mapit_area_centre_finder.js

#!/usr/local/bin/node

var _     = require('underscore'),
    rest  = require('restler'),
    async = require('async');


// Get the mapit ids from command line
var ids = _.rest(process.argv, 2);
console.log(ids);

// Run in series to avoid restler bug with getting the same content back for each request.
async.mapSeries(
  ids,
  getCentreForMapitArea,
  function (err, results) {
    var average = averageCentres(results);
    console.log("LonLat: %s,%s", average.lon, average.lat);
  }
);


function getCentreForMapitArea (areaID, cb) {
  var done = false;
  var url = "http://za-pombola.staging.mysociety.org/mapit/area/" + areaID + "/geometry";
  // console.log("GET %s", url);
  rest
    .get(url)
    .on("complete", function (result) {
      if (done) return; // restler calls complete several times. Known bug.
      done = true; 
      var centre = {
        lat: result.centre_lat,
        lon: result.centre_lon,
      };
      console.log(areaID, centre);
      cb(null, centre);
    });
}


function averageCentres (centres) {
  // This is not geographically correct, but good enough for an estimate on already approximated data.
  var count = centres.length;
  var lat_sum = _.chain(centres).pluck('lat').reduce(function (a,b) {return a+b}, 0 ).value();
  var lon_sum = _.chain(centres).pluck('lon').reduce(function (a,b) {return a+b}, 0 ).value();
  return {
    lat: lat_sum / count,
    lon: lon_sum / count
  };
}