GSoC 2020 CQL filter implementation on pygeoapi

Introduction

Idea

pygeoapi, is a Python server implementation of the OGC API suite of standards. OGC API standards define modular API building blocks to spatially enable Web API in a consistent way. This standard specifies the fundamental API building blocks for interacting with features. OGC API Features provides API building blocks to create, modify and query features of geospatial data collection on the Web.

A fundamental operation performed on a collection of features is that of querying in order to obtain a subset of the data which contains feature instances that satisfy some filtering criteria. This project aims to implement these enhanced filtering criteria in a request to a server. CQL will be used to specify how resource instances in a source collection should be filtered to identify a result set. Typically, CQL is used in query operations to identify the subset of resources that should be included in a response document. Each resource instance in the source collection is evaluated using a filtering expression. The overall filter expression always evaluates to true or false. If the expression evaluates to true, the resource instance satisfies the expression and is marked as being in the result set. If the overall filter expression evaluates to false, the data instance is not in the result set.

The project proposal is based on OGC API - Features - Part 3: Common Query Language document that defines the schema for a JSON document that exposes the set of properties or keys that may be used to construct CQL expressions for pygeoapi.

Project proposal

My proposal for GSoC 2020 can be found at: Proposal.

Advantages from this project

On developing CQL feature filter implementation with JSON encoding, any combination of bbox, datetime and parameters for filtering on feature properties will be allowed on pygeoapi. The requirements on these parameters imply that only features matching all the predicates are in the result set. i.e., the logical operator between the predicates is 'AND'. The API definition may be used to determine details, e.g., on filter parameters. This depends on the needs of the client. These are clients that are in general able to use multiple APIs as long as it implements OGC API Features. Thus increases the client’s usage capabilities.

Link to Github repository: Repository

Timeline

5th May - 31st May

Community bonding period:

1. What I have done during this period?

• Introduced myself over the channel and shared my proposal over mailing list for suggestions
• Communicated with mentors and learned about community, working, etc. It was a great experience talking with experts in the domain
• Created a wiki page for the project "Develop CQL Filter implementation for pygeoapi"
• Forked the repository of pygeoapi Repository
• Updated wiki User page and added my personal information User
• Updated links on the wiki Google_Summer_of_Code_2020_Accepted page Link
• Joined Gitter account created by mentors which we will be used as a mode of communication over the GSoC 2020 period
• Gone through the architecture and codebase of pygeoapi
• Read OGC API - Features - Part 1: Core OGC API - Features - Part 3: Common Query Language documents to understand the standards of OGC API.
• Understood the implementation of CQL schema and standards
• Learned to work with python CQL parser pycql.
• Discussed with the mentors about their expectations over the GSoC 2020 project period

Student's Biography

Farheen is a strong engineering professional with a B.Tech focused in Computer Science Engineering from West Bengal University of Technology, Kolkata, India. Currently she is pursuing M.Tech in Geo-informatics and Natural Resource Engineering under Centre of Studies in Resources Engineering from Indian Institute of Technology Bombay, Mumbai, India. Some more information about me can be obtained by following the link: User

Mentors

• Francesco Bartoli Bartoli
• Jorge Samuel Mendes de Jesus Samuel Mendes de Jesus