add convert methods

Author: rafaqz

src/geointerface.jl

@@ -12,9 +12,17 @@ GI.geomtrait(g::MultiLineString) = GI.MultiLineStringTrait()
 GI.geomtrait(g::MultiPolygon) = GI.MultiPolygonTrait()
 GI.geomtrait(g::GeometryCollection) = GI.GeometryCollectionTrait()
 
+GI.traittype(::Val{:GeoJSON}, ::GI.PointTrait) = Point
+GI.traittype(::Val{:GeoJSON}, ::GI.LineStringTrait) = LineString
+GI.traittype(::Val{:GeoJSON}, ::GI.PolygonTrait) = Polygon
+GI.traittype(::Val{:GeoJSON}, ::GI.MultiLineStringTrait) = MultiLineString
+GI.traittype(::Val{:GeoJSON}, ::GI.MultiPolygonTrait) = MultiPolygon
+GI.traittype(::Val{:GeoJSON}, ::GI.GeometryCollectionTrait) = GeometryCollection
+
 # we have to make use of the GI fallbacks that call geomtrait on the input
 GI.ncoord(::GI.PointTrait, g::Point) = length(g)
 GI.getcoord(::GI.PointTrait, g::Point, i::Int) = g[i]
+GI.convert(::Type{<:Point}, ::GI.PointTrait, geom) = Point(; coordinates=collect(GI.getcoord(geom)))
 
 GI.ncoord(::GI.LineStringTrait, g::LineString) = length(first(g))
 GI.ngeom(::GI.LineStringTrait, g::LineString) = length(g)
@@ -23,42 +31,65 @@ GI.getpoint(::GI.LineStringTrait, g::LineString, i::Int) = Point(coordinates = g
 # TODO what to return for length 0 and 1?
 # TODO should this be an approximate equals for floating point?
 GI.isclosed(::GI.LineStringTrait, g::LineString) = first(g) == last(g)
+GI.convert(::Type{<:LineString}, ::GI.LineStringTrait, geom) =
+    LineString(; coordinates=coordinates(geom))
 
 GI.ngeom(::GI.PolygonTrait, g::Polygon) = length(g)
 GI.getgeom(::GI.PolygonTrait, g::Polygon, i::Integer) = LineString(coordinates = g[i])
 GI.ncoord(::GI.PolygonTrait, g::Polygon) = length(first(first(g)))
 GI.getexterior(::GI.PolygonTrait, g::Polygon) = LineString(coordinates = first(g))
 GI.nhole(::GI.PolygonTrait, g::Polygon) = length(g) - 1
 GI.gethole(::GI.PolygonTrait, g::Polygon, i::Int) = LineString(coordinates = g[i+1])
+GI.convert(::Type{<:Polygon}, ::GI.PolygonTrait, geom) =
+    Polygon(; coordinates=coordinates(geom))
 
 GI.ncoord(::GI.MultiPointTrait, g::MultiPoint) = length(first(g))
 GI.ngeom(::GI.MultiPointTrait, g::MultiPoint) = length(g)
 GI.getgeom(::GI.MultiPointTrait, g::MultiPoint, i::Int) = Point(coordinates = g[i])
+GI.convert(::Type{<:MultiPoint}, ::GI.MultiPointTrait, geom) =
+    MultiPoint(; coordinates=coordinates(geom))
 
 GI.ncoord(::GI.MultiLineStringTrait, g::MultiLineString) = length(first(first(g)))
 GI.ngeom(::GI.MultiLineStringTrait, g::MultiLineString) = length(g)
 GI.getgeom(::GI.MultiLineStringTrait, g::MultiLineString, i::Int) =
     LineString(coordinates = g[i])
+GI.convert(::Type{<:MultiLineString}, ::GI.MultiLineStringTrait, geom) =
+    MultiLineString(; coordinates=coordinates(geom))
 
 GI.ncoord(::GI.MultiPolygonTrait, g::MultiPolygon) = length(first(first(first(g))))
 GI.ngeom(::GI.MultiPolygonTrait, g::MultiPolygon) = length(g)
 GI.getgeom(::GI.MultiPolygonTrait, g::MultiPolygon, i::Int) = Polygon(coordinates = g[i])
+GI.convert(::Type{<:MultiPolygon}, ::GI.MultiPolygonTrait, geom) =
+    MultiLineString(; coordinates=coordinates(geom))
 
 GI.ncoord(::GI.GeometryCollectionTrait, g::GeometryCollection) = GI.ncoord(first(g))
 GI.ngeom(::GI.GeometryCollectionTrait, g::GeometryCollection) = length(g)
-GI.getgeom(::GI.GeometryCollectionTrait, g::GeometryCollection, i::Int) = geometry(g[i])
+GI.getgeom(::GI.GeometryCollectionTrait, g::GeometryCollection, i::Int) = 
+function GI.convert(::Type{<:GeometryCollection}, ::GI.GeometryCollectionTrait, geom)
+    geometries = [GI.convert(Val{:GeoJSON}(), g) for g in GI.getgeoms(geom)]
+    GeometryCollection(; geometries)
+end
 
 # Feature
 GI.isfeature(::Type{<:Feature}) = true
 GI.trait(::Feature) = GI.FeatureTrait()
 GI.geometry(f::Feature) = geometry(f)
 GI.properties(f::Feature) = properties(f)
+function GI.convert(::Type{<:Feature}, ::GI.FeatureTrait, feature)
+    Feature(; 
+        geometry=GI.convert(GeoJSON, GI.geometry(feature)), 
+        properties=GI.properties(feature),
+    )
+end
 
 # FeatureCollection
 GI.isfeaturecollection(::Type{<:FeatureCollection}) = true
 GI.trait(::FeatureCollection) = GI.FeatureCollectionTrait()
 GI.getfeature(::GI.FeatureCollectionTrait, fc::FeatureCollection, i::Integer) = fc[i]
 GI.nfeature(::GI.FeatureCollectionTrait, fc::FeatureCollection) = length(fc)
+function GI.convert(::Type{<:FeatureCollection}, ::GI.FeatureCollectionTrait, fc)
+    FeatureCollection(GI.convert(Feature, GI.features(fc)))
+end
 
 # Any GeoJSON Object
 function GI.extent(x::GeoJSONObject)