Compressing GeoJSON with informations loss

gistfile1.txt

/*
 pour lancer :
 node geoJsonMinifier.js <cheminDuFichierGeoJson> > <cheminDuFichierDeSorti>

 */

var fs = require('fs');
var _ = require('lodash');

var geoJsonPath = process.argv[2];
if (!geoJsonPath) {
  console.error("You must pass a path to a geoJson file", geoJsonPath);
  return;
}
fs.readFile(geoJsonPath, function (err, geoJsonContent) {
  if (err) {
    console.error("Error while reading file", err);
    return;
  }

  var geoJson = JSON.parse(geoJsonContent);

  if (geoJson.type != 'FeatureCollection') {
    console.error("The type of the geoJsonContent must be FeatureCollection", geoJson.type);
    return;
  }

  console.log(JSON.stringify(minifyGeoJson(geoJson)));
});

function minifyGeoJson(geoJson) {

  var minifiedFeatures = geoJson.features.map(function (feature) {
    var minifyCoordinate = _.flow(decreasePrecision(3), removeDuplicatePoint);
    var newCoordinates = minifyCoordinate(feature.geometry.coordinates);

    return {
      "type": "Feature",
      "id": feature.id,
      "properties": feature.properties,
      "geometry": {
        "type": feature.geometry.type,
        "coordinates": newCoordinates
      }
    };
  });

  return {
    "type": "FeatureCollection",
    "features": minifiedFeatures
  }
}

function isCoordinate(maybeCoordinates) {
  return _.isArray(maybeCoordinates) && maybeCoordinates.length == 2 && _.isNumber(maybeCoordinates[0]) && _.isNumber(maybeCoordinates[1])
}

function removeDuplicatePoint(arr) {
  var arrSize = arr.length;
  return arr.map(function(el) {
      if(_.isArray(el) ) {
        if(el.every(isCoordinate)) {
          var elSize = el.length;
          return el.filter(function(coordinates, idx) {
            //Minus 2 beacause we want at least 3 points
            if(idx > 0 && idx < elSize - 2) {
              return distanceBetweenCoordinates(coordinates, el[idx - 1]) > 100
            } else {
              return true;
            }
          });
        } else {
          return removeDuplicatePoint(el);
        }
      } else {
        return el;
      }
  })
}

function decreasePrecision(precision) {
  return function _decreasePrecision(arr) {
    var tenFactor = Math.pow(10, precision);

    return arr.map(function (el) {
      if (_.isArray(el)) {
        return _decreasePrecision(el);
      } else if (_.isNumber(el)) {
        return Math.round(el * tenFactor) / tenFactor;
      } else {
        return el;
      }
    })
  }
}

function toRadians(n) {
  return n * Math.PI / 180;
}

function distanceBetweenCoordinates(coord1, coord2) {
  var lon1 = coord1[0];
  var lat1 = coord1[1];
  var lon2 = coord2[0];
  var lat2 = coord2[1];

  var R = 6371000; // earth radius in meters
  var φ1 = toRadians(lat1);
  var φ2 = toRadians(lat2);
  var Δφ = toRadians(lat2-lat1);
  var Δλ = toRadians(lon2-lon1);

  var a = Math.sin(Δφ/2) * Math.sin(Δφ/2) +
      Math.cos(φ1) * Math.cos(φ2) *
      Math.sin(Δλ/2) * Math.sin(Δλ/2);
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));

  return R * c;
}