.. _ogcapi-processes:

Publishing processes via OGC API - Processes
============================================

`OGC API - Processes`_ provides geospatial data processing functionality in a standards-based
fashion (inputs, outputs).

pygeoapi implements OGC API - Processes functionality by providing a plugin architecture, thereby
allowing developers to implement custom processing workflows in Python.

The pygeoapi offers two processes: a default ``hello-world`` process which allows you to quickly explore the capabilities of processes, and an optional ``shapely-functions`` process with more advanced features that leverages `Shapely`_ to expose various geometric processing functionality.

Configuration
-------------

.. code-block:: yaml

   processes:
   
    # enabled by default
       hello-world:
           processor:
               name: HelloWorld

Asynchronous support
--------------------

By default, pygeoapi implements process execution (jobs) as synchronous mode.  That is, when
jobs are submitted, the process is executed and returned in real-time.  Certain processes
that may take time to execute, or be delegated to a scheduler/queue, are better suited to
an asynchronous design pattern.  This means that when a job is submitted in asynchronous
mode, the server responds immediately with a reference to the job, which allows the client
to periodically poll the server for the processing status of a given job.

pygeoapi provides asynchronous support by providing a 'manager' concept which, well,
manages job execution.  The manager concept is implemented as part of the pygeoapi
:ref:`plugins` architecture.  pygeoapi provides a default manager implementation
based on `TinyDB`_ for simplicity.  Custom manager plugins can be developed for more
advanced job management capabilities (e.g. Kubernetes, databases, etc.).

In keeping with the OGC API - Processes specification, asynchronous process execution
can be requested by including the ``Prefer: respond-async`` HTTP header in the request


.. code-block:: yaml

   server:
       manager:
           name: TinyDB
           connection: /tmp/pygeoapi-process-manager.db
           output_dir: /tmp/

MongoDB
--------------------
As an alternative to the default a manager employing `MongoDB`_ can be used. 
The connection to an installed `MongoDB`_ instance must be provided in the configuration.
`MongoDB`_ uses the localhost and port 27017 by default. Jobs are stored in a collection named
job_manager_pygeoapi.

.. code-block:: yaml

   server:
       manager:
           name: MongoDB
           connection: mongodb://host:port
           output_dir: /tmp/


Putting it all together
-----------------------

To summarize how pygeoapi processes and managers work together::

* process plugins implement the core processing / workflow functionality
* manager plugins control and manage how processes are executed

Processing examples
-------------------

Hello World (Default)
^^^^^^^^^^^^^^^^^^^^^

.. code-block:: sh

   # list all processes
   curl http://localhost:5000/processes

   # describe the ``hello-world`` process
   curl http://localhost:5000/processes/hello-world

   # show all jobs
   curl http://localhost:5000/jobs

   # execute a job for the ``hello-world`` process
   curl -X POST http://localhost:5000/processes/hello-world/execution \
       -H "Content-Type: application/json" \
       -d "{\"inputs\":{\"name\": \"hi there2\"}}"

   # execute a job for the ``hello-world`` process with a raw response (default)
   curl -X POST http://localhost:5000/processes/hello-world/execution \
       -H "Content-Type: application/json" \
       -d "{\"inputs\":{\"name\": \"hi there2\"}}"

   # execute a job for the ``hello-world`` process with a response document
   curl -X POST http://localhost:5000/processes/hello-world/execution \
       -H "Content-Type: application/json" \
       -d "{\"inputs\":{\"name\": \"hi there2\"},\"response\":\"document\"}"

   # execute a job for the ``hello-world`` process in asynchronous mode
   curl -X POST http://localhost:5000/processes/hello-world/execution \
       -H "Content-Type: application/json" \
       -H "Prefer: respond-async" \
       -d "{\"inputs\":{\"name\": \"hi there2\"}}"
   # execute a job for the ``hello-world`` process with a success subscriber
    curl -X POST http://localhost:5000/processes/hello-world/execution \
        -H "Content-Type: application/json" \
        -d "{\"inputs\":{\"name\": \"hi there2\"}, \
            \"subscriber\": {\"successUri\": \"https://www.example.com/success\"}}"

Shapely Functions (Optional)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The `shapely-functions` process exposes some selected Shapely_ functions as sample process. The selection cut across different operations in Shapely. To avoid function collision, it uses the name of the function category as the namespace. E.g *union* operation under the *set* module is described as *set:union*.

