Customizing pygeoapi: plugins

In this section we will explain how pygeoapi provides plugin architecture for data providers, formatters and processes.

Plugin development requires knowledge of how to program in Python as well as Python’s package/module system.

Overview

pygeoapi provides a robust plugin architecture that enables developers to extend functionality. Infact, pygeoapi itself implements numerous formats, data providers and the process functionality as plugins.

The pygeoapi architecture supports the following subsystems:

  • data providers

  • output formats

  • processes

The core pygeoapi plugin registry can be found in pygeoapi.plugin.PLUGINS.

Each plugin type implements its relevant base class as the API contract:

  • data providers: pygeoapi.provider.base

  • output formats: pygeoapi.formatter.base

  • processes: pygeoapi.process.base

Todo

link PLUGINS to API doc

Plugins can be developed outside of the pygeoapi codebase and be dynamically loaded by way of the pygeoapi configuration. This allows your custom plugins to live outside pygeoapi for easier maintenance of software updates.

Note

It is recommended to store pygeoapi plugins outside of pygeoapi for easier software updates and package management

Example: custom pygeoapi data provider

Lets consider the steps for a data provider plugin (source code is located here: Provider).

Python code

The below template provides a minimal example (let’s call the file mycooldata.py:

from pygeoapi.provider.base import BaseProvider

class MyCoolDataProvider(BaseProvider):
    """My cool data provider"""

    def __init__(self, provider_def):
        """Inherit from parent class"""

        BaseProvider.__init__(self, provider_def)

    def get_fields(self):

        # open dat file and return fields and their datatypes
        return {
            'field1': 'string',
            'field2': 'string'
        }

    def query(self, startindex=0, limit=10, resulttype='results',
              bbox=[], datetime=None, properties=[], sortby=[]):

        # open data file (self.data) and process, return
        return {
            'type': 'FeatureCollection',
            'features': [{
                'type': 'Feature',
                'id': '371',
                'geometry': {
                    'type': 'Point',
                    'coordinates': [ -75, 45 ]
                },
                'properties': {
                    'stn_id': '35',
                    'datetime': '2001-10-30T14:24:55Z',
                    'value': '89.9'
                }
            }]
        }

For brevity, the above code will always return the single feature of the dataset. In reality, the plugin developer would connect to a data source with capabilities to run queries and return relevant a result set, as well as implement the get method accordingly. As long as the plugin implements the API contract of its base provider, all other functionality is left to the provider implementation.

Each base class documents the functions, arguments and return types required for implementation.

Connecting to pygeoapi

The following methods are options to connect the plugin to pygeoapi:

Option 1: Update in core pygeoapi:

  • copy mycooldata.py into pygeoapi/provider

  • update the plugin registry in pygeoapi/plugin.py:PLUGINS['provider'] with the plugin’s shortname (say MyCoolData) and dotted path to the class (i.e. pygeoapi.provider.mycooldata.MyCoolDataProvider)

  • specify in your dataset provider configuration as follows:

provider:
    name: MyCoolData
    data: /path/to/file
    id_field: stn_id

Option 2: implement outside of pygeoapi and add to configuration (recommended)

  • create a Python package of the mycooldata.py module (see Cookiecutter as an example)

  • install your Python package onto your system (python setup.py install). At this point your new package should be in the PYTHONPATH of your pygeoapi installation

  • specify in your dataset provider configuration as follows:

provider:
    name: mycooldatapackage.mycooldata.MyCoolDataProvider
    data: /path/to/file
    id_field: stn_id

Example: custom pygeoapi formatter

Python code

The below template provides a minimal example (let’s call the file mycooljsonformat.py:

import json
from pygeoapi.formatter.base import BaseFormatter

class MyCoolJSONFormatter(BaseFormatter):
    """My cool JSON formatter"""

    def __init__(self, formatter_def):
        """Inherit from parent class"""

        BaseFormatter.__init__(self, {'name': 'cooljson', 'geom': None})
        self.mimetype = 'text/json; subtype:mycooljson'

    def write(self, options={}, data=None):
        """custom writer"""

        out_data {'rows': []}

        for feature in data['features']:
            out_data.append(feature['properties'])

        return out_data

Processing plugins

Processing plugins are following the OGC API - Processes development. Given that the specification is under development, the implementation in pygeoapi/process/hello_world.py provides a suitable example for the time being.