Task - Generate simplified geometry on-the-fly for returned objets - study

[nrevelant]

• a geometry simplification capability has to be planned for the returned objects in order to reduce response size

• are concerned the responses with one feature or several features:

  • GET on a feature : /collections/{id}/items/{fid}
  • GET on a collection : /collections/{id}/items
  • GET on a collection with filter(s) ? : /collections/{id}/items

• An URL parameter representing the simplification level (Level Of Detail) needs to be implemented :

  • -> name : max-allowable-offset according to https://github.com/opengeospatial/ogcapi-features/issues/654
  • -> The value is in the units of the response coordinate reference system. (degree for 4326 SRID or meter for 2154 for example)
  • target function at postGIS level: geometry ST_Simplify(geometry geomA, float tolerance, boolean preserveCollapsed);

• Are excluded from this functionality all POINT and MULTIPOINT features

• Are concerned all the LINE / MULTILINE and POLYGON / MULTIPOLYGON features

OGC Feature discussions : https://github.com/opengeospatial/ogcapi-features/projects/13?card_filter_query=label%3A%22part+n%3A+geometry+simplification%22 https://github.com/opengeospatial/ogcapi-features/issues/654

[benoitdm-oslandia]

Please check Postgis doc

[nrevelant]

It seems interesting to mention that The orb package is currently used by pg_featureserv. And it seems interesting to mention that this component provides a simplification function like postgis does : https://github.com/paulmach/orb/tree/master/simplify#dp In the case we face performance issues or overload on the database, this could represent a solution.