Projection Extension

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
      - Instrument extension, adds fields: `platform`, `instruments`, `constellation` (all moved from EO and SAR extensions), and `mission`
      - Data Cube extension can be used in Collections, added new field `description`
      - Added `description` and `roles` fields to the Asset in the [Asset Extension](extensions/asset/README.md)
+     - Projection Extension to describe Items with Assets that have an associated geospatial projection.
 - STAC API:
      - Added the [Item and Collection API Version extension](api-spec/extensions/version/README.md) to support versioning in the API specification
      - Run `npm run serve` or `npm run serve-ext` to quickly render development versions of the OpenAPI spec in the browser.
@@ -24,7 +25,6 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Added attribute `roles` to Item assets (also Asset definitions extension), to be used similarly to Link `rel`.
 - Updated API yaml to clarify bbox filter should be implemented without brackets. Example: `bbox=160.6,-55.95,-170,-25.89`
 - Collection `summaries` merge array fields now.
-
 - Extensions:
     - [datetime-range extension](extensions/datetime-range/README.md): Removed extension prefix from example and schema
     - Data Cube extension: Changed allowed formats (removed PROJ string, added PROJJSON / WKT2) for reference systems
@@ -51,6 +51,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - `license` field doesn't allow SPDX expressions any longer. Use `various` and links instead.
 - STAC API:
     - Removed "next" from the search metadata and query parameter, added POST body and headers to the links for paging support
+- Removed from EO extension field `eo:epsg` in favor of `proj:epsg`
 
 ### Fixed
 

collection-spec/collection-spec.md

@@ -151,7 +151,7 @@ Implementors are free to add other derived statistical values to the object, for
 
 STAC Collections which don't link to any Item are called **standalone Collections**.
 To describe them with more fields than the Collection fields has to offer, it is allowed to re-use the metadata fields defined by content extensions for Items in the `summaries` field.
-This makes much sense for fields such as `platform` or `eo:epsg`, which are often the same for a whole collection, but doesn't make much sense for `eo:cloud_cover`, which usually varies heavily across a Collection.
+This makes much sense for fields such as `platform` or `proj:epsg`, which are often the same for a whole collection, but doesn't make much sense for `eo:cloud_cover`, which usually varies heavily across a Collection.
 The data provider is free to decide, which fields are reasoable to be used.
 
 ## Extensions

collection-spec/examples/sentinel2.json

@@ -62,7 +62,7 @@
     },
     "sci:citation": ["Copernicus Sentinel data [Year]"],
     "eo:gsd": [10,30,60],
-    "eo:epsg": [32601,32602,32603,32604,32605,32606,32607,32608,32609,32610,32611,32612,32613,32614,32615,32616,32617,32618,32619,32620,32621,32622,32623,32624,32625,32626,32627,32628,32629,32630,32631,32632,32633,32634,32635,32636,32637,32638,32639,32640,32641,32642,32643,32644,32645,32646,32647,32648,32649,32650,32651,32652,32653,32654,32655,32656,32657,32658,32659,32660],
+    "proj:epsg": [32601,32602,32603,32604,32605,32606,32607,32608,32609,32610,32611,32612,32613,32614,32615,32616,32617,32618,32619,32620,32621,32622,32623,32624,32625,32626,32627,32628,32629,32630,32631,32632,32633,32634,32635,32636,32637,32638,32639,32640,32641,32642,32643,32644,32645,32646,32647,32648,32649,32650,32651,32652,32653,32654,32655,32656,32657,32658,32659,32660],
     "eo:bands": [
       {
         "name": "B1",

extensions/README.md

@@ -56,6 +56,7 @@ An extension can add new fields to STAC entities (content extension), or can add
 | [Instrument](instrument/README.md) (-)                       | Item             | Adds metadata specifying a platform and instrument used in a data collection mission. | *Proposal* |
 | [Label](label/README.md) (`label`)                           | Item             | Items that relate labeled AOIs with source imagery | *Proposal* |
 | [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* |
+| [Projection](projection/README.md) (`proj`)                  | Item             | Provides a way to describe items whose assets are in a geospatial projection. | *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* |
 | [Satellite](sat/README.md) (`sat`)                           | Item             | Satellite related metadata for data collected from satellites. | *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* |

