svg-transit-map/lib/normalize.js

Draw an SVG transit map for a given transport network graph with position information.

'use strict'

const sum = require('lodash/sum')

const clone = x => JSON.parse(JSON.stringify(x))

// normalize average edge length to 1
const normalize = (_graph, invertY = false) => {
	const graph = clone(_graph)

	const edgeLengths = graph.edges.map(e => {
		const source = graph.nodes.find(n => n.id === e.source).metadata
		const target = graph.nodes.find(n => n.id === e.target).metadata

		return Math.sqrt(Math.pow(source.x - target.x, 2) + Math.pow(source.y - target.y, 2))
	})

	const averageEdgeLength = sum(edgeLengths) / edgeLengths.length
	const scalar = 1 / averageEdgeLength

	for (const node of graph.nodes) {
		node.metadata.x *= scalar
		node.metadata.y *= scalar * (invertY ? (-1) : 1)
	}

	return graph
}

module.exports = normalize