Implement crs and geometrycolumn fallbacks via DataAPI

Project.toml

@@ -4,10 +4,12 @@ authors = ["JuliaGeo and contributors"]
 version = "1.3.6"
 
 [deps]
+DataAPI = "9a962f9c-6df0-11e9-0e5d-c546b8b5ee8a"
 Extents = "411431e0-e8b7-467b-b5e0-f676ba4f2910"
 GeoFormatTypes = "68eda718-8dee-11e9-39e7-89f7f65f511f"
 
 [compat]
+DataAPI = "1"
 Extents = "0.1.1"
 GeoFormatTypes = "0.4"
 julia = "1"

src/GeoInterface.jl

@@ -3,6 +3,7 @@ module GeoInterface
 using Extents: Extents, Extent
 using GeoFormatTypes: CoordinateReferenceSystemFormat
 using Base.Iterators: flatten
+import DataAPI
 
 export testgeometry, isgeometry, trait, geomtrait, ncoord, getcoord, ngeom, getgeom
 

src/fallbacks.jl

@@ -95,8 +95,17 @@
 issimple(t::AbstractMultiCurveTrait, geom) = all(issimple.(getgeom(t, geom)))
 isclosed(t::AbstractMultiCurveTrait, geom) = all(isclosed.(getgeom(t, geom)))
 
-crs(::Nothing, geom) = nothing
-crs(::AbstractTrait, geom) = nothing
+crs(::Nothing, geom) = _get_dataapi_metadata(geom, "GEOINTERFACE:crs", nothing)
+crs(::AbstractTrait, geom) = _get_dataapi_metadata(geom, "GEOINTERFACE:crs", nothing)
+
+function _get_dataapi_metadata(geom::GeomType, key, default) where GeomType
+ if DataAPI.metadatasupport(GeomType).read
+ if key in DataAPI.metadatakeys(geom)
+ return DataAPI.metadata(geom, key; style = false)
+ end
+ end
+ return default
+end
 
 # FeatureCollection
 getfeature(t::AbstractFeatureCollectionTrait, fc) = (getfeature(t, fc, i) for i in 1:nfeature(t, fc))

src/interface.jl

@@ -44,7 +44,7 @@ isfeaturecollection(::Type{T}) where {T} = false
 Retrieve the geometrycolumn(s) of `featurecollection`; the fields (or columns in a table)
 which contain geometries that support GeoInterface.
 """
-geometrycolumns(featurecollection) = (:geometry,)
+geometrycolumns(featurecollection) = _get_dataapi_metadata(featurecollection, "GEOINTERFACE:geometrycolumns", (:geometry,))
 
 """
  GeoInterface.geometry(feat) => geom