extensions/datacube/examples/example-collection.json

@@ -51,7 +51,7 @@
     "eo:platform": ["sentinel-2a","sentinel-2b"],
     "eo:constellation": ["sentinel-2"],
     "eo:instrument": ["msi"],
-    "eo:epsg": [3857],
+    "proj:epsg": [3857],
     "eo:bands": [
       [
         {

extensions/eo/README.md

@@ -29,7 +29,6 @@ If the data has been collected by a satellite, it is strongly recommended to use
 | ---------------- | ------------------------ | ----------- |
 | eo:gsd           | number                   | **REQUIRED.** Ground Sample Distance at the sensor. |
 | eo:bands         | [[Band Object](#band-object)] | **REQUIRED.** This is a list of the available bands where each item is a [Band Object](#band-object). |
-| eo:epsg          | integer\|null            | [EPSG code](http://www.epsg-registry.org/) of the datasource, `null` if no EPSG code. |
 | eo:cloud_cover   | number                   | Estimate of cloud cover as a percentage (0-100) of the entire scene. If not available the field should not be provided. |
 
 **eo:gsd** is the nominal Ground Sample Distance for the data, as measured in meters on the ground. There are many
@@ -43,12 +42,6 @@ PlanetScope Ortho Tile Product has an `eo:gsd` of 3.7 (or 4 if rounding), even t
 3.125.   For example, one might choose for WorldView-2 the 
 Multispectral 20° off-nadir value of 2.07 and for WorldView-3 the Multispectral 20° off-nadir value of 1.38.
 
-**eo:epsg** - A Coordinate Reference System (CRS) is the native reference system (sometimes called a
-'projection') used by the data, and can usually be referenced using an [EPSG code](http://epsg.io).
-If the data does not have a CRS, such as in the case of non-rectified imagery with Ground Control
-Points, eo:epsg should be set to null. It should also be set to null if a CRS exists, but for which
-there is no valid EPSG code.
-
 ### Band Object
 
 | Field Name          | Type   | Description                                                  |

extensions/eo/examples/example-landsat8.json

@@ -42,16 +42,16 @@
         ]
     },
     "properties": {
+        "platform": "landsat-8",
+        "instrument": ["oli", "tirs"],
         "datetime": "2018-10-01T01:08:32.033Z",
-        "eo:cloud_cover": 78,
         "sat:sun_azimuth_angle": 168.8989761,
         "sat:sun_elevation_angle": 26.32596431,
+        "sat:off_nadir_angle": 0,
         "landsat:path": 107,
         "landsat:row": 18,
         "eo:gsd": 30,
-        "platform": "landsat-8",
-        "instrument": ["oli", "tirs"],
-        "sat:off_nadir_angle": 0,
+        "eo:cloud_cover": 78,
         "eo:bands": [
             {
                 "name": "B1",

extensions/eo/json-schema/schema.json

@@ -62,13 +62,6 @@
                 }
               }
             },
-            "eo:epsg": {
-              "title": "EPSG code",
-              "type": [
-                "integer",
-                "null"
-              ]
-            },
             "eo:cloud_cover": {
               "title": "Cloud Cover",
               "type": "number",

