Styles and Symbology Encoding SWG
Ertz, Olivier (University of Applied Sciences, Western Switzerland, School of Business & Engineering Vaud (HEIG-VD))
Bocher, Erwan (Lab-STICC CNRS UMR 6285)
1. Purpose of the Styles and Symbology Encoding SWG
The purpose of this Standards Working Group is to:
- Maintain the Symbology Conceptual Model: Core Part (SymCore) standard.
- Develop and maintain extensions of the SymCore standard as identified in section 3 (Scope).
- Develop and maintain encodings of the SymCore extensions as identified in section 3 (Scope).
- Maintain the SLD 1.1 and SE 1.1 standards.
2. Business Value Proposition
The existing style and symbology encoding standards for Styled Layer Descriptor (SLD) and Symbology Encoding (SE) laid an important foundation for current portrayal efforts but were limited in scope and did not provide for a family of modular standards to provide a common model with specific extensions and encodings to provide interoperability while accommodating diverse portrayal requirements of multiple domains. SymCore provides the conceptual model to modernize and modularize and was designed to be extended and support multiple encodings. This recharter updates the scope and deliverables of the style and symbology encoding effort.
The recharter of this SWG is intended to define scope and better align activities with the Portrayal DWG, the OGC API – Styles SWG, and the 3D Portrayal Service SWG. Additionally, the modular design of extensions and encodings could inform domain-specific portrayal efforts in other SWGs and DWG. In conjunction with the OGC API – Styles SWG the styles defined will be key components in current OGC web services and emerging OGC APIs.
3. Scope of Work
The Styles and Symbology Encoding SWG will build on the prior work of the SLD and SW SWG, the newly approved conceptual model in SymCore, and the lessons of recent Innovation Program testbeds and pilots to expand and improve specifications for styles and symbology extensions and encodings.
- Conceptual / Information model: The SymCore standard defines the basic components for styles and symbology encoding in the core. As needed, additions to the conceptual model will be addressed as revisions to SymCore or incorporation into extension-specific concepts.
- Modularization: SymCore identifies modular components for portrayal in additional conceptual model parts, extensions to the conceptual model, and encoding of the extensions. Traceability to the conceptual core will be maintained but style and symbology modules will allow for multiple implementations based on the philosophy of one core, many extensions and one conceptual model, many encodings. SymCore defines a basic set of concepts. Additional concepts and conformance classes may be added in additional conceptual model parts or extensions. Metadata requirements will be included as appropriate in each module to properly describe content, including semantics, and enhance access and discovery.
- Extensions: Multiple domain- or function-based extensions of the core may be developed. may be proposed and addressed in revisions to this charter. Extensions will be driven by community interest. Initial development will focus on extension of SymCore for feature symbology for 2-dimensional and 3-dimensional features and on an extension for Gridded Coverage Data. Additional conformance classes will define additional extensions based on the requirements and requirements classes defined in the core. These extensions will meet the needs of use cases that require such capabilities.
- Encodings: Style extension will require encoding language for implementation. Rather than dictate limited encodings, community interest and best practices will determine suitable encodings for the extensions. No encoding will be mandatory. Specific encodings such as JSON and XML will be determined by the SWG for defined extensions or may be adopted as openly published community encodings.
- Reuse: The use of style and symbology resources will be defined to maximize core elements and use existing industry-standards or patterns that are commonly used by developers to improve reuse and reduce requirements for unique components and reduce cost of implementations.
Before finalizing parts of the future versions of the extensions and encodings, completion of the following goals should be verified:
- Working implementations of all capabilities must be available and tested.
- Implementation feedback must be taken into account.
A consequence of this verification process is that the period between the availability of what is considered a mature draft and the finalization of the candidate standard may be longer than in the past. The length of time depends on the availability of evidence about the suitability of the candidate standard based on implementations. Developers will be encouraged as early as possible to implement the draft specification and provide feedback. An aspect of this is public access to drafts from the beginning. To this end, the SWG intends to use a public GitHub repository in the development of this standard. The OGC believes GitHub is the environment many developers are familiar with and use on a daily basis.
3.1 Statement of relationship of planned work to the current OGC standards baseline
These proposed modular standards are intended to be a major component of the OGC standards baseline. Portrayal of geospatial content is critical to adding value to OGC services and API. The proposed enhancements, extensions, and encodings of symbology and styles will define key components for shared visualization of geospatial information.
