projection extension scope in Collection?

[emmanuelmathot]

Context

• The scope of the extensions defines where the extensions fields can be found.
• Implicitly, all item fields could be summarized in collection (Assumption)

Questions

Does the scope define a strict limitation of where the field can be found?

• If yes, then the projection extension is limited to Item and thus proj:espg should not be summarized as in the example in https://github.com/radiantearth/stac-spec/blob/master/examples/collection-only/collection.json
• If no, is it necessary to set the scope to collection in the extension definition?

Clarification is needed for the implementation of the helpers methods in the libraries implementing STAC spec and extensions.

[m-mohr]

It's "no". This is an oversight on our side, we should've added the scope Collection here. I added it now, which is just a bug fix as the schemas already support validating in collection assets and item asset definitions.

Validating the summaries is a weak point though. Due to the different structures the summaries have (array and stats object), the fields can't be validated (yet?). So the stac_extensions flag doesn't really apply for summaries and extensions, but only really applies to assets / item_assets in Collections.

[m-mohr]

See also radiantearth/stac-spec#1077 for some more context and a change I'd like to propose.

[emmanuelmathot]

yes indeed, I am reviewing radiantearth/stac-spec#1078 that helps me to understand how it is applied.