Clarify the implementation of spatial query filter parameters

[damb]

The fdsnws-station spec is not really clear about how to handle requests, when both rectangular spatial query filter parameters and circular spatial query filter parameters are given.

Questions arise, such as:

• Are rectangular and circular query filter parameters mutually exclusive?
• Is data returned matching the resulting union of both the rectangular and circular area? Note, that this approach would require merging the data to be returned since a single station/channel might be part of both areas.

I'm aware, that the implementation of circular query filter parameters is optional.

[chad-earthscope]

It certainly wouldn't hurt to clarify this detail.

At the IRIS DMC we take the first view of the two geographic selection parameters being mutually exclusive, i.e. we do not allow both the rectangular criteria and the distance (circular) criteria in the same query, avoiding the ambiguity.

In my view, if the service API is going to allow multi-geographic region search it needs to be more comprehensive that one rectangle and one circle, which is hardly useful.