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
process manager
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
process_manager:
pygeoapi.process.manager.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
Connecting plugins to pygeoapi
The following methods are options to connect a plugin to pygeoapi:
Option 1: implement outside of pygeoapi and add to configuration (recommended)
Create a Python package with the plugin code (see Cookiecutter as an example)
Install this Python package onto your system (
python3 setup.py install
). At this point your new package should be in thePYTHONPATH
of your pygeoapi installationSpecify the main plugin class as the
name
of the relevant type in the pygeoapi configuration. For example, for a new vector data provider:
providers:
- type: feature
# name may refer to an external Python class, that is loaded by pygeoapi at runtime
name: mycooldatapackage.mycoolvectordata.MyCoolVectorDataProvider
data: /path/to/file
id_field: stn_id
Specifying custom pygeoapi CLI commands
Third-party plugins may also provide custom CLI commands. This can be done by means of two additional steps:
Create your CLI commands using click
In your plugin’s
setup.py
orpyproject.toml
file, specify an entrypoint for thepygeoapi
group pointing to your click CLI command or group.
As a simple example, lets imagine you develop a plugin named myplugin
, which has a cli.py
module with
the following contents:
# module: myplugin.cli
import click
@click.command(name='super-command')
def my_cli_command():
print('Hello, this is my custom pygeoapi CLI command!')
Then, in your plugin’s setup.py
file, specify the entrypoints section:
# file: setup.py
entry_points={
'pygeoapi': ['my-plugin = myplugin.cli:my_cli_command']
}
Alternatively, if using a pyproject.toml
file instead:
# file: pyproject.toml
# Noter that this example uses poetry, other Python projects may differ in
# how they expect entry_points to be specified
[tool.poetry.plugins.'pygeoapi']
my-plugin = 'myplugin.cli:my_cli_command'
After having installed this plugin, you should now be able to call the CLI command by running:
$ pygeoapi plugins super-command
Hello, this is my custom pygeoapi CLI command!
Note
The United States Geological Survey has created a Cookiecutter project for creating pygeoapi plugins. See the pygeoapi-plugin-cookiecutter project to get started.
Option 2: Update in core pygeoapi:
Copy your plugin code into the pygeoapi source code directory - for example, if it is a provider plugin, copy it to
pygeoapi/provider
Update the plugin registry in
pygeoapi/plugin.py:PLUGINS['provider']
with the plugin’s shortname (sayMyCoolVectorData
) and dotted path to the class (i.e.pygeoapi.provider.mycoolvectordata.MyCoolVectorDataProvider
)Specify in your dataset provider configuration as follows:
providers:
- type: feature
# name may also refer to a known core pygeopai plugin
name: MyCoolVectorData
data: /path/to/file
id_field: stn_id
Customizing pygeoapi process manager
The pygeoapi process manager may also be customized. Similarly to the provider plugins, you may use the pygeoapi
configuration’s server.manager.name
to indicate either the dotted path to the python package and the relevant
manager class (i.e. similar to option 1 above) or the name of a known core pygeoapi plugin (i.e., similar to
option 2 above).
Example: custom pygeoapi vector data provider
Lets consider the steps for a vector data provider plugin:
Python code
The below template provides a minimal example (let’s call the file mycoolvectordata.py
:
from pygeoapi.provider.base import BaseProvider
class MyCoolVectorDataProvider(BaseProvider):
"""My cool vector data provider"""
def __init__(self, provider_def):
"""Inherit from parent class"""
super().__init__(provider_def)
def get_fields(self):
# open dat file and return fields and their datatypes
return {
'field1': 'string',
'field2': 'string'
}
def query(self, offset=0, limit=10, resulttype='results',
bbox=[], datetime_=None, properties=[], sortby=[],
select_properties=[], skip_geometry=False, **kwargs):
# optionally specify the output filename pygeoapi can use as part
# of the response (HTTP Content-Disposition header)
self.filename = 'my-cool-filename.dat'
# 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'
}
}]
}
def get_schema():
# return a `dict` of a JSON schema (inline or reference)
return ('application/geo+json', {'$ref': 'https://geojson.org/schema/Feature.json'})
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 a relevant 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.
Note
You can add language support to your plugin using these guides.
Note
You can let the pygeoapi core do coordinate transformation for crs queries using the @crs_transform Decorator on query() and get() methods. See CRS support.
Example: custom pygeoapi raster data provider
Lets consider the steps for a raster data provider plugin:
Python code
The below template provides a minimal example (let’s call the file mycoolrasterdata.py
:
from pygeoapi.provider.base import BaseProvider
class MyCoolRasterDataProvider(BaseProvider):
"""My cool raster data provider"""
def __init__(self, provider_def):
"""Inherit from parent class"""
super().__init__(provider_def)
self.num_bands = 4
self.axes = ['Lat', 'Long']
self.get_fields()
def get_fields(self):
# generate a JSON Schema of coverage band metadata
self._fields = {
'b1': {
'type': 'number'
}
}
return self._fields
def query(self, bands=[], subsets={}, format_='json', **kwargs):
# process bands and subsets parameters
# query/extract coverage data
# optionally specify the output filename pygeoapi can use as part
of the response (HTTP Content-Disposition header)
self.filename = 'my-cool-filename.dat'
if format_ == 'json':
# return a CoverageJSON representation
return {'type': 'Coverage', ...} # trimmed for brevity
else:
# return default (likely binary) representation
return bytes(112)
For brevity, the above code will always return JSON for metadata and binary or CoverageJSON for the data. In reality, the plugin developer would connect to a data source with capabilities to run queries and return a relevant result set, 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.
Example: custom pygeoapi processing plugin
Let’s consider a simple process plugin to calculate a square root from a number:
Python code
The below template provides a minimal example (let’s call the file mycoolsqrtprocess.py
:
import math
from pygeoapi.process.base import BaseProcessor, ProcessorExecuteError
PROCESS_METADATA = {
# reduced for brevity (see examples of PROCESS_METADATA in pygeoapi/process/hello_world.py)
}
class MyCoolSqrtProcessor(BaseProcessor)
"""My cool sqrt process plugin"""
def __init__(self, processor_def):
"""
Initialize object
:param processor_def: provider definition
:returns: pygeoapi.process.mycoolsqrtprocess.MyCoolSqrtProcessor
"""
super().__init__(processor_def, PROCESS_METADATA)
def execute(self, data):
mimetype = 'application/json'
number = data.get('number')
if number is None:
raise ProcessorExecuteError('Cannot process without a number')
try:
number = float(data.get('number'))
except TypeError:
raise ProcessorExecuteError('Number required')
value = math.sqrt(number)
outputs = {
'id': 'sqrt',
'value': value
}
return mimetype, outputs
def __repr__(self):
return f'<MyCoolSqrtProcessor> {self.name}'
The example above handles a dictionary of the JSON payload passed from the client, calculates the square root of a float or integer, and returns the result in an output JSON payload. The plugin is responsible for defining the expected inputs and outputs in PROCESS_METADATA
and to return the output in any format along with the corresponding media type.
Note
Additional processing plugins can also be found in pygeoapi/process
.
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"""
super().__init__({'name': 'cooljson', 'geom': None})
self.mimetype = 'application/json; subtype:mycooljson'
def write(self, options={}, data=None):
"""custom writer"""
out_data = {'rows': []}
for feature in data['features']:
out_data['rows'].append(feature['properties'])
return out_data
Featured plugins
Community based plugins can be found on the pygeoapi Community Plugins and Themes wiki page.