Add Polygon#to_wkt

spec/geo/polygon_spec.cr

@@ -119,6 +119,19 @@ describe Geo::Polygon do
     geojson.should be_a(GeoJSON::Polygon)
   end
 
+  describe "#to_wkt" do
+    it "outputs a Well Known Text format" do
+      polygon = Geo::Polygon.new([
+        Geo::Coord.new(10, 30),
+        Geo::Coord.new(20, 10),
+        Geo::Coord.new(40, 20),
+        Geo::Coord.new(40, 40),
+      ])
+
+      polygon.to_wkt.should eq "POLYGON((30 10, 10 20, 20 40, 40 40, 30 10))"
+    end
+  end
+
   describe "comparisons" do
     describe "equality" do
       polygon1 = Geo::Polygon.new([pos1, pos2])

src/geo/coord.cr

@@ -174,11 +174,11 @@ module Geo
       String.build { |str| to_ewkt str }
     end
 
-    def to_ewkt(io : IO) : Nil
+    def to_ewkt(io : IO, output_type = true, output_parentheses = true) : Nil
       # SRID 4326 is used for latitude and longitude
       # https://epsg.org/crs_4326/WGS-84.html
       io << "SRID=4326;"
-      to_wkt io
+      to_wkt io, output_type: output_type, output_parentheses: output_parentheses
     end
 
     def to_ewkb(bytes : Bytes = Bytes.new(23), byte_format : IO::ByteFormat = IO::ByteFormat::BigEndian) : Bytes
@@ -194,10 +194,11 @@ module Geo
       String.build { |str| to_wkt str }
     end
 
-    def to_wkt(io : IO) : Nil
-      io << "POINT("
+    def to_wkt(io : IO, output_type = true, output_parentheses = true) : Nil
+      io << "POINT" if output_type
+      io << '(' if output_parentheses
       io << lng << ' ' << lat
-      io << ')'
+      io << ')' if output_parentheses
     end
 
     def to_wkb(bytes : Bytes = Bytes.new(21), byte_format : IO::ByteFormat = IO::ByteFormat::BigEndian) : Bytes

src/geo/polygon.cr

@@ -106,6 +106,21 @@ module Geo
       GeoJSON::Polygon.new([coordinates])
     end
 
+    def to_wkt : String
+      String.build { |str| to_wkt str }
+    end
+
+    def to_wkt(io : IO) : Nil
+      io << "POLYGON(("
+      @coords.each_with_index 1 do |coord, index|
+        coord.to_wkt io, output_type: false, output_parentheses: false
+        if index < @coords.size
+          io << ", "
+        end
+      end
+      io << "))"
+    end
+
     private def calculate_centroid : Geo::Coord
       centroid_lat = 0.0
       centroid_lng = 0.0