Clarification on MultiPolygon, MultiPolygonSeries, and possibly MultiPoint Coverages

[murithigeo]

According to the Covjson Playground, each polygon in a MultiPolygon has a different associated value in linked ranges. For instance, in the first Polygon value, the temperature value is different from the subsequent polygon value.

Wouldn't it make sense that geographic features represented by a MultiPolygon have the same associated value?

[jonblower]

This is a good point, and I think you have found an inconsistency. The Polygon domain type is defined as having a single polygon to define its domain, but there are two possible meanings of "MultiPolygon":

1. A single domain element that is made up of multiple discontiguous polygons (like the land area of the USA)
2. A domain that contains a number of polygons, each of which has its own range value.

The CovJSON spec is not completely clear, but implies that the second one is correct (because the length of the range in the example is the same as the length of the z axis, implying that the polygons are considered part of the same domain element).

But, as you say, the Playground treats the polygons as different domain elements in the MultiPolygon example.

Assuming that the spec is the source of truth, this means:

1. The playground example should be corrected, and
2. We probably need a way to accommodate the second use case above

@murithigeo does the above make sense to you?

[murithigeo]

I understand the implication. Given the spec also uses the first meaning, then I think it would make sense to use the first meaning until the alternate case is accomodated

[jonblower]

Yes, I agree. The second use case could be accommodated through a CoverageCollection (like the example of the Point Collection in the Playground).

As the title of this issue suggests, I think we may also have an issue with the MultiPoint domain type. We probably need to check what the schema and validator tools do too.

I'm labelling this for the next bugfix release

[chris-little]

@jonblower @murithigeo I am happy with the above analysis. Are there any volunteers for fixing:

1. CovJSON playground
2. Disambiguating the OGC Spec
3. Clarify and fixing the schemas and tests?