Re: [thredds] ncml/THREDDS Aggregation of Swath Data follow up

  • To: Antonio S. Cofiño <cofinoa@xxxxxxxxx>
  • Subject: Re: [thredds] ncml/THREDDS Aggregation of Swath Data follow up
  • From: Michael McDonald <mcdonald@xxxxxxxxxxxxx>
  • Date: Mon, 11 May 2020 18:14:27 -0400
While the "along_track" is the UNLIMITED dimension in all of these
swath files. Our attempts to just use this as the dimension for the
joinExisting aggregation does not throw any issues wrt THREDDS at
catalog init time, but when you actually try to load/use this dataset
it does not work and fails with the message in Panoply,

"There was an error preparing the data: Failed creating the data
handler: Could not read lon axis array."

e.g., joinExisting aggregation on along_track (fails with: Could not
read lon axis array.)

 <netcdf xmlns="";>
    <aggregation type="joinExisting" dimName="along_track">
      <scan location="/Net/data/qscat/data/nc_L2B_v4p0_12/nc_L2B_12_daily/2009"
suffix=".nc" subdirs="false" />

This *simplified* product is a collection of multiple quikscat swath
passes in a 24 hour period to assemble a full coverage of the globe.


Which looks like this for a single day.

Our *end goal* is to have a virtually aggregated collection of all
this simplified daily swath data from 1999 to 2009 for ingestion as an
OPeNDAP/WMS dataset into a web-based data visualizer like OWGIS
(, so that users can pick the date(s) they want,
and view this in a web GUI.

We tried to use joinNew to aggregate all these like files on a new
dimension "T" and populate the time info using the filename
(dateFormatMark="QSCAT_#HH_yyyyDDD") and get the same error (fails
with: Could not read lon axis array.)

e.g., joinNew aggregation on new dimension T

<netcdf xmlns="";>
<aggregation dimName="T" type="joinNew">
<variableAgg name="time"/>
<variableAgg name="lon"/>
<variableAgg name="lat"/>
<variableAgg name="eastward_wind"/>
<variableAgg name="northward_wind"/>
<variableAgg name="wind_speed"/>
<variableAgg name="wind_to_direction"/>
<variableAgg name="simplified_wvc_quality_flag"/>
<variableAgg name="rain_impact"/>
<variableAgg name="distance_from_coast"/>
<scan dateFormatMark="QSCAT_#HH_yyyyDDD"
suffix=".nc" subdirs="false" />

Any ideas what we are doing wrong in THREDDS, or is the issue in the
data files we simplified?

> Ian,,
> What aggregation are you expecting? just on the 'along_track' dimension?
> Antonio
> On 5/5/20 19:46, Ian Dimitri wrote:
> Hello All,
> Adding onto Michael's existing thread, I am working closely with him 
> attempting to figure out the issue we are having with the aggregation of 
> swath data that has a two-dimensional grid with track and cross-track 
> coordinates. We have tried using FMRC, joinExisting, and joinNew file 
> aggregation methods within THREDDS, all with no success.
> We tried using many different aggregations methods
> that exist within the ncWMS2 interface. We have tried doing the simple 
> wildcard aggregation attempt by using the wildcard character (e.g. 
> /ASCAT/nc_L2B_25_daily/2020/*.nc).
> We have also tried to use the "Dynamic Services" that is also available 
> through ncWMS2, but that also did not seem to work with the multi-dimensional 
> swath data that we are
> trying to aggregate.
> Finally another method we tried was through geoserver, where we attempted to 
> use the image mosaic option that it has but that option also proved to be a 
> dead end.
> None of the methods mentioned above worked properly, and we are wondering if 
> anyone has had any success aggregating swath data with the methods, and would 
> like to share any
> special steps that had to be taken to make said method work. Are there any 
> other methods I did not mention above that could possibly be able to 
> aggregate the multi-demensional swath data?
> Any insight or help would be appreciated
> unaggregated data
> attempted aggregation with joinNew

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