Add `ItemCollection.to_collection`

[gadomski]

This would be a nice convenience method that would generate the extents, etc from the items in the ItemCollection.

[jsignell]

I think of ItemCollections as more analogous to Catalogs than to Collections. I guess I think that because you can represent items from more than one Collection in an ItemCollection. But I guess from pystac's perspective Collections just inherit from Catalogs so maybe it doesn't matter?

[gadomski]

Yeah, I agree with the general point that not all ItemCollections map to a Collection. However, often they do (e.g. a search result), and creating a "sub-collection" (here's a collection that describes my search results) could be of use to some folks?

[KeynesYouDigIt]

On paper, this makes sense as interesting and I was thinking of taking it on. However, do we have more bites from users on whether or not this would solve an active problem for them?

[gadomski]

Nope! This would be more of a "if you build it they will come" feature.

I do tend to create issues like this one when I'm using pystac and it's ergonomics don't match my expectations, so that's one user I guess 🙂

[jsignell]

I'm taking a crack at this. Considering doing it the other way around and putting a from_items on Collection that way it could take an iterable of items or an ItemCollection. Is there a reason why the other way around would be better you think?

[gadomski]

Is there a reason why the other way around would be better you think?

Nope, makes sense to me, and I feel like we're most of the way there with https://pystac.readthedocs.io/en/stable/api/pystac.html#pystac.Extent.from_items (which I find myself using and then passing to a collection a lot).