Disallow GeometryCollection, reformatting

[m-mohr]

Related Issue(s): #1160

Proposed Changes:

1. Disallow GeometryCollection in Item Spec (as defined in the schema) GeometryCollection not allowed according to Item schema #1160
2. Reformatted the Item Field table to be more lightweight by moving geometry, bbox, and collection descriptions to separate sections. Also, clarified that RFC section 3.1 and 3.2 apply, for Geometry Object and null respectively.

PR Checklist:

• This PR is made against the dev branch (all proposed changes except releases should be against dev, not master).
• This PR has no breaking changes.
• I have added my changes to the CHANGELOG
  or a CHANGELOG entry is not required.
• This PR affects the STAC API spec,
  and I have opened issue/PR #XXX to track the change.

[emmanuelmathot]

This change in the schema would enforce it at validation

diff --git a/item-spec/json-schema/item.json b/item-spec/json-schema/item.json
index ede4d62a..61475e1b 100644
--- a/item-spec/json-schema/item.json
+++ b/item-spec/json-schema/item.json
@@ -15,6 +15,30 @@
         {
           "$ref": "https://geojson.org/schema/Feature.json"
         },
+        {
+          "$comment": "Disallow GeometryCollection",
+          "not": {
+            "type": "object",
+            "required": [
+              "geometry"
+            ],
+            "properties": {
+              "geometry": {
+                "type": "object",
+                "required": [
+                  "type"
+                ],
+                "properties": {
+                  "type": {
+                    "enum": [
+                      "GeometryCollection"
+                    ]
+                  }
+                }
+              }
+            }
+          }
+        },
         {
           "oneOf": [
             {
@@ -260,4 +284,4 @@
       ]
     }
   }
-}
+}
\ No newline at end of file

[m-mohr]

I thought we were already enforcing it in validation, I'll check, thanks.

See : #1160 (comment)

[emmanuelmathot]

yes right, with the coordinates fields

[m-mohr]

This line enforces it, because it doesn't contain GeometryCollection:
https://github.com/radiantearth/stac-spec/blob/master/item-spec/json-schema/item.json#L47

If that's fine for you, you could approve it @emmanuelmathot

[m-mohr]

@gadomski @emmanuelmathot Ready for another review.