How to implement filtering using point + range

[lvdbrink]

I couldn't find this in the spec (part 1 or 3) or in an earlier issue, apologies if I overlooked something.

Is there a way to implement a filter where the client sends a POINT geometry in the request and the server returns all features within a certain range of this POINT? The range could be e.g. a kilometer, in the case I'm asking about this is fixed on the server, the client cannot ask for a specific range.

It seems to me this is a common thing for users to want. Quoting the SDW-BP:

Support queries for Spatial Things based on user needs. For spatial data, typical needs that should be considered are neighborhood searches (e.g., "what is near me?" or "what is near this Spatial Thing?")

[cportele]

There is currently no standardized way for such a query. The server would have to provide a CQL2 buffer function.

Of course, the client could also create a polygon that approximates a circle, but this wouldn't work for the use case.

If the range is fixed, a specific function that just takes a point might be the right approach anyway. Or maybe a custom query parameter.

We restricted CQL2 to the spatial predicates in the first version, functions that compute geometries will likely be added in the future in a new conformance class, also to support non-boolean expressions.

[cportele]

Meeting 2023-04-24: This could be implemented in an extension or in a future version.

[jerstlouis]

A distance() function that returns the distance between two geometries (including a POINT() supplied as part of the CQL2 expression) could be another approach.
Unlike buffer(), this approach does not require instantiating a new geometry, so depending on optimizations, it might perform slightly better.

In symbolization, the resulting value could also be used to illustrate this distance with a gradient / colormap.