Merge pull request #15 from jgaskins/add-ewkt-and-ewkb

Add serialization to Well Known Text/Binary formats for `Geo::Coord`

spec/geo/coord_spec.cr

@@ -111,6 +111,57 @@ describe Geo::Coord do
     geojson.should be_a(GeoJSON::Coordinates)
   end
 
+  describe "#to_wkt" do
+    it "generates a Well Known Text format" do
+      coord = Geo::Coord.new(50.004444, 36.231389)
+
+      ewkt = coord.to_wkt
+
+      ewkt.should eq "POINT(36.231389 50.004444)"
+    end
+  end
+
+  describe "#to_wkb" do
+    it "generates a Well Known Binary format" do
+      coord = Geo::Coord.new(12, 34)
+
+      ewkb = coord.to_wkb
+
+      ewkb.should eq Bytes[
+        0,                       # Big-Endian
+        0, 0, 0, 1,              # POINT
+        0, 0, 0, 34, 0, 0, 0, 0, # Longitude encoded as IEEE-754
+        0, 0, 0, 12, 0, 0, 0, 0, # Latitude encoded as IEEE-754
+      ]
+    end
+  end
+
+  describe "#to_ewkt" do
+    it "generates an Extended Well Known Text format" do
+      coord = Geo::Coord.new(50.004444, 36.231389)
+
+      ewkt = coord.to_ewkt
+
+      ewkt.should eq "SRID=4326;POINT(36.231389 50.004444)"
+    end
+  end
+
+  describe "#to_ewkb" do
+    it "generates an Extended Well Known Binary format" do
+      coord = Geo::Coord.new(12, 34)
+
+      ewkb = coord.to_ewkb
+
+      ewkb.should eq Bytes[
+        0,                       # Big-Endian
+        0, 0, 0, 1,              # POINT
+        0, 0, 0, 34, 0, 0, 0, 0, # Longitude encoded as IEEE-754
+        0, 0, 0, 12, 0, 0, 0, 0, # Latitude encoded as IEEE-754
+        16, 140,                 # SRID 4326
+      ]
+    end
+  end
+
   describe "comparisons" do
     describe "equality" do
       pos1 = Geo::Coord.new(45.3142533036254, -93.47527313511819)

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

@@ -170,6 +170,46 @@ module Geo
       io << strfcoord(%{%latd°%latm'%lats"%lath %lngd°%lngm'%lngs"%lngh})
     end
 
+    def to_ewkt : String
+      String.build { |str| to_ewkt str }
+    end
+
+    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, 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
+      to_wkb bytes, byte_format
+      # SRID 4326 is used for latitude and longitude
+      # https://epsg.org/crs_4326/WGS-84.html
+      byte_format.encode 4236i16, bytes + 21
+
+      bytes
+    end
+
+    def to_wkt : String
+      String.build { |str| to_wkt str }
+    end
+
+    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 << ')' if output_parentheses
+    end
+
+    def to_wkb(bytes : Bytes = Bytes.new(21), byte_format : IO::ByteFormat = IO::ByteFormat::BigEndian) : Bytes
+      bytes[0] = 0                  # Big Endian
+      byte_format.encode 1u32, bytes + 1 # POINT type
+      byte_format.encode lng, bytes + 5
+      byte_format.encode lat, bytes + 13
+
+      bytes
+    end
+
     def ll
       {lat, lng}
     end

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