The SpatioTemporal Asset Catalog (STAC) specification aims to standardize the way geospatial assets are exposed online and queried. A 'spatiotemporal asset' is any file that represents information about the earth captured in a certain space and time. The initial focus is primarily remotely-sensed imagery (from satellites, but also planes, drones, balloons, etc), but the core is designed to be extensible to SAR, full motion video, point clouds, hyperspectral, LiDAR and derived data like NDVI, Digital Elevation Models, mosaics, etc.
The goal is for all major providers of imagery and other earth observation data to expose their data as spatiotemporal asset catalogs, so that new code doesn't need to be written whenever a new JSON-based REST API comes out that makes its data available in a slightly different way. This will enable standard library components in many languages.
The specification is currently still an early version, with the potential for some major things to change. The core is now fleshed out, so implementors are encouraged to try it out and give feedback. But the goal is to actually be able to act on that feedback, which will mean changes are quite possible.
But efforts will be made to maintain the core fields established in the central JSON Spec. The minimal amount is specified right now, but best practices should emerge with implementation and more will likely be specified.
This repository contains the core specifications, along with examples and JSON schemas for validation. Also included are a few documents that provide more context and plans for the evolution of the specification.
json-spec/ defines a SpatioTemporal Asset Catalog Item, which is a GeoJSON Feature
with additional fields for the time range, links to related entities and resources, including thumbnails. The folder contains
a minimal and expanded samples, validating schemas,
an additional folder of examples and of course the main specification.
static-catalog/ specifies how to utilize Items as ordered files on a web server or object store
like S3, without the need for any dynamic code. These static catalogs are designed to expose the data to be crawled by
other tools.
api-spec/ defines a dynamic API, specified as a yaml file in OpenAPI 2.0 (swagger).
Additional documents include the current roadmap and a complementary how to help document, a list of implementations, and a discussion of the collaboration principles and specification approach.
An important core principle of the STAC design is to embrace best practices of making data available on the web (like HATEOAS and W3C Spatial Data on the Web), and to leverage the reliability of flat files on object stores like AWS S3 and Google Cloud Storage. This leads to putting the 'static catalog' at the core of the STAC spec.
A static catalog is an implementation of the STAC specification that does not respond dynamically to requests - it is simply a set of files on a web server that link to one another in a way that can be crawled. A static catalog can only really be crawled by search engines and active catalogs; it can not respond to queries. But it is incredibly reliable, as there are no moving parts, no clusters or databases to maintain. The goal of STAC is to expose as much asset metadata online as possible, so the static catalog offers a very lower barrier to entry for anyone with geospatial assets to make their data searchable.
A catalog API is a RESTful API that responds to queries (like give me all imagery in Oahu gathered on January 15, 2017). But its structure and responses are designed to mirror the static catalog, so the same client and crawler tools can consume it. It generally indexes data for efficient responses, and aims to be easy for existing API's to implement as a more standard interface for clients to consume. It is specified in OpenAPI 2.0 (swagger), and will move to OpenAPI 3.0 once the codegen tooling is stronger there. An active catalog will often be populated by a static catalog, or at least may have a 'backup' of its fields stored as a cached static catalog.
The SpatioTemporal Asset Metadata specification defines the core fields that all assets must make available for searching in a catalog. Vendors can extend those core fields for the metadata they want to make available, and the community is starting to define shared profiles, with 'earth observation' (satellite imagery) being the first one. This repo contains the STAC Item definition, which is the primary json profile of STAM, so it can evolve with the rest of the STAC spec more easily. The STAM repo retains the abstract definition, and may evolve to contain other profiles.
Anyone building software that catalogs imagery or other geospatial assets is welcome to collaborate. Our goal is to be a collaboration of developers, not architecture astronauts. A number of developers met in person and sprinted on specs and made a number of key decisions.
The best way to contribute is to try to implement the specification and give feedback on what worked well and what could be improved. Currently there are a few major things to still work out, so if you are interested in implementing you should jump on our gitter channel and check in on how ready the spec is and how you can support it. For the next bit of time you'll probably be encouraged to just do what feels best in some areas, so we can capture best practices and standardize.
Any proposed changes to the specification should be done as pull requests. Ideally a proposed change would also update all of the examples, but for now that is not required - the team can validate and update all examples before a release. But it is recommended to update at least a couple examples to reflect the change.