Geo

A collection of GIS functions. Handles conversions to and from WKT, WKB, and GeoJSON for the following geometries:

• Point
• LineString
• Polygon
• MultiPoint
• MulitLineString
• MultiPolygon
• GeometryCollection

Examples

• Encode and decode WKT and EWKT

iex(1)> point = Geo.WKT.decode("POINT(30 -90)")
%Geo.Point{ coordinates: {30, -90}, srid: nil}

iex(2)> Geo.WKT.encode(point)
"POINT(30 -90)"

iex(3)> point = Geo.WKT.decode("SRID=4326;POINT(30 -90)")
%Geo.Point{coordinates: {30, -90}, srid: 4326}

• Encode and decode WKB and EWKB

iex(1)> point = Geo.WKB.decode("0101000000000000000000F03F000000000000F03F")
%Geo.Point{ coordinates: {1.0, 1.0}, srid: nil }

iex(2)> Geo.WKB.encode(point)
"00000000013FF00000000000003FF0000000000000"

iex(3)> point = Geo.WKB.decode("0101000020E61000009EFB613A637B4240CF2C0950D3735EC0")
%Geo.Point{ coordinates: {36.9639657, -121.8097725}, srid: 4326 }

iex(4)> Geo.WKB.encode(point)
"0020000001000010E640427B633A61FB9EC05E73D350092CCF"

• Encode and decode GeoJSON

iex(1)> point = Geo.JSON.decode("{ "type": "Point", "coordinates": [100.0, 0.0] }")
%Geo.Point{ coordinates: {100.0, 0.0}, srid: nil }

iex(2)> Geo.JSON.encode(point)
"{"type":"Point","coordinates":[100.0,0.0]}"

• Encoder, Decoder, and Formatter to be used with Postgrex for PostGIS data types

opts = [hostname: "localhost", username: "postgres", database: "geo_postgrex_test",
encoder: &Geo.PostGIS.encoder/3, decoder: &Geo.PostGIS.decoder/4,
formatter: &Geo.PostGIS.formatter/1 ]

[hostname: "localhost", username: "postgres", database: "geo_postgrex_test",
 encoder: &Geo.PostGIS.encoder/3, decoder: &Geo.PostGIS.decoder/4,
 formatter: &Geo.PostGIS.formatter/1]

{:ok, pid} = Postgrex.Connection.start_link(opts)
{:ok, #PID<0.115.0>}

geo = %Geo.Point{coordinates: {30, -90}, srid: 4326}
%Geo.Point{coordinates: {30, -90}, srid: 4326}

{:ok, _} = Postgrex.Connection.query(pid, "CREATE TABLE point_test (id int, geom geometry(Point, 4326))")
{:ok, %Postgrex.Result{columns: nil, command: :create_table, num_rows: 0, rows: nil}}

{:ok, _} = Postgrex.Connection.query(pid, "INSERT INTO point_test VALUES ($1, $2)", [42, geo])
{:ok, %Postgrex.Result{columns: nil, command: :insert, num_rows: 1, rows: nil}}

Postgrex.Connection.query(pid, "SELECT * FROM point_test")
{:ok, %Postgrex.Result{columns: ["id", "geom"], command: :select, num_rows: 1,
rows: [{42, %Geo.Point{coordinates: {30.0, -90.0}, srid: 4326 }}]}}

• Can now be used with Ecto as well

#Add encoder, decoder, and formatter to your repo config
config :thanks, Repo,
  database: "geo_postgrex_test",
  username: "postgres",
  password: "postgres",
  hostname: "localhost",
  encoder:  &Geo.PostGIS.encoder/3, 
  decoder:  &Geo.PostGIS.decoder/4,
  formatter: &Geo.PostGIS.formatter/1


#Create a model
defmodule Test do
  use Ecto.Model

  schema "test" do
    field :name,           :string
    field :geom,           Geo.Point
  end
end

#Geometry columns can be created in migrations too
defmodule Repo.Migrations.Init do
  use Ecto.Migration

  def up do
    create table(:test) do
      add :name,     :string
      add :geom,     :geometry
    end
  end

  def down do
    drop table(:test)
  end
end