Is there a hardwired limit to the NcML/THREDDS values element?

Question

Is there a limit to the size or number of entries that can be placed within the values NcML element? I'm attempting to get a set of NetCDF files without lon/lat variables - but with x/y variables - to be read as a featureCollection by adding NcML entries of the form:

<netcdf xmlns="http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2">
<variable name="lat_rho" shape="eta_rho xi_rho" type="float">
<attribute name="units" type="String" value="degrees_north" />
<values>[671x191 blankspace-separated latitudes here]</values>
</variable>

The lat and lon variables exist in a separate file and I've extracted them into single strings using ncks which I've stuck between appropriate locations.

The error messages in featureCollectionScan.log are:

[2013-02-07T15:15:37.386-0600] ERROR ucar.nc2.ft.fmrc.Fmrc: makeFmrcInv
java.lang.NullPointerException

....

[2013-02-07T15:15:37.388-0600] ERROR ucar.nc2.ft.fmrc.Fmrc:
/raid/data/txla_nesting6/.*\.nc$: makeFmrcInv failed
java.lang.RuntimeException: java.lang.NullPointerException

....

[2013-02-07T15:15:37.694-0600] WARN  ucar.nc2.ft.fmrc.GridDatasetInv: GridDatasetInv
using gds.getStartDate() for run date =%s
[2013-02-07T15:15:37.694-0600] ERROR ucar.nc2.ft.fmrc.Fmrc: makeFmrcInv
java.lang.NullPointerException

.... [2013-02-07T15:15:37.695-0600] ERROR ucar.nc2.ft.fmrc.Fmrc: /raid/data/txla_nesting6/.*.nc$: makeFmrcInv failed java.lang.RuntimeException: java.lang.NullPointerException

Answer 1

I don't know the answer to your question about the size limit for the <values> tag, but there is another way to solve your problem..

You can write your lon,lat values to a netcdf file, and then use a union aggregation to create a dataset that virtually joins that netcdf file to another netcdf file (or aggregation of netcdf files)

For example, if you have a bunch of files like:

mod_his_0001.nc
mod_his_0002.nc
...

that you want to aggregate along the time dimension and you create a netcdf file that contains the lon,lat variables:

lonlat.nc

you can aggregate them together like so:

<netcdf xmlns="http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2">
 <!-- union the (1) time aggregation with the (2) grid file -->
 <aggregation type="union">
  <!-- (1) time aggregate files like "mod_his_0001.nc" -->
  <netcdf xmlns="http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2">
   <aggregation dimName="time" type="joinExisting">
    <scan
     location="/home/baum/models/run01/"
     regExp=".*mod_his_[0-9]{4}\.nc$"/>
   </aggregation>
  </netcdf>
  <!-- (2) grid file -->
  <netcdf xmlns="http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2"
   location="/home/baum/models/lonlat.nc"/>
 </aggregation>
</netcdf>

Answer 2

Theres no limit to the number of values in the XML. You can test that by making an NcML file that just has that variable.

The problem you are seeing is likely in the FMRC, which is harder to debug here. Make sure you are using 4.3.