pg-to-evalscript 0.2.1

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openEO process graph to evalscript converter

This repository contains a library for converting openEO process graphs to Sentinel Hub evalscripts.

The motivation behind this library is to reduce the data transfer between the SH backend and the openEO backend and to move part of the processing directly to backend where the data is stored.

API

convert_from_process_graph

convert_from_process_graph(
    process_graph,
    n_output_bands=1,
    sample_type="FLOAT32",
    units=None,
    bands_dimension_name="bands",
    temporal_dimension_name="t",
    bands_metadata=[]
)

Parameters

• process_graph: dict

  OpenEO process graph JSON as Python dict object.

• n_output_bands: int, optional. Default: 1

  Number of output bands in the evalscript. This can be set if the value is known beforehand. See docs.

• sample_type: str, optional. Default: FLOAT32

  Desired sampleType of the output raster. See possible values.

• units: str, optional. Default: None

  Units used by all the bands in the evalscript. If None, units evalscript parameter isn't set and default units for each band are used. See docs.

• bands_dimension_name: str, optional. Default: bands

  Name of the default dimension of type bands of the datacube, as set in load_collection and referred to in the openEO process graph.

• temporal_dimension_name: str, optional. Default: t

  Name of the default dimension of type temporal of the datacube, as set in load_collection and referred to in the openEO process graph.

• bands_metadata: list, optional. Default: []

  List of metadata information for all bands of a certain collection.

• encode_result: bool, optional. Default: True

  Should the result of the evalscript be encoded with the dimensions of the data or returned as is.

Output

• evalscripts: list of dicts

  Returns a list of dicts containing the Evalscript objects. Every element consists of:

  • invalid_node_id: Id of the first invalid node after a supported subgraph. The output of the associated evalscript should be the input of the node. If it is None, the entire graph is valid.

  • evalscript: instance of and Evalscript object that generates an evalscript for a valid subgraph from load_collection to the node with id invalid_node_id.

Evalscript

Constructor parameters

• input_bands: list

  List of bands to be imported. See docs.

• nodes: list

  List of Node objects that constitute the valid process (sub)graph.

• initial_data_name: str

  The id of the initial load_collection node that loads the data.

• n_output_bands: int, optional. Default: 1

  Number of output bands in the evalscript. This can be set if the value is known beforehand. See docs.

• sample_type: str, optional. Default: FLOAT32

  Desired sampleType of the output raster. See possible values.

• units: str, optional. Default: None

  Units used by all the bands in the evalscript. If None, units evalscript parameter isn't set and default units for each band are used. See docs.

• mosaicking: str, optional. Default: ORBIT

  Works with multi-temporal data by default. See possible values.

• bands_dimension_name: str, optional. Default: bands

  Name of the default dimension of type bands of the datacube, as set in load_collection and referred to in the openEO process graph.

• temporal_dimension_name: str, optional. Default: t

  Name of the default dimension of type temporal of the datacube, as set in load_collection and referred to in the openEO process graph.

• datacube_definition_directory: str, optional. Default: javascript_datacube

  Relative path to the directory with the javascript implemetations of the processes.

• output_dimensions: list of dicts or None, optional. Default: None

  Information about the dimensions in the output datacube. This can be set if the value is known beforehand. Each element contains:

  • name: name of the dimension,
  • size: size (length) of the dimension,
  • original_temporal, optional: boolean, should be True if this is the temporal dimension generated in the initial load_collection node.

• encode_result: bool, optional. Default: True

  Should the result of the evalscript be encoded with the dimensions of the data or returned as is.

• bands_metadata: list, optional. Default: []

  List of metadata information for all bands of a certain collection.

Methods

• write():

  Returns the evalscript as a string.

• determine_output_dimensions():

  Calculates the greatest possible dimensions of the output datacube, returning a list of dicts. Each element contains:

  • name: name of the dimension,
  • size: size (length) of the dimension,
  • original_temporal, optional: boolean, True if this is the temporal dimension generated in the initial load_collection node.

• set_output_dimensions(output_dimensions):

  Setter for output dimensions. output_dimensions is a list of dicts. Each element contains:

  • name: name of the dimension,
  • size: size (length) of the dimension,
  • original_temporal, optional: boolean, should be True if this is the temporal dimension generated in the initial load_collection node.

• set_input_bands(input_bands):

  Setter for input bands. input_bands is an array of strings (band names) or None. Output dimensions are recalculated.

• get_decoding_function():

  Returns a decode_data function. The data returned by the evalscript is encoded to contain the information about the datacube dimensions and has to be decoded to obtain the actual data in a ndarray format. decode_data has the following parameters:

  • data: the result of processing of the associated evalscript, it should be a three-dimensional array. decode_data returns a multidimensional Python list.

list_supported_processes

Returns a list of process ids of supported openEO processes.

Workflow

1. Construct the openEO process graph

Load a file with json.load or generate an openEO process graph using openEO Python client.

2. Run the conversion

subgraph_evalscripts = convert_from_process_graph(process_graph)

print(subgraph_evalscripts)
>>> [{'evalscript': <pg_to_evalscript.evalscript.Evalscript object at 0x000001ABA779CA00>, 'invalid_node_id': None}]

In this example, the entire openEO process graph could be converted to an evalscript, so we only have one entry.

3. Fetch the data

evalscript = subgraph_evalscripts[0]['evalscript'].write()
print(evalscript)
>>> "//VERSION=3 function setup(){ ..."

The evalscript string can now be used to process data on Sentinel Hub. Sentinel Hub Python client makes it easy to do so.

4. Decode the fetched data

# Get the decoding function fo  r this evalsscript
decoding_function = evalscript.get_decoding_function()
# Pass the fetched data through the decoding function. 
# The function expects a python list. If you're using Sentinel Hub Python client, the result might be a numpy array, so it has to be converted.
decoded_data = decoding_function(fetched_data.tolist())
print(decoded_data)
>>> [[[1, 2, 3], [4, 5, 6], ... ]]

Running notebooks

pipenv install --dev --pre

Start the notebooks

cd notebooks
pipenv run jupyter notebook

Running tests

Using Docker

docker build -t tests .
docker run tests

Directly

Tests require a NodeJS environment.

pipenv install
pipenv shell
cd tests
pytest

Linting

pipenv run black -l 120 .

Benchmark

pipenv shell
cd tests
python benchmark.py

Developing

Install the package in editable mode so the changes take effect immediately.

pipenv install -e .