STAC Basics

The key parts of a Spatio-Temporal Asset Catalog (STAC) are Items, Catalogs, and Collections.

1. Item: Usually one image. Has an href where you can find this image.

An Item represents a single spatiotemporal asset as GeoJSON so it can be searched.

Also-

An Item is a GeoJSON Feature augmented with foreign members relevant to a STAC object.

The item has “assets” which are the links to the actual images. The item can have multiple assets (e.g. a full-res image, a thumbnail, and a metadata XML file.)

1. Catalog A group of Items, or other Catalogs. Analogy: a folder on your filesystem. Can also group together collections (i.e. you can have a Catalog that just points to other Catalogs, or other Collections).

2. Collection Like a Catalog (shares much of the same metadata), but goes further and has things like

   • a license
   • temporal / spatial extent
   • provider
   • summaries
   • keywords Each item contained in a collection links to the collection to make it easy to find the relevant metadata.

The Diagram is probably too complex for a starting point, but shows all possible links:

References

1. https://github.com/radiantearth/stac-spec/blob/v1.0.0/overview.md
2. https://github.com/radiantearth/stac-spec/blob/v1.0.0/item-spec/item-spec.md