Playing around with zip code distance algorithms and radius search

zip-distance.js

const ZIPCODES  = require('./zipcodes.js')
const sqlite    = require('sqlite')
const Promise   = require('bluebird')


// http://www.zipcodeapi.com/API

/**
 * Calculates distance between two ZIPCODES
 * @sauce: https://www.movable-type.co.uk/scripts/latlong.html
 * @param  {object}  zip1       Object containing zip, lat, lng
 * @param  {object}  zip2       Object containing zip, lat, lng
 * @param  {integer} PRECISION  Flag to return the result in kilometers or miles
 * @return {double}             A double representing the distance between the two points
 */
function zipDistance(zip1, zip2, PRECISION=3) {
    const R  = 6371
    // const R  = 6371e3 // meters
    // const M  = R / 1.609

    const φ1 = degressToRadians(zip1.lat)
    const φ2 = degressToRadians(zip2.lat)
    const Δφ = degressToRadians((zip2.lat-zip1.lat))
    const Δλ = degressToRadians((zip2.lng-zip1.lng))

    let a = Math.sin(Δφ/2) * Math.sin(Δφ/2) +
            Math.cos(φ1) * Math.cos(φ2) *
            Math.sin(Δλ/2) * Math.sin(Δλ/2)

    let c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a))

    return (R * c).toFixed(PRECISION)
}


/**
 * Calculate the lat and lng ranges for a given "radius"
 * @param  {[type]} zip1   [description]
 * @param  {[type]} radius [description]
 * @return {[type]}        [description]
 */
function getZipRadius(zip1, radius) {

    let DIST = 0.01035 * radius

    return {
        latMin: zip1.lat - DIST,
        latMax: zip1.lat + DIST,
        lngMin: zip1.lng - DIST,
        lngMax: zip1.lng + DIST,
    }
}


/**
 * [degressToRadians description]
 * @param  {[type]} degrees [description]
 * @return {[type]}         [description]
 */
function degressToRadians(degrees) {
  return degrees * (Math.PI/180)
}


/**
 * Converts Km to miles
 * @param  {float}  km      distance in kilometers
 * @return {double} miles   distance in miles
 */
function kmToMiles(km, PRECISION=3) {
    return (km / 1.609).toFixed(PRECISION)
}


/**
 * [getZipsInRadius description]
 * @param  {[type]} zip    [description]
 * @param  {[type]} zips   [description]
 * @param  {[type]} radius [description]
 * @return {[type]}        [description]
 */
function getZipsInRadius(zip, zips, radius) {

    const RADIUS = getZipRadius(zip, radius)

    return zips.filter(el => {
        if (RADIUS.latMin <= el.lat && el.lat <= RADIUS.latMax
        &&  RADIUS.lngMin <= el.lng && el.lng <= RADIUS.lngMax
        ) {

            let distance = zipDistance(zip, el)

            if (distance <= radius) {
                return el
            }
        }
    })
}





// const TARGET = ZIPCODES[0]
const RADIUS = 100


const TARGET = {
    lat: 30.3,
    lng: -97.6,
    zip_code: '???',
}


// let res = getZipsInRadius(TARGET, ZIPCODES, RADIUS)

// res.map(el => {
//     console.log(`distance from ${TARGET.zip_code} to ${el.zip_code} is`, kmToMiles(zipDistance(TARGET, el)), 'miles')
// })


getZipsInRadius(TARGET, ZIPCODES, RADIUS)
    .map(el => {
        console.log(`distance from ${TARGET.zip_code} to ${el.zip_code} is`, kmToMiles(zipDistance(TARGET, el)), 'miles')
    })