile.open(ncFile1.getAbsolutePath());
nc2 = NetcdfFile.open(ncFile2.getAbsolutePath());
Variable timeVar1 = nc1.findVariable(aggDimName);
Variable timeVar2 = nc2.findVariable(aggDimName);
long time1 = timeVar1.read().getLong(0);
long time2 = timeVar2.read().getLong(0);
return Long.compare(time1, time2);
} catch (Exception e) {
/*
* There was a problem reading the data. Sort
* alphanumerically by filename and hope for the
* best...
*
* This catches all exceptions because however
* it fails this is still our best option.
*
* If the error is a genuine problem, it'll show
* up as soon as we try and aggregate.
*/
return ncFile1.getAbsolutePath().compareTo(ncFile2.getAbsolutePath());
} finally {
if (nc1 != null) {
try {
nc1.close();
} catch (IOException e) {
log.error("Problem closing netcdf file", e);
}
}
if (nc2 != null) {
try {
nc2.close();
} catch (IOException e) {
log.error("Problem closing netcdf file", e);
}
}
}
}
});
/*
* Now create the NcML string and use it to create an
* aggregated dataset
*/
StringBuffer ncmlStringBuffer = new StringBuffer();
ncmlStringBuffer.append(
"<netcdf xmlns=\"http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2\">");
ncmlStringBuffer.append(
"<aggregation dimName=\"" + timeDimName + "\" type=\"joinExisting\">");
for (File file : files) {
ncmlStringBuffer.append("<netcdf location=\"" + file.getAbsolutePath() + "\"/>");
}
ncmlStringBuffer.append("</aggregation>");
ncmlStringBuffer.append("</netcdf>");
ncmlString = ncmlStringBuffer.toString();
}
nc = NcMLReader.readNcML(new StringReader(ncmlString), null);
}
}
return nc;
}