3.2 What is out of scope?
Standards are important for interoperability. At the same time, it is important that standards only state requirements that are important for a significantly large group of users. Proposals for new SymCore extensions and encoding or change requests to SymCore must identify the user group that will benefit from the proposal and for each proposed conformance class. Otherwise the proposal will be considered out-of-scope.
SymCore provides the core conceptual model for symbology and styles. It envisioned to be extended to provide style and symbology specifications for various domains. Published extensions will support multiple encoding languages which will be documented in separate, modular, multi-part standards. Extensions and profiles not identified as in scope in the previous section will require a revision to the SWG charter prior to commencement of work. Such new work, for example an Advanced Labelling Extension, will be specified as a task order and validated by the Portrayal DWG. If a community has a need to develop a profile, the profile should be specified and governed by that community.
Styles are the basic requirements class defined by the Styles and Symbology Encoding SWG. Styles are also the basic resource described in draft OGC API – Styles specification. The Styles API describes the interface and exchange of styles and will be worked in the OGC API – Styles SWG. Coordination between the SWGs and Portrayal DWG is required.
3.3 Specific Contribution of Existing Work as a Starting Point
The starting point for the work will be the SymCore specification. This charter recognizes the prior work done by the SLD and SE SWG and will be informed by those specifications and the SWG’s experience. The work shall also be based on recommendations found in recent OGC Testbed and Pilot reports.
- [OGC 18-067r2] OGC Symbology Conceptual Model: Core part (SymCore)
- [OGC 05-078r4] OpenGIS Styled Layer Descriptor Profile of the Web Map Service Implementation Specification 1.1
- [OGC 05-077r4] OpenGIS Symbology Encoding Implementation Specification 1.1
- [OGC 19-018] OGC Testbed-15: Open Portrayal Framework Engineering Report
- [OGC 19-010r2] OGC Testbed-15: Styles API Engineering Report
- [OGC 19-023r1] OGC Testbed-15: Encoding and Metadata Conceptual Model for Styles Engineering Report
- [OGC 19-088r2] OGC Vector Tiles Pilot 2: Summary Engineering Report
Each of these documents recommends portrayal, style, and symbology approaches to be considered in symbology conceptual model, extensions, and encodings.
4. Description of deliverables
The following deliverables will result from the work of this SWG. The targeted start date is in October 2020 or once charter is approved. Formal approval of feature extension(s) is envisaged to take place in late 2021.
4.1 Initial Deliverables
The following deliverables will result from the work of this SWG:
- Extension of SymCore for feature symbology for 2-dimensional and 3-dimensional features. The SWG will determine if this should be a single extension or multiple extension.
- Extension of SymCore for Gridded Coverage Data.
- Symbology encoding specification for the published extensions.
- Incorporation of style metadata in all extensions and encodings.
- Identification of at least three prototype implementations of the extensions and encodings — although more would be preferred.
4.2 Additional SWG Tasks
To be completed as SWG takes on new tasks.
5. IPR Policy for this SWG
✓ RAND-Royalty Free. RAND for fee
6. Anticipated Participants
The target audience of Styles and Symbology Encoding standards are implementers and / or users of OGC portrayal services including:
- Geospatial resource providers.
- Developers implementing services.
- Map producers and publishers.
- Producers of data used to create maps.
- Users of geospatial resources.
7. Domain Working Group Endorsement
The Portrayal DWG will review this SWG charter. A statement of endorsement is anticipated at, or soon after, the September 2020 Virtual OGC Members' meeting.
8. Other information about the work of this SWG
Similar or applicable standards work (OGC and elsewhere).
The recharter of this SWG is intended to define scope and better align activities in the Portrayal DWG, the OGC API – Styles SWG, and the 3D Portrayal Service SWG. Additionally, the modular design of extensions and encodings could inform domain-specific portrayal efforts in other SWGs and DWG. In conjunction with the OGC API – Styles SWG the styles defined will be key components in current OGC web services and emerging OGC APIs.
The following standards, documents and presentations may be relevant to the SWG's planned work and may be used as reference points in determining the work needed to provide the functionality anticipated by this committee's deliverables:
- [OGC 15-001r4] OGC 3D Portrayal Service 1.0
- [OGC 09-042] 3D-Symbology Encoding Discussion Paper
- OGC 17-094r1 OGC Portrayal Concept Development Study