Simplify

Implementation of the Ramer–Douglas–Peucker algorithm for reducing the number of points used to represent a curve.

Installation

defp deps do
  [{:simplify, "~> 1.0"}]
end

Usage

The Simplify module contains a function simplify that accepts a List of coordinates, each coordinate being a tuple {x, y}, and a tolerance. The function reduces the number of points by removing points that are less than the tolerance away from the simplified curve.

points = [{0, 0}, {0.05, 0.05}, {-0.05, 0.5}, {0, 1}, {0.05, 1.1}, {1, 1}, {0.5, 0.5}, {0, 0.0001}]

Simplify.simplify(points, 0.1) # => [{0, 0}, {0.05, 1.1}, {1, 1}, {0, 0.0001}]

The method will also take a Geo.LineString struct as created by the conversion functions in the Geo project (https://github.com/bryanjos/geo). This allows for easy import of GeoJSON or WKT/WKB formats. This version of the function returns a Geo.LineString of the simplified curve.

"{\"type\":\"LineString\":\"coordinates\":[[0,0],[0.05,0.05],[-0.05,0.5],[0,1],[0.05,1.1],[1,1],[0.5,0.5],[0,0.0001]]"
|> Jason.decode!
|> Geo.JSON.decode
|> Simplify.simplify(0.1)
|> Geo.JSON.encode
|> Jason.encode! # => "{\"coordinates\":[[0,0],[0.05,1.1],[1,1],[0,0.0001]],\"type\":\"LineString\"}"