Friday, June 1, 2018

Where We Are with Feature Styling and Portrayal

The GeoPackage SWG is very interested in solving the portrayal issue - how to encode style/symbology for GeoPackage feature data so that it can be portrayed or rendered in a client application. It is the #1 thing I hear about and I am committed to getting there. While proprietary solutions exist, we want something that will be interoperable. It is just taking a while and we need to be patient because there are a lot of moving parts. 

SWG members have asked for three things in a candidate solution:
  1. SQL table-based (since GeoPackage is an SQLite encoding)
  2. Consistent across the OGC baseline (so that implementers can build a single basic approach for the baseline, as opposed to a GeoPackage-specific implementation)
  3. Loose coupling of the features and their styles (unlike KML, for example)
OGC hasn't nailed down a solution for #1 and #2 yet, but it is in progress. The Styled Layer Descriptor SWG has awoken from its decade-long slumber and is in the process of producing a v2 which is basically a total rewrite. In this version, they will implement a core and extensions model and support multiple encodings, resolving two major gaps in the original version. I was one of the contributors to a document called the Portrayal Concept Development Study Engineering Report which discusses these concepts in great detail. I hope for this document to be published in the next month or so. This will also be a hot topic at the OGC Technical Committee meetings in Ft. Collins next week.

To address #3, I believe the way to go is to harmonize GeoPackage and OWS Context so that the two work seamlessly with each other. I have written a discussion paper on the topic. I will present this paper to the GeoPackage SWG next week and if all goes well, it will be published by OGC later this month. I believe the concept is ready to go except for the style encoding. Once that is resolved, we should be able to standardize this pretty quickly. By the way, as far as I know, this would be the first time OGC adopts a standard that is an extension for two different standards simultaneously.

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