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Acquisition Collection File

Last updated: August 12, 2022

Overview

The Acquisition Collection file provides links to STAC item metadata files for each item that is part of the same acquisition. Each STAC Item Metadata file that comes from an acquisition is named {acquisitionID}.json. It is the file path that makes the item name unique.

In an ARD order delivery, a single acquisition will cover multiple grid cells, or quadkeys. In some cases, it may even cross the boundary of two UTM zones. ARD imagery is processed into multiple tiles, based on the quadkey address.

In the example collection file below, the acquisition is divided into three tiles with different quadkey addresses (the example has been truncated for simplification).

./11/031311311232/2021-09-21/104001006D0BB300.json
./11/031311311233/2021-09-21/104001006D0BB300.json
./11/031311311323/2021-09-21/104001006D0BB300.json

Collection file information

This file adheres to the STAC collection specification .

File name: {acquisition ID}_collection.json

File path: bucket/prefix/acquisition_collections/{acquisition ID}_collection.json

File type: GeoJSON (.json)

Collection Fields

The descriptions for STAC fields are taken from the collection specification.

Field Type Description Example
type string The type of the GeoJSON object. The type for a STAC item is "feature". "type": "Collection"
id string The unique identifier for the acquisition: UTM zone/quadkey/acquisition_date/acquisitionID. "id": "11/031311311232/104001006D0BB300"
stac_version string The STAC version for the file schema. "stac_version": "1.0.0"
description string Human-readable description of the file. "description": "104001006D0BB300 ARD Tiles"
links object Provides links to metadata files associated with the acquisition. See "Links object" table below.
extent object Spatial and temporal extents for the acquisition collection. See "Extent object" table below.
license string License type. "license": "proprietary"

The links object provides URLs to metadata files and shows their relationship to the file.

Field Description Example
rel The relationship between the link and the entity it describes. See "relationship" table below. "rel": "collection"
href The URL for the linked file. "href": "../../../acquisition_collections/104001006D0BB300_collection.json"
type The type for the linked file. "type": "application/json"

Relationship types

Type Description Example
item URL to the STAC item file for a tile. "href": "./11/031311311323/2021-09-21/104001006D0BB300.json"
parent URL to the acquisition collection file. "href": "../../../acquisition_collections/104001006D0BB300_collection.json"
root URL to the order collection file. "href": "../../../order_collections/5681790434919305322_root_collection.json"

Note: The "parent" and "root" links go to the same file. Both types are listed for STAC compliance and tool compatibility.

Extent object

The extent object lists the spatial and temporal extents for the collection of items.

Extent Field Description Example
spatial bbox Extents of the acquisition collection. First item is the total extents, additional items are tile extents. "bbox":[[-117.29404086049149, 32.89643160060904, -117.15871490276942, 32.94040782110711],[-117.29404086049149, 32.89643160060904, -117.26563783226379, 32.94040782110711],[-117.26911032701715, 32.89648791009229, -117.21217648743674, 32.93984186226933],[-117.2156193014351, 32.89659148103818, -117.15871490276942, 32.93847442771225]]
temporal interval Date interval extents of the acquisition collection. "interval": [["2021-09-21 18:34:57Z", "2021-09-21 18:34:59Z"]]

Example collection file

{
    "type": "Collection",
    "id": "104001006D0BB300",
    "stac_version": "1.0.0",
    "description": "104001006D0BB300 ARD Tiles",
    "links": [{
        "rel": "root",
        "href": "../order_collections/5681790434919305322_root_collection.json",
        "type": "application/json"
    }, {
        "rel": "parent",
        "href": "../order_collections/5681790434919305322_root_collection.json",
        "type": "application/json"
    }, {
        "rel": "item",
        "href": "../11/031311311232/2021-09-21/104001006D0BB300.json",
        "type": "application/json"
    }, {
        "rel": "item",
        "href": "../11/031311311233/2021-09-21/104001006D0BB300.json",
        "type": "application/json"
    }, {
        "rel": "item",
        "href": "../11/031311311322/2021-09-21/104001006D0BB300.json",
        "type": "application/json"
    }],
    "extent": {
        "spatial": {
            "bbox": [
                [-117.29404086049149, 32.89643160060904, -117.15871490276942, 32.94040782110711]
                [-117.29404086049149, 32.89643160060904, -117.26563783226379, 32.94040782110711],
                [-117.26911032701715, 32.89648791009229, -117.21217648743674, 32.93984186226933],
                [-117.2156193014351, 32.89659148103818, -117.15871490276942, 32.93847442771225]             
            ]
        },
        "temporal": {
            "interval": [
                ["2021-09-21 18:34:57Z", "2021-09-21 18:34:59Z"]
            ]
        }
    },
    "license": "proprietary"
}
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