geojson-path-finder

GeoJSON Path Finder

Find shortest paths through a network of GeoJSON.

Given a network of GeoJSON LineStrings, GeoJSON Path Finder will find the shortest path between two points in the network. This might be useful for automatic route searches in smaller networks, where setting up a real route planner like OSRM is too much work, or you simply need to do everything on the client.

See the GeoJSON Path Finder demo.

Upgrade notice Version 2.0 has been released, which is a TypeScript rewrite - you can still use the module from plain JavaScript, of course. This version also contains some breaking changes regarding option naming; for most common use cases, everything will work as before.

Breaking changes:

• option precision is now named tolerance
• option keyFn is now named key
• option weightFn is now named weight
• option edgeDataReduceFn is now named edgeDataReducer
• option edgeDataSeed is now a function taking the properties of the start node

Installing

npm install --save geojson-path-finder

API

Detailed (and somewhat experimental) API Docs

Create a path finding object:

import PathFinder from "geojson-path-finder";
import geojson from "./network.json";

const pathFinder = new PathFinder(geojson);

The GeoJSON object should be a FeatureCollection of LineString features. The network will be built into a topology, so that lines that start and end, or cross, at the same coordinate are joined such that you can find a path from one feature to the other.

To find the shortest path between two coordinates:

var path = pathFinder.findPath(start, finish);

Where start and finish are two GeoJSON point features. Note that both points have to be vertices in the routing network; if they are not, no route will be found.

If a route can be found, an object with two properties: path and weight is returned, where path is the coordinates the path runs through, and weight is the total weight (distance in kilometers, if you use the default weight function) of the path.

As a convenience, the function pathToGeoJSON is also exported, it converts the result of a findPath call to a GeoJSON linestring:

import PathFinder, { pathToGeoJSON } from "geojson-path-finder";
const pathFinder = new PathFinder(geojson);
const pathLineString = pathToGeoJSON(pathFinder.findPath(start, finish));

(If findPath does not find a path, pathToGeoJSON will also return undefined.)

PathFinder options

The PathFinder constructor takes an optional seconds parameter containing options that you can use to control the behaviour of the path finder. Available options:

• weight controls how the weight (or cost) of travelling between two vertices is calculated; by default, the geographic distance between the coordinates is calculated and used as weight; see Weight functions below for details
• tolerance (default 1e-5) controls the tolerance for how close vertices in the GeoJSON can be before considered being the same vertice; you can say that coordinates closer than this will be snapped together into one coordinate
• edgeDataReducer can optionally be used to store data present in the GeoJSON on each edge of the routing graph; typically, this can be used for storing things like street names; if specified, the reduced data is present on found paths under the edgeDatas property
• edgeDataSeed is a function returning taking a network feature's properties as argument and returning the seed used when reducing edge data with the edgeDataReducer above

Weight functions

By default, the cost of going from one node in the network to another is determined simply by the geographic distance between the two nodes. This means that, by default, shortest paths will be found. You can however override this by providing a cost calculation function through the weight option:

const pathFinder = new PathFinder(geojson, {
  weight: function (a, b, props) {
    const dx = a[0] - b[0];
    const dy = a[1] - b[1];
    return Math.sqrt(dx * dx + dy * dy);
  },
});

The weight function is passed two coordinate arrays (in GeoJSON axis order), as well as the feature properties that are associated with this feature, and should return either:

• a numeric value for the cost of travelling between the two coordinates; in this case, the cost is assumed to be the same going from a to b as going from b to a; as cost of 0 means the edge can't be used
• an object with two properties: forward and backward; in this case, forward denotes the cost of going from a to b, and backward the cost of going from b to a; setting either to 0 will prevent taking that direction, the segment will be a oneway.
• undefined is the same as setting the weight to 0: this edge can't be used