Proj is an Elixir library for converting coordinates between different coordinate systems, using Erlang NIFs to the OSGeo PROJ.4 library.
Proj also supports geodesic functions from PROJ.4. A geodesic is the shortest line around the globe which crosses through two points. This is useful for solving problems such as:
-
Finding the distance between two locations
-
Finding the bearings between two locations
-
Finding the resulting location after moving
xmetres forwards facing a certain bearing from a given location -
Plotting a set of points in a line between two locations
Before you can install Proj, you must have:
- gcc
- PROJ.4 newer than 4.9.0 (PROJ 5+ should work, but this library makes use of the legacy PROJ.4 API.)
apt install libproj-dev gcc binutils libc-dev make
yum install proj-devel binutils gcc glibc-devel make
brew install proj
Proj has currently only been tested on GNU/Linux and Mac OS X. Windows support has not yet been tested and may require some small changes to work under a Cygwin or MinGW environment.
iex> {:ok, bng} = Proj.from_epsg(27700) # British National Grid CRS is EPSG:27700
{:ok, #Proj<+init=epsg:27700 ...>}
# Convert the British National Grid Easting + Northing of Buckingham Palace into
# a Latitude + Longitude pair
iex> Proj.to_lat_lng!({529155, 179699}, bng)
{51.50147938477216, -0.1406319210455952}
# Convert the Latitude + Longitude of Buckingham Palace to its
# British National Grid Easting + Northing
iex> Proj.from_lat_lng!({51.501479, -0.140631}, bng)
{529155.0658918166, 179698.9583449281}
# Calculate the shortest distance "as the crow flies" in metres between
# Buckingham Palace and the Eiffel Tower
iex> Proj.Geodesic.distance({51.501476, -0.140634}, {48.8584, 2.2945})
341549.6819692767
# Calculate the resulting location after travelling 100 metres forwards from
# Buckingham Palace, facing a bearing of 060°
iex> Proj.Geodesic.travel({51.501476, -0.140634}, 60, 100)
{51.50192539979596, -0.1393868003258145}