A New Look for the Portrayal of Geospatial Information
The past two years have seen several new initiatives in OGC to advance new standards and improve interoperability for portraying geospatial data – that is, defining methods to create consistency between maps from different providers. New approaches have been explored and demonstrated during OGC Innovation Program initiatives, including Testbed-14, Testbed-15, and currently Testbed-16, as well as the Vector Tiles Pilot. A new Portrayal Domain Working Group (DWG) was created in 2019, followed by the Styles API Standards Working Group (SWG) in 2020 and the recent recharter of the Styled Layer Descriptor (SLD) and Symbology Encoding (SE) SWG into a refocused Styles and Symbology Encoding SWG.
The cornerstone of the new portrayal efforts was the design of the Open Portrayal Framework (OPF) in Testbed 15 (see a previous blog post on that work here, or the OGC Testbed-15: Open Portrayal Framework Engineering Report here) and the documentation and approval of the Symbology Conceptual Model: Core Part (SymCore) standard.
OPF & SymCore: modularizing portrayal
Together, the OPF and the SymCore standard define a modern and modular approach to portrayal based on the intent to have many extensions from a common conceptual model and many encodings of those extensions. With this approach, a common symbology definition can be implemented in multiple encodings and easily shared by multiple clients to provide similar visualization effects to different users. The OPF helps to define a seamless online and offline experience that incorporates emerging OGC APIs for enhanced sharing of features and coverage data, images, and tiles for networked users and GeoPackages for disadvantaged and disconnected users.
The ability to implement multiple styles derived from a common model in different encodings is particularly useful for sharing styles across a community of interest or within large enterprises. While previous sharing solutions required embracing single vendor implementations or tailored styles suited to specific client and display environments, the work of recent and ongoing OGC initiatives now allows standardized modules for shared data formats and schemas, common symbology, and portrayal rules with multiple encodings that can provide a common operational picture with tailored views based on operational requirements and IT system constraints.
This framework allows a common approach for a diverse user community ranging from disadvantaged users on mobile devices with limited bandwidth to robust, well-networked, high-end GIS. This modular approach is adaptable to varied data formats and schemas while applying core rules and symbology to unique encodings.
Vector Tile Pilot similar display from different encodings and renderers. Source.
The ongoing work of the Styles API SWG and the rechartered Styles and Symbology Encoding SWG will enable the full realization of the Open Portrayal Framework. The Styles API SWG will develop a specification for an API to advertise and share available styles as resources to be shared and employed. Within the OGC API family, this will allow the geospatial user to access styles as needed to combine with data collections available from OGC APIs for Features, Coverages, Maps, or Tiles to provide the intended display appropriate for the system. As prototyped in the Innovation Program, the draft Styles API defines core capabilities for multiple styles, stylesheets, and stylable layer sets to be offered in multiple encodings as required by the geospatial enterprise. Future enhancements could allow for editing of styles for both unique user-defined styles and to update the style for the common operational picture.
The Styles and Symbol Encoding SWG will develop the extensions and encodings essential to implement SymCore as the styles needed to resource the Styles API and provide the open exchange to enable the Open Portrayal Framework. The basic requirements classes in SymCore need to be extended to fit domain-specific definitions essential to style development. Initial extensions are planned to support 2-dimensional and 3-dimensional features as well as coverage data. From these extensions, encoding specifications will be documented to support client and server rendering of styles in common software languages to include XML and JSON. Further extensions and encodings may be developed based on community interests and resources. Collaboration between the Styles and Symbol Encoding SWG and the GeoPackage SWG will work to define an SQL style encoding schema and a GeoPackage portrayal extension.
An exciting future for sharable styles and symbology
The recent events in the Innovation Program initiative, the Portrayal DWG and the Styles API and Styles and Symbology Encoding SWG only mark the first steps toward realizing the Open Portrayal Framework. Concepts and prototypes need to mature into specifications and implementations. Additional opportunities to mature and expand the OPF are anticipated, such as incorporating the 3D Portrayal standard with an API of GeoVolumes to expose 3D data and Style API resources to tile and portray multi-dimensional geospatial content. The outputs of these portrayal activities will provide the foundation for improved development, sharing, and application of styles in user environments and enterprises ranging from small enclosed GIS systems to large geospatial enterprises with robust network infrastructure and diverse systems to offline use by disconnected and disadvantaged users all operating from common, sharable styles with efficient API-driven interoperability. The new look of portrayal in OGC is just beginning.