This is an implementation of Paul Bourke's CONREC algorithm in Elixir.

Conrex can be installed by adding conrex to your list of dependencies in mix.exs:

def deps do
  [
    {:conrex, "~> 1.0.0"}
  ]
end

The main algorithm outlined by Bourke can be invoked with Conrex.conrec:

iex> Conrex.conrec(values, x_coords, y_coords, contour_levels)

where values is a 2D list of samples (heights, travel times, etc), x_coords and y_coords are lists of X and Y coordinates for the sample grid, and contour_levels is a list of values at which a contour should be calculated. Conrex.conrec outputs a list of line segments to match the classic algorithm.

If the X and Y values are GPS coordinates, you can use Conrex.contour_polygons to generate GeoJSON polygons for each contour level:

iex> Conrex.contour_polygons(values, x_coords, y_coords, contour_levels, reference_point)

The additional parameter, reference_point, is a point known to be within the contour polygon, but outside any polygon holes. When converting the line segments to GeoJSON %Geo.Polygon{}s, Conrex will discard exterior polygon rings, and correct the coordinate winding for the main ring and the polygon holes to conform to the GeoJSON spec.

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Some of the tests will write output and sample data to a contour.js file, which can be used to visualize the test data and result. The visualization can be seen by viewing priv/static/index.html in a web browser.

MIT