Clarify/fix proj:epsg requirement (#15)

* Add more examples, clarify/fix `proj:epsg` requirement #7, align repo with template

* Don't require proj:epsg as discussed in the STAC meeting

* Clarification

* Recommendation around thumbnails

* Update README.md

Co-authored-by: Pete Gadomski <[email protected]>

---------

Co-authored-by: Pete Gadomski <[email protected]>

Author: 2 people

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- `proj:epsg` is not required in Item properties anymore. `proj:epsg` is recommended now, but not required in any scope.
 - Updated the PROJJSON schema to v0.5
 
 ### Deprecated

README.md

@@ -72,7 +72,7 @@ A Coordinate Reference System (CRS) is the data reference system (sometimes call
 [EPSG code](https://en.wikipedia.org/wiki/EPSG_Geodetic_Parameter_Dataset).
 A great tool to help find EPSG codes is [epsg.io](http://epsg.io/).
 
-This field must be set to `null` in the following cases:
+This field SHOULD be set to `null` in the following cases:
 - The asset data does not have a CRS, such as in the case of non-rectified imagery with Ground Control Points.
 - A CRS exists, but there is no valid EPSG code for it. In this case, the CRS should be provided in `proj:wkt2` and/or `proj:projjson`.
   Clients can prefer to take either, although there may be discrepancies in how each might be interpreted.
@@ -82,7 +82,7 @@ This field must be set to `null` in the following cases:
 A Coordinate Reference System (CRS) is the data reference system (sometimes called a 'projection')
 used by the asset data. This value is a [WKT2](http://docs.opengeospatial.org/is/12-063r5/12-063r5.html) string.
 
-This field should be set to `null` in the following cases:
+This field SHOULD be set to `null` in the following cases:
 - The asset data does not have a CRS, such as in the case of non-rectified imagery with Ground Control Points.
 - A CRS exists, but there is no valid WKT2 string for it.
 
@@ -92,7 +92,7 @@ A Coordinate Reference System (CRS) is the data reference system (sometimes call
 used by the asset data. This value is a [PROJJSON](https://proj.org/specifications/projjson.html) object, 
 see the [JSON Schema](https://proj.org/schemas/v0.5/projjson.schema.json) for details.
 
-This field should be set to `null` in the following cases:
+This field SHOULD be set to `null` in the following cases:
 - The asset data does not have a CRS, such as in the case of non-rectified imagery with Ground Control Points.
 - A CRS exists, but there is no valid WKT2 string for it.
 

examples/assets.json

@@ -43,7 +43,7 @@
     "created": "2020-12-12T01:48:13.725Z",
     "updated": "2020-12-12T01:48:13.725Z",
     "platform": "cool_sat2",
-    "proj:epsg": null,
+    "proj:epsg": 32659,
     "instruments": [
       "cool_sensor_v1"
     ]
@@ -84,6 +84,11 @@
     "thumbnail": {
       "href": "https://storage.googleapis.com/open-cogs/stac-examples/20201211_223832_CS2.jpg",
       "title": "Thumbnail",
+      "proj:epsg": null,
+      "proj:shape": [
+        800,
+        800
+      ],
       "type": "image/png",
       "roles": [
         "thumbnail"

json-schema/schema.json

@@ -23,17 +23,7 @@
               "const": "Feature"
             },
             "properties": {
-              "allOf": [
-                {
-                  "$comment": "Require fields here for item properties.",
-                  "required": [
-                    "proj:code"
-                  ]
-                },
-                {
-                  "$ref": "#/definitions/fields"
-                }
-              ]
+              "$ref": "#/definitions/fields"
             },
             "assets": {
               "type": "object",