The process is configured to accept a list of geometry *inputs* (WKT and/or GeoJSON geometry), *operation*  and an optional *output_format*. It performs the specified operation and returns the result in the specified *output_format* (If the operation does not return a geometry, then this is ignored).


Configuration
-------------

.. code-block:: yaml

   processes:
        shapely-functions:
           processor:
               name: ShapelyFunctions


**Supported operations**

* **measurement:bounds** - Computes the bounds (extent) of a geometry.
* **measurement:area** - Computes the area of a (multi)polygon.
* **measurement:distance** - Computes the Cartesian distance between two geometries.
* **predicates:covers** - Returns True if no point in geometry B is outside geometry A.
* **predicates:within** - Returns True if geometry A is completely inside geometry B.
* **set:difference** - Returns the part of geometry A that does not intersect with geometry B.
* **set:union** - Merges geometries into one.
* **constructive:buffer** - Computes the buffer of a geometry for positive and negative buffer distance.
* **constructive:centroid** - Computes the geometric center (center-of-mass) of a geometry.
 
**Limitation**

There is no support for passing optional function arguments yet. E.g when computing buffer on a geometry, no option to pass in the buffer distance.

.. code-block:: sh

   # describe the ``shapely-functions`` process
   curl http://localhost:5000/processes/shapely-functions

   # execute a job for the ``shapely-functions`` process that computes the bounds of a WKT
   curl -X POST http://localhost:5000/processes/shapely-functions/execution \
       -H "Content-Type: application/json" \
       -d "{\"inputs\":{\"operation\": \"measurement:bounds\",\"geoms\": [\"POINT(83.27651071580385 22.593553859283745)\"]}}"

   # execute a job for the ``shapely-functions`` process that calculates the area of a WKT Polygon 
   curl -X POST http://localhost:5000/processes/shapely-functions/execution \
       -H "Content-Type: application/json" \
       -d "{\"inputs\":{\"operation\": \"measurement:area\",\"geoms\": [\"POLYGON ((0 0, 1 0, 1 1, 0 1, 0 0))\"]}}"
   
   # execute a job for the ``shapely-functions`` process that calculates the distance between two WKTs
   curl -X POST http://localhost:5000/processes/shapely-functions/execution \
       -H "Content-Type: application/json" \
       -d "{\"inputs\":{\"operation\": \"measurement:distance\",\"geoms\": [\"POLYGON ((0 0, 1 0, 1 1, 0 1, 0 0))\",\"POINT(83.27651071580385 22.593553859283745)\"]}}"
   
   # execute a job for the ``shapely-functions`` process that calculates the predicate difference between two WKTs and returns a GeoJSON feature
   curl -X POST http://localhost:5000/processes/shapely-functions/execution \
       -H "Content-Type: application/json" \
       -d "{\"inputs\":{\"operation\": \"set:difference\",\"geoms\": [\"POLYGON ((0 0, 1 0, 1 1, 0 1, 0 0))\",\"POINT(83.27651071580385 22.593553859283745)\"],\"output_format\":\"geojson\"}}"
   
   # execute a job for the ``shapely-functions`` process that calculates the predicate difference between two WKTs and returns a WKT
   curl -X POST http://localhost:5000/processes/shapely-functions/execution \
       -H "Content-Type: application/json" \
       -d "{\"inputs\":{\"operation\": \"set:difference\",\"geoms\": [\"POLYGON ((0 0, 1 0, 1 1, 0 1, 0 0))\",\"POINT(83.27651071580385 22.593553859283745)\"],\"output_format\":\"wkt\"}}"

   # execute a job for the ``shapely-functions`` process that computes the buffer of a GeoJSON feature and returns a WKT 
   curl -X POST http://localhost:5000/processes/shapely-functions/execution \
       -H "Content-Type: application/json" \
       -d "{\"inputs\":{\"operation\": \"constructive:buffer\",\"geoms\": [{\"type\": \"LineString\",\"coordinates\": [[102.0,0.0],[103.0, 1.0],[104.0,0.0]]}],\"output_format\":\"wkt\"}}"


.. _`OGC API - Processes`: https://ogcapi.ogc.org/processes
.. _`sample`: https://github.com/geopython/pygeoapi/blob/master/pygeoapi/process/hello_world.py
.. _`shapely_functions`: https://github.com/geopython/pygeoapi/blob/master/pygeoapi/process/shapely_functions.py
.. _`TinyDB`: https://tinydb.readthedocs.io/en/latest
.. _`Shapely`: https://shapely.readthedocs.io/