.. _downloading:

Downloading
===========

The download interface is implemented following the `Web Coverage Service (WCS)
<https://www.ogc.org/standards/wcs>`_ as well as the `Download Service for Earth
Observation Products Best Practice (DSEO)
<https://portal.opengeospatial.org/files/?artifact_id=55210>`_ standards.

These interfaces support both, the simple download of entire products via DSEO
as well as flexible customized downloads via WCS. Both services can be accessed
at the path ``/ows?``.

The WCS offers the following customizations in order to optimize downloads and
minimize unnecessarily used bandwidth:

* `Earth Observation Application Profile (EO-WCS)
  <http://docs.opengeospatial.org/is/10-140r2/10-140r2.html>`_
* Meaningful default configuration
* Spatial subset to retrieve only the geographic area of interest
* Range subset to retrieve only the band(s) of interest
* Scaling to required resolution
* Format selection
* Interpolation selection if needed
* Projection selection

Note that the download size in WCS is restricted in order to not block the
service. Clients are advised to download bigger coverages in chunks and put them
together afterwards.

Downloading in QGIS
-------------------

In order to use the download via WCS 1.0, that QGIS supports, a WCS layer needs to be added.

Open the Data Source Manager and add a WCS Layer, configuring the URL as shown in :numref:`fig_wcs_qgis1` and create a new WCS Connection using the URL of the service and specifying the product id to be downloaded via CQL= query. It is necessary to tick the **Ignore GetCoverage URI reported in capabilities**, as the reference URI usually does not contain the additional CQL or any other request parameters.

.. _fig_wcs_qgis1:
.. figure:: images/wcs_qgis1.*
   :alt: QGIS - Create WCS Connection

   *QGIS - Create WCS Connection*

A user can be prompted to specify the transformation between coordinate reference systems in case that the default output image is in a different coordinate reference system than current map projection - as shown in :numref:`fig_wcs_qgis2`

.. _fig_wcs_qgis2:
.. figure:: images/wcs_qgis2.*
   :alt: QGIS - CRS transformation confirmation

   *QGIS - CRS transformation confirmation*

Currently, QGIS supports specifying the output coordinate reference system and image format through the relevant input fields as shown in :numref:`fig_wcs_qgis3`. All other optional parameters for WCS request need to be added to the URL manually clicking on Edit button.

.. _fig_wcs_qgis3:
.. figure:: images/wcs_qgis3.*
   :alt: QGIS WCS layer options

   *QGIS WCS layer options*

The final chapter :ref:`sample_requests` holds a list of sample requests against
the various services described in this user guide.