Implement crstrait.

src/interface.jl

@@ -217,7 +217,9 @@ Note that this is only valid for [`AbstractCurveTrait`](@ref)s.
 """
 length(geom) = length(geomtrait(geom), geom)
 
+
 # Surface
+
 """
     area(geom) -> Number
 
@@ -226,6 +228,7 @@ Note that this is only valid for [`AbstractSurfaceTrait`](@ref)s.
 """
 area(geom) = area(geomtrait(geom), geom)
 
+
 """
     centroid(geom) -> Point
 
@@ -235,6 +238,7 @@ Note that this is only valid for [`AbstractSurfaceTrait`](@ref)s.
 """
 centroid(geom) = centroid(geomtrait(geom), geom)
 
+
 """
     pointonsurface(geom) -> Point
 
@@ -243,6 +247,7 @@ Note that this is only valid for [`AbstractSurfaceTrait`](@ref)s.
 """
 pointonsurface(geom) = pointonsurface(geomtrait(geom), geom)
 
+
 """
     boundary(geom) -> Curve
 
@@ -251,7 +256,9 @@ Note that this is only valid for [`AbstractSurfaceTrait`](@ref)s.
 """
 boundary(geom) = boundary(geomtrait(geom), geom)
 
+
 # Polygon/Triangle
+
 """
     nring(geom) -> Integer
 
@@ -670,3 +677,12 @@ astext(geom) = astext(geomtrait(geom), geom)
 Convert `geom` into Well Known Binary (WKB) representation, such as `000000000140000000000000004010000000000000`.
 """
 asbinary(geom) = asbinary(geomtrait(geom), geom)
+
+"""
+    crstrait(geom) -> AbstractCRSTrait
+
+Retrieves the type of the Coordinate Reference System for the given `geom`.
+Defaults to retrieving from `crs(geom)` and to `UnknownTrait` if not implemented.
+
+"""
+crstrait(geom) = UnknownTrait()

src/types.jl

@@ -93,6 +93,26 @@ abstract type AbstractFeatureCollectionTrait <: AbstractTrait end
 "A FeatureCollectionTrait holds objects of `FeatureTrait`"
 struct FeatureCollectionTrait <: AbstractFeatureCollectionTrait end
 
+"Supertype for all coordinate reference system traits"
+abstract type AbstractCRSTrait end
+
+"An AbstractProjectedTrait for all projected coordinate reference systems"
+abstract type AbstractProjectedTrait <: AbstractCRSTrait end
+"An AbstractGeographicTrait for all geographic coordinate reference systems"
+abstract type AbstractGeographicTrait <: AbstractCRSTrait end
+
+"An ProjectedTrait for all projected coordinate reference systems"
+struct ProjectedTrait <: AbstractProjectedTrait end
+"An GeographicTrait for all geographic coordinate reference systems"
+struct GeographicTrait <: AbstractGeographicTrait end
+"An UnknownTrait for all unknown (assumed projected) coordinate reference systems"
+struct UnknownTrait <: AbstractProjectedTrait
+    function UnknownTrait()
+        Base.depwarn("It is unknown whether your geometry is projected or geographic. Please implement `crstrait` for your geometry.", :UnknownTrait)
+        new()
+    end
+end
+
 "An AbstractRasterTrait for all rasters"
 abstract type AbstractRasterTrait <: AbstractTrait end
 struct RasterTrait <: AbstractRasterTrait end