add single file STAC extension

CHANGELOG.md

@@ -27,6 +27,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - **stac_extensions**: Introduced this field for Items, Catalogs and Collections.
 - Property `summaries` have been added to catalogs and collections.
 - API Transaction extension supports optimistic locking through use of the ETag header.
+- [Single File Catalog extension](extensions/single-file-catalog/README.md) added as a format to have a set of Collections and Items in a single file.
 - [Label extension](extensions/label/README.md) added with additional fields for describing labeled data, such as used for training data or from the output of a classification
 - Timestamp fields added to `Item`: `created` and `updated` to refer to the datetime the metadata file was created or updated.
 - Added Search Metadata API extension which adds fields to a response from a STAC API such as the number of items found and how many were returned.

extensions/README.md

@@ -55,6 +55,7 @@ An extension can add new fields to STAC entities (content extension), or can add
 | [Point Cloud](pointcloud/README.md) (`pc`)                   | Item             | Provides a way to describe point cloud datasets. The point clouds can come from either active or passive sensors, and data is frequently acquired using tools such as LiDAR or coincidence-matched imagery. | *Proposal* |
 | [SAR](sar/README.md) (`sar`)                                 | Item             | Covers synthetic-aperture radar data that represents a snapshot of the earth for a single date and time. | *Proposal* |
 | [Scientific](scientific/README.md) (`sci`)                   | Item +Collection | Scientific metadata is considered to be data that indicate from which publication data originates and how the data itself should be cited or referenced. | *Proposal* |
+| [Single File STAC](single-file-stac/README.md) (-)           | Catalog +Collection +Item | An extension to provide a set of Collections and Items as a single file catalog. | *Proposal* |
 
 ## Third-party / vendor extensions
 

extensions/single-file-stac/README.md

@@ -0,0 +1,32 @@
+# Single File STAC Specification
+
+**Extension [Maturity Classification](../README.md#extension-maturity): Proposal**
+
+An extension to provide a set of Collections and Items as a single file catalog. The single file is a self contained catalog that contains everything that would normally be in a linked set of STAC files. This format is useful to save a portion of a catalog, or when creating a small catalog from derived data that should remain portable. It is most useful for saving the results of a search from a STAC API, as the Items, Collections, and optionally the search parameters are all saved within the single file. Hierarchical links have no meaning in a single file STAC, and so, if present, should be removed when creating a single file catalog.
+
+The Items in the single file catalog should not be merged with the Collection properties (i.e., common properties). The Collections are all included in the file as well, so there is no need to duplicate the common properties for every Item in the catalog.
+
+- [Example](examples/example.json)
+- [JSON Schema](json-schema/schema.json)
+
+## Catalog fields
+
+A Single File STAC is a complete STAC catalog contained in a single file. 
+
+A Single File STAC is an [ItemCollection Object](../../item-spec/itemcollection-spec.md). This GeoJSON FeatureCollection has Features which are Items, but the Collections are still needed.
+
+| Field Name         | Type   | Description                                                  |
+| ------------------ | ------ | ------------------------------------------------------------ |
+| collections | [Collection](../../collection-spec/collection-spec.md#collection-fields)] | An array of Collections that are used by any of the Items in the ItemCollection.
+| search | [Search Object](#search-object) | An optional field containing a search endpoint and parameters used to generate this Single File STAC |
+
+## Search Object
+
+| Field Name         | Type   | Description                                                  |
+| ------------------ | ------ | ------------------------------------------------------------ |
+| endpoint | string | The root endpoint of a STAC API used for this search.
+| parameters | map<string, Object> | A dictionary of all the parameters used for the search |
+
+## Implementations
+
+- [sat-search](https://github.com/sat-utils/sat-search) uses the Single File Catalog to save and load search results.