Discovery
---------

The catalog is a web service that returns metadata of Earth Observation products in various formats when queried.

This section is about **discovery**, i.e. the question what the catalog actually offers. The ways how to use the catalog for queries are covered in the next :ref:`the next section <search>`. 

Terradue's catalog is at the URL https://catalog.terradue.com

The catalog is divided into compartments of metadata, called **indices**. These are used to separate information based on the purposes for which it is used, and for access control.
You have access to your own personal index and to a number of others, based on your affiliation and roles in projects.



Exploring indices in the catalog
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Let’s have a simple look at the indices available. With the following *cURL* command, you see a list of the indices you can access: 

Simple JSON
'''''''''''

.. code-block:: console

  curl -u mrossi:ABcdEF "https://catalog.terradue.com"

The response is a JSON document with an array containing information about the indidces.

.. code-block:: json

    {
      "indices": [
          {
              "authors": [
                  {
                      "name": "Mario Rossi",
                      "mail": "mrossi@test.com"
                  }
              ],
              "created": "2016-06-03T10:30:42.7708920Z",
              "description": "Index containing the entries of the datasets published and saved by Mario Rossi.",
              "indexName": "mrossi",
              "lastMigrated": "2016-06-03T10:30:42.6951710Z",
              "version": 2
          },
          {
              "authors": [
                  {
                      "name": "Terradue DevOps team",
                      "uri": "https://www.terradue.com"
                  }
              ],
              "created": "2016-06-03T10:30:42.7708920Z",
              "description": "Index containing the entries of the datasets of Landsat-8 American Earth observation satellite launched on February 11, 2013. It is the eighth satellite in the Landsat program.",
              "indexName": "landsat8",
              "lastMigrated": "2016-06-03T10:30:42.6951710Z",
              "version": 2
          },
          {
              "authors": [
                  {
                      "name": "Terradue DevOps team",
                      "uri": "https://www.terradue.com"
                  }
              ],
              "created": "2016-06-03T10:30:42.7708920Z",
              "description": "Index containing the entries of the datasets of Envisat. Envisat was launched as an Earth observation satellite. Its objective was to service the continuity of European Remote-Sensing (ERS) Satellite missions, providing additional observational parameters to improve environmental studies.",
              "indexName": "envisat",
              "lastMigrated": "2016-06-03T10:30:42.6951710Z",
              "version": 2
          },
          {
              "authors": [
                  {
                      "name": "Terradue DevOps team",
                      "uri": "https://www.terradue.com"
                  }
              ],
              "created": "2016-06-03T10:30:42.7708920Z",
              "description": "Index containing the entries of the datasets of Sentinel-1 space mission funded by the European Union and carried out by the ESA within the Copernicus Programme.",
              "indexName": "sentinel1",
              "lastMigrated": "2016-06-03T10:30:42.6951710Z",
              "version": 2
          },
          {
              "authors": [
                  {
                      "name": "Terradue DevOps team",
                      "uri": "https://www.terradue.com"
                  }
              ],
              "created": "2016-06-03T10:30:42.7708920Z",
              "description": "Index containing the entries of the datasets of Sentinel-2. Sentinel-2 is an Earth observation mission developed by ESA as part of the Copernicus Programme to perform terrestrial observations in support of services such as forest monitoring, land cover changes detection, and natural disaster management.",
              "indexName": "sentinel2",
              "lastMigrated": "2016-06-03T10:30:42.6951710Z",
              "version": 2
          }
      ]
  }


OpenSearch
''''''''''

Alternatively, the indices can be queried using :ref:`opensearch-client-1` with :ref:`base syndication model <syndicationmetadatamodel>` and filtered.

.. code-block:: console

  opensearch-client -u mrossi:ABcdEF "https://catalog.terradue.com/search" identifier

And the response is the following list of identifiers:

.. code-block:: console-output

  sentinel1
  landsat8
  mrossi

  

Exploring series in the indices
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Indices can define subset of the entries they contain called :ref:`series`. The series can be discovered this way using *cURL*.

.. code-block:: console

    curl "https://catalog.terradue.com/mrossi/series/search"

This command will return an atom feed with all the series in the indices *mrossi*.


The same command with *opensearch-client* and a few more parameter allows to find the link to search then in the series themselves:

.. code-block:: console

    opensearch-client "https://catalog.terradue.com/mrossi/series/search" title,describes

    

Exploring data packages in the portal
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

You also can discover all the :ref:`data packages <datapackage>` available from the portal.

.. code-block:: console

    curl "<portal_api_url>/data/package/search?q=etna"


This command will return an atom feed with all the data packages where there is mentionned "etna" in the title, keywords, tags or content.


The same command with *opensearch-client* and a few more parameter allows to find the link to search then in the data packages themselves:

.. code-block:: console

    opensearch-client "<portal_api_url>/data/package/search?q=etna" title,describes


This returns for instance

.. code-block:: console

    Etna November 2014,<portal_api_url>/data/package/etnanov2014/search


Then you can :ref:`search <search>` in the found data package using the returned URL.