Example

Here’s an example of a very simple catalog:

<?xml version="1.0" ?>  <!-- 1 -->
<catalog xmlns="http://www.unidata.ucar.edu/namespaces/thredds/InvCatalog/v1.0" > <!-- 2 -->
  <service name="odap" serviceType="OpenDAP" base="/thredds/dodsC/" /> <!-- 3 -->
  <dataset name="SAGE III Ozone 2006-10-31" serviceName="odap" urlPath="sage/20061031.nc" ID="20061031.nc"/> <!-- 4 -->
</catalog> <!-- 5 -->

with this line-by-line explanation:

  1. The first line indicates that this is an XML document.
  2. This is the root element of the XML, the catalog element. It must declare the THREDDS catalog namespace with the xmlns attribute exactly as shown.
  3. This declares a service named odap that will serve data via the OpenDAP protocol. Many other data access services come bundled with THREDDS.
  4. This declares a dataset named SAGE III Ozone 2006-10-31. It references the odap service on line 3, meaning it will be served via OpenDAP. The URLPath of sage/20061031.nc will provided a needed compontent to build the access URL
  5. This closes the catalog element.

Using the catalog directly above, here are the steps for client software to construct a dataset access URL:

  1. Find the service referenced by the dataset:

    <service name="odap" serviceType="OpenDAP" base="/thredds/dodsC/" />
<dataset name="SAGE III Ozone 2006-10-31" serviceName="odap" urlPath="sage/20061031.nc" ID="20061031.nc"/>
  2. Append the service base path to the server root to construct the service base URL:
    • serverRoot = http://hostname:port
    • serviceBasePath = /thredds/dodsC/
    • serviceBaseUrl = serverRoot + serviceBasePath = http://hostname:port/thredds/dodsC/`
  3. Find the urlPath referenced by the dataset: 
    <dataset name="SAGE III Ozone 2006-10-31" serviceName="odap" urlPath="sage/20061031.nc" ID="20061031.nc"/>
  4. Append the dataset urlPath to the service base URL to get the dataset access URL:
    • serviceBaseUrl = http://hostname:port/thredds/dodsC/
    • datasetUrlPath = sage/20061031.nc
    • datasetAccessUrl = serviceBaseUrl + datasetUrlPath = http://hostname:port/thredds/dodsC/sage/20061031.nc

In summary, construct a URL from a client catalog with these 3 pieces:

http://hostname:port/thredds/dodsC/sage/20061031.nc
<------------------><------------><--------------->
     server            service         dataset