OGC API - Tiles and its refinement at the 2020 Sprint


OGC API - Tiles: A simple method to serve any tiled resource over the web
Sprint demonstration of OGC API - Tiles delivering tiles across Time and Altitude Dimensions within within Hexagon Geospatial's LuciadLightspeed. Full size image here.

Further testing and refinement to the OGC API - Tiles candidate standard - the spiritual successor to one of OGC’s most popular standards, the Web Map Tile Service (WMTS) - has occurred during another successful OGC Sprint. The candidate standard is just one of several efforts forming OGC’s move towards modular, resource-oriented, OpenAPI-based standards.

The Move to OGC APIs

Application Programming Interfaces (APIs) are now a key way that data is published to the web, and a key component of rapid software development. There is now a multitude of APIs out there, but little-to-no standardization. This has resulted in interoperability issues when using multiple APIs to access data from different sources, wasting time, resources, and causing unnecessary headaches for users. The OGC API family of standards addresses this key requirement, simplifying access to, and increasing the usability of, location information across the web.

A key aspect of the development of OGC APIs is that they are modular. The core elements common to all OGC APIs are defined in the draft OGC API - Common standard, with specific functionality for different resources and data types being outlined in other OGC API specifications, such as OGC API - Tiles, OGC API - MapsOGC API - Features etc, that extend OGC API - Common. This creates not only modularity in deployment, with the developer being able to pick and choose the functionality they need for their service, but also consistency between different services and resources.

Simplifying Sharing Tiles

While, conceptually, OGC API - Tiles addresses the same need that initially birthed the WMTS standard - that is, the desire to share pre-tiled maps across the web - functionally, OGC API - Tiles offers much more. 

First of all, like all OGC APIs, the OGC API - Tiles candidate standard is designed to be as developer-friendly as possible, with the aim of being usable by a broader audience than the ‘traditional geospatial’ crowd. Secondly, the candidate standard specifies the necessary requirements for building an API that follows the resource-oriented approach of contemporary Web architecture - in particular the W3C/OGC best practices for sharing Spatial Data on the Web and the W3C best practices for sharing Data on the Web. This means that OGC APIs are not only immediately familiar to web developers, but are also indexable by search engines.

Additionally, the OGC API - Tiles candidate standard allows for APIs that can serve any tiled resource over the Web. Whereas WMTS focused on map tiles, OGC API - Tiles has been designed to support any form of tiled data, including map tiles, tiled feature data (e.g. vector tiles), tiled gridded coverages, and other tiled data. This creates a consistent way to retrieve any of these types of datasets (and one that is also consistent with other OGC APIs). Moreover, this provides the means to implement APIs by integrating multiple building blocks into a single solution that addresses the needs of different end users. This comes with several benefits:

  • For Developers, it means a single code base can serve map tiles, vector tiles, and other tiled data, which saves development and maintenance time and makes it easier to develop new capabilities.
  • For a Systems Administrator, greater efficiency is gained from managing, securing, and maintaining a single deployment or endpoint.

Finally, the OGC API - Tiles (as well as the other OGC API standards) candidate standard is extensible, so that any functionality required by more specific use-cases, or shifts in preferred technologies, can be added without breaking compatibility with the core standard.

Demonstration of OGC API - Tiles delivering vector tiles of 500m elevation contours in the Himalayas within Ecere's GNOSIS Map Server. Full size image here.

Further development & testing at the OGC API - Tiles Sprint

In making sure that all OGC APIs are as developer-friendly, usable, and mature as possible before release, all OGC APIs are being put through Sprints to test and improve their ‘readiness’ before starting the OGC approval process. An OGC Sprint is a collaborative and inclusive event driven by innovative and rapid programming with minimal process and organization constraints to support the development of new applications and open standards. 

The OGC API - Tiles Sprint was held from 23rd to 24th April, 2020, organized by OGC and sponsored by Ordnance Survey. The sprint, held completely virtually, brought together software developers and solution architects to experiment with and validate the current OGC API - Tiles candidate standard. 

The objectives of the OGC API - Tiles Sprint were to:

  1. Develop implementations of OGC API - Tiles
  2. Test implementations of OGC API - Tiles
  3. Provide feedback on the specification

“As a Strategic Member of OGC, Ordnance Survey is pleased to continue supporting the development of the next generation of OGC API standards,” said Michael Gordon, Strategic Product Manager at Ordnance Survey. “The OGC API - Tiles Sprint made substantial progress on the candidate standard, with many participants focusing on future extensions of the core standard - demonstrating stability and support for the core standard, as well as its extensibility, for instance to 3D and 4D data. This continues to ensure that the next generation of OGC APIs are developer-friendly, easy to use, and follow web and geospatial best practice.”

The sprint showed that the draft OGC API - Tiles specification has reached a stage of maturity where it is implementable and developer friendly. Indeed, over the two-day virtual event there were nine demonstrations of implementations of the candidate standard. Among the demonstrations were: a contour map draped over a Digital Elevation Model (DEM) in a 3D visualization, a 3D Globe visualization created using a draft Tile Matrix Set for the British National Grid projected coordinate reference system; and a visualization demonstrating how OGC API - Tiles could support a temporal dimension. The demonstrations enabled developers to provide instant feedback to the editors of the candidate standard.

“We were not able to spot any fundamental flaws in the OGC API approach while we demonstrated that the candidate standard can be implemented,” said Joan Masó, CREAF, and Co-chair of the OGC WMS Standards Working Group, which is developing the OGC API - Tiles standard. “We were also able to demonstrate that an approach based on building blocks is feasible. In the building block approach, standards can complement each other, but they make an effort to avoid strict dependencies between them. This allows the same building block to be used in different configurations. We still have to work on many details, but we are confident that we can reach the Request for Public Comment phase for OGC API - Tiles very soon.”

The participants worked together to develop, deploy, and test new OGC API - Tiles implementations from diverse organizations from across the private, public, and academic sectors. In undertaking this, the participants identified a number of areas to improve the candidate standard. The candidate standard will therefore be revised over the next few months before release of the draft for public comment.

OGC Members who wish to contribute to, or keep abreast of, the development of the OGC API - Tiles standard are welcome to join the OGC WMS Standards Working Group, the OGC API - Tiles GitHub page, or follow along at the OGC Standards Roadmap
More information on the Sprint (as well as other OGC Sprints) is available on the OGC Sprints page, or on the OGC API - Tiles Sprint GitHub page. Learn more about OGC’s emerging family of APIs at ogcapi.ogc.org.