extensions/projection/README.md

@@ -0,0 +1,79 @@
+# Projection Extension Specification (`proj`)
+
+**Extension [Maturity Classification](../README.md#extension-maturity): Proposal**
+
+This document explains the fields of the STAC Projection (`proj`) Extension to a STAC Item. Here `proj` is short
+for "projection", and not a reference to the use of the PROJ/PROJ4 formats.
+
+The field names defined herein should be added as fields in the Item Properties object. 
+
+When specified on an Item, the values are assumed to apply to all Assets in that Item.  For example, an Item may have 
+several related Assets each representing a band or layer for the Item, and which typically all use the same CRS, 
+e.g. a UTM Zone.  However, there may also be assets intended for display, like a preview image or thumbnail, that have 
+been reprojected to a different CRS, e.g., Web Mercator, to better accommodate that use case.  This case of differing 
+projections per Asset is not currently handled by this extension.
+
+## Examples
+- [Example Landsat8](examples/example-landsat8.json)
+
+## Schema
+- [JSON Schema](json-schema/schema.json)
+
+## Item Properties fields
+
+| Field Name       | Type                     | Description |
+| ---------------- | ------------------------ | ----------- |
+| proj:epsg        | integer\|null   | **Required** [EPSG code](http://www.epsg-registry.org/) of the datasource |
+| proj:proj4       | string \|null   | PROJ4 string representing the Coordinate Reference System (CRS) that the `proj:geometry` and `proj:bbox` fields represent |
+| proj:wkt2        | string \|null   | WKT2 string representing the Coordinate Reference System (CRS) that the `proj:geometry` and `proj:bbox` fields represent |
+| proj:projjson    | [PROJJSON Object](https://proj.org/usage/projjson.html) \|null   | PROJJSON object representing the Coordinate Reference System (CRS) that the `proj:geometry` and `proj:bbox` fields represent |
+| proj:geometry    | [Polygon Object](https://geojson.org/schema/Polygon.json)  | Defines the footprint of this Item. |
+| proj:bbox        | [number]        | Bounding box of the Item in the asset CRS in 2 or 3 dimensions. |
+| proj:centroid    | Centroid Object | Coordinates representing the centroid of the Item in the asset CRS |
+
+**proj:epsg** - A Coordinate Reference System (CRS) is the data reference system (sometimes called a
+'projection') used by the asset data, and can usually be referenced using an [EPSG code](http://epsg.io).
+If the asset data does not have a CRS, such as in the case of non-rectified imagery with Ground Control
+Points, `proj:epsg` should be set to null. It should also be set to null if a CRS exists, but for which
+there is no valid EPSG code.
+
+**proj:proj4** - A Coordinate Reference System (CRS) is the data reference system (sometimes called a
+'projection') used by the asset data. This value is a PROJ4 string.
+If the data does not have a CRS, such as in the case of non-rectified imagery with Ground Control
+Points, `proj:proj4` should be set to null. It should also be set to null if a CRS exists, but for which
+a PROJ4 string does not exist.
+
+**proj:wkt2** - A Coordinate Reference System (CRS) is the data reference system (sometimes called a
+'projection') used by the asset data. This value is a WKT2 string.
+If the data does not have a CRS, such as in the case of non-rectified imagery with Ground Control
+Points, proj:wkt2 should be set to null. It should also be set to null if a CRS exists, but for which
+a WKT2 string does not exist.
+
+**proj:projjson** - A Coordinate Reference System (CRS) is the data reference system (sometimes called a
+'projection') used by the asset data. This value is a [PROJJSON](https://proj.org/usage/projjson.html) object.
+If the data does not have a CRS, such as in the case of non-rectified imagery with Ground Control
+Points, proj:projjson should be set to null. It should also be set to null if a CRS exists, but for which
+a PROJJSON string does not exist. The schema for this object can be found [here](https://proj.org/schemas/v0.1/projjson.schema.json).
+
+**proj:geometry** - A Polygon object representing the footprint of this item, formatted according the Polygon 
+object format specified in [RFC 7946, sections 3.1.6](https://tools.ietf.org/html/rfc7946), except not necessarily 
+in EPSG:4326 as required by RFC7946.  Specified based on the `proj:proj4` field (not necessarily EPSG:4326). 
+Ideally, this will be represented by a Polygon with five coordinates, as the item in the asset data CRS should be 
+a square aligned to the original CRS grid. 
+
+**proj:bbox** - Bounding box of the assets represented by this item in the asset data CRS. Specified as 4 or 6 
+coordinates based on the CRS defined in the `proj:epsg` and `proj:proj4` fields.  First two numbers are coordinates 
+of the lower left corner, followed by coordinates of upper right corner, , e.g., \[west, south, east, north], 
+\[xmin, ymin, xmax, ymax], \[left, down, right, up], or \[west, south, lowest, east, north, highest]. The length of the array must be 2*n where n is the number of dimensions. The array contains all axes of the southwesterly most extent followed by all axes of the northeasterly most extent specified in Longitude/Latitude or Longitude/Latitude/Elevation based on [WGS 84](http://www.opengis.net/def/crs/OGC/1.3/CRS84). When using 3D geometries, the elevation of the southwesterly most extent is the minimum elevation in meters and the elevation of the northeasterly most extent is the maximum in meters.
+
+**proj:centroid** - Coordinates representing the centroid of the item in the asset data CRS.  Coordinates are 
+defined in latitude and longitude, even if the data coordinate system does not use lat/long.
+
+## Centroid Object
+
+This object represents the centroid of an item's geometry.
+
+| Field Name          | Type   | Description                                                  |
+| ------------------- | ------ | ------------------------------------------------------------ |
+| lat                 | number | The latitude of the centroid.  |
+| lon                 | number | The longitude of the centroid. |