Geometry validation error on Item spec

[g-demarco]

Hi, I'm getting an error using the item schema (https://github.com/radiantearth/stac-spec/blob/master/item-spec/json-schema/item.json) I'm trying to create an item with a geometry equal to null, but with a populated bbox. Looking at the definition it should work, but i'm getting back this error:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python2.7/site-packages/jsonschema/validators.py", line 353, in validate
    raise error
ValidationError: {u'assets': {}, u'links': [], u'geometry': None, u'properties': {u'datetime': u'+00:00'}, u'stac_version': u'1.0.0', u'bbox': [1, 1, 1, 1], u'type': u'Feature', u'id': u'q12e'} is not valid under any of the given schemas

Failed validating u'oneOf' in schema[u'allOf'][0][u'allOf'][1]:
{
   "u""oneOf":[
      {
         "u""properties":{
            "u""bbox":{
               "u""items":{
                  "u""type":"u""number"
               },
               "u""oneOf":[
                  {
                     "u""maxItems":4,
                     "u""minItems":4
                  },
                  {
                     "u""maxItems":6,
                     "u""minItems":6
                  }
               ],
               "u""type":"u""array"
            },
            "u""geometry":{
               "u""$ref":"u""https://geojson.org/schema/Geometry.json"
            }
         },
         "u""required":[
            "u""geometry",
            "u""bbox"
         ],
         "u""type":"u""object"
      },
      {
         "u""properties":{
            "u""bbox":{
               "u""not":{

               }
            },
            "u""geometry":{
               "u""type":"u""null"
            }
         },
         "u""required":[
            "u""geometry"
         ],
         "u""type":"u""object"
      }
   ]
}

On instance:
    {
           u'assets': {},
           u'bbox': [1, 1, 1, 1],
           u'geometry': None,
           u'id': u'q12e',
           u'links': [],
           u'properties': {u'datetime': u'+00:00'},
           u'stac_version': u'1.0.0',
           u'type': u'Feature'
}

I'm using a Draft7 compliant validator (https://github.com/Julian/jsonschema)

Any hint for how to address this problem?

[emmanuelmathot]

Indeed, the spec says

bbox REQUIRED if geometry is not null

but it is missing a constraint that it should not be specified if geometry is null. IMO, an item with a bbox has necessarily a geometry that is at least the polygon represented by the bbox.

[m-mohr]

Yep, I agree. I believe the intention was that if you have a bbox, you must also provide a geometry with at least the extent of the bounding box. The JSON Schema seems to already follow this, but we'll likely need to clarify this in the written spec. Or do people prefer to fix the JSON Schema? @cholmes

Anyway, to "solve" the issue in 1.0.0, you'd need to provide a geometry that is equivalent to the bbox.

[g-demarco]

Yes @m-mohr, the problem was found "explorating" the schema, it is clear that with a full geometry everything works fine. The problem should be just the mismatch between the schema and the specification.

Also, the clause:

"bbox": { 
    "not": {}
}

doesn't really seem to be working, but I don't know if it is a problem with the validator or something else.

[m-mohr]

@matthewhanson To do the Markdown PR, @m-mohr to do the JSON Schema.

If there is a bbox you must have a geometry. We couldn't find a use case for having a bbox and not a geometry as you could always provide the bbox also as geometry. If you have use cases, please let us know.

[TomAugspurger]

The JSON Schema seems to already follow this, but we'll likely need to clarify this in the written spec. Or do people prefer to fix the JSON Schema?

I agree that updating the written spec to state that bbox should be non-null if and only if geometry is non-null (otherwise, just set the geometry to the bbox).

It seems to be like the JSON schema is already enforcing this.

[jsignell]

It seems like the written spec is correct on the dev branch: https://github.com/radiantearth/stac-spec/blob/dev/item-spec/item-spec.md

[TomAugspurger]

Good catch, thanks!

[m-mohr]

So we can close this? :-)

[m-mohr]

Just testing this:

Geometry	BBox	Result
Polygon	missing	Fails
Polygon	null	Fails
Polygon	BBox	Valid
null	missing	Valid
null	null	Fails
null	BBox	Fails

The results is compliant to https://github.com/radiantearth/stac-spec/blob/dev/item-spec/item-spec.md