laneify/lib/geoTools.js

Create offset GeoJSON LineString features (lanes) based on an OSM way (road)

'use strict';

var Point = function (x, y) {
  return {
    x: x,
    y: y
  }
}

var Line = function (point1, point2) {
  return {
    p1: point1,
    p2: point2
  }
}

function add(point1, point2) {
  return new Point(point1.x + point2.x, point1.y + point2.y)
}

function multiply(point, scalar) {
  return new Point(point.x * scalar, point.y * scalar)
}

function getVector(line) {
  var p1 = line.p1,
      p2 = line.p2

  return new Point((p1.x - p2.x), (p1.y - p2.y))
}

function vectorLength(vector) {
  return Math.sqrt(Math.pow(vector.x, 2) + Math.pow(vector.y, 2))
}

/**
 * In the simple case of 90 degree rotation, the vector rotation
 * transform simplifies to x' = -y, y' = x
 * @param  {[type]} vec [description]
 * @return {[type]}     [description]
 */
function normalVector(vec) {
  var newX = -vec.y
  var newY = vec.x

  return new Point(newX, newY)
}

/**
 * Normalising a vector turns it into the unit vector
 * representation of itself, i.e. it's length is 1
 * @param  {Point} vector
 * @return {Point}        Unit vector
 */
function normalise(vector) {
  var length = vectorLength(vector)

  return new Point(vector.x/length, vector.y/length)
}

var geoTools = {
  createLine: function getLine(p1, p2) {
    return new Line(p1, p2)
  },
  createPoint: function getPoint(x, y) {
    return new Point(x, y)
  },
  unitNormal: function getUnitNormal(line) {
    return normalise(normalVector(getVector(line)))
  },
  translate: function translatePoint(point, unitVector, distance) {
    return add(point, multiply(unitVector, distance))
  }
}

module.exports = geoTools