arcgistogeojson.js

/*
 * Copyright 2017 Esri
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

// checks if 2 x,y points are equal
function pointsEqual (a, b) {
  for (var i = 0; i < a.length; i++) {
    if (a[i] !== b[i]) {
      return false;
    }
  }
  return true;
}

// checks if the first and last points of a ring are equal and closes the ring
function closeRing (coordinates) {
  if (!pointsEqual(coordinates[0], coordinates[coordinates.length - 1])) {
    coordinates.push(coordinates[0]);
  }
  return coordinates;
}

// determine if polygon ring coordinates are clockwise. clockwise signifies outer ring, counter-clockwise an inner ring
// or hole. this logic was found at http://stackoverflow.com/questions/1165647/how-to-determine-if-a-list-of-polygon-
// points-are-in-clockwise-order
function ringIsClockwise (ringToTest) {
  var total = 0;
  var i = 0;
  var rLength = ringToTest.length;
  var pt1 = ringToTest[i];
  var pt2;
  for (i; i < rLength - 1; i++) {
    pt2 = ringToTest[i + 1];
    total += (pt2[0] - pt1[0]) * (pt2[1] + pt1[1]);
    pt1 = pt2;
  }
  return (total >= 0);
}

// ported from terraformer.js https://github.com/Esri/Terraformer/blob/master/terraformer.js#L504-L519
function vertexIntersectsVertex (a1, a2, b1, b2) {
  var uaT = ((b2[0] - b1[0]) * (a1[1] - b1[1])) - ((b2[1] - b1[1]) * (a1[0] - b1[0]));
  var ubT = ((a2[0] - a1[0]) * (a1[1] - b1[1])) - ((a2[1] - a1[1]) * (a1[0] - b1[0]));
  var uB = ((b2[1] - b1[1]) * (a2[0] - a1[0])) - ((b2[0] - b1[0]) * (a2[1] - a1[1]));

  if (uB !== 0) {
    var ua = uaT / uB;
    var ub = ubT / uB;

    if (ua >= 0 && ua <= 1 && ub >= 0 && ub <= 1) {
      return true;
    }
  }

  return false;
}

// ported from terraformer.js https://github.com/Esri/Terraformer/blob/master/terraformer.js#L521-L531
function arrayIntersectsArray (a, b) {
  for (var i = 0; i < a.length - 1; i++) {
    for (var j = 0; j < b.length - 1; j++) {
      if (vertexIntersectsVertex(a[i], a[i + 1], b[j], b[j + 1])) {
        return true;
      }
    }
  }

  return false;
}

// ported from terraformer.js https://github.com/Esri/Terraformer/blob/master/terraformer.js#L470-L480
function coordinatesContainPoint (coordinates, point) {
  var contains = false;
  for (var i = -1, l = coordinates.length, j = l - 1; ++i < l; j = i) {
    if (((coordinates[i][1] <= point[1] && point[1] < coordinates[j][1]) ||
         (coordinates[j][1] <= point[1] && point[1] < coordinates[i][1])) &&
        (point[0] < (((coordinates[j][0] - coordinates[i][0]) * (point[1] - coordinates[i][1])) / (coordinates[j][1] - coordinates[i][1])) + coordinates[i][0])) {
      contains = !contains;
    }
  }
  return contains;
}

// ported from terraformer-arcgis-parser.js https://github.com/Esri/terraformer-arcgis-parser/blob/master/terraformer-arcgis-parser.js#L106-L113
function coordinatesContainCoordinates (outer, inner) {
  var intersects = arrayIntersectsArray(outer, inner);
  var contains = coordinatesContainPoint(outer, inner[0]);
  if (!intersects && contains) {
    return true;
  }
  return false;
}

// do any polygons in this array contain any other polygons in this array?
// used for checking for holes in arcgis rings
// ported from terraformer-arcgis-parser.js https://github.com/Esri/terraformer-arcgis-parser/blob/master/terraformer-arcgis-parser.js#L117-L172
function convertRingsToGeoJSON (rings) {
  var outerRings = [];
  var holes = [];
  var x; // iterator
  var outerRing; // current outer ring being evaluated
  var hole; // current hole being evaluated

  // for each ring
  for (var r = 0; r < rings.length; r++) {
    var ring = closeRing(rings[r].slice(0));
    if (ring.length < 4) {
      continue;
    }
    // is this ring an outer ring? is it clockwise?
    if (ringIsClockwise(ring)) {
      var polygon = [ ring.slice().reverse() ]; // wind outer rings counterclockwise for RFC 7946 compliance
      outerRings.push(polygon); // push to outer rings
    } else {
      holes.push(ring.slice().reverse()); // wind inner rings clockwise for RFC 7946 compliance
    }
  }

  var uncontainedHoles = [];

  // while there are holes left...
  while (holes.length) {
    // pop a hole off out stack
    hole = holes.pop();

    // loop over all outer rings and see if they contain our hole.
    var contained = false;
    for (x = outerRings.length - 1; x >= 0; x--) {
      outerRing = outerRings[x][0];
      if (coordinatesContainCoordinates(outerRing, hole)) {
        // the hole is contained push it into our polygon
        outerRings[x].push(hole);
        contained = true;
        break;
      }
    }

    // ring is not contained in any outer ring
    // sometimes this happens https://github.com/Esri/esri-leaflet/issues/320
    if (!contained) {
      uncontainedHoles.push(hole);
    }
  }

  // if we couldn't match any holes using contains we can try intersects...
  while (uncontainedHoles.length) {
    // pop a hole off out stack
    hole = uncontainedHoles.pop();

    // loop over all outer rings and see if any intersect our hole.
    var intersects = false;

    for (x = outerRings.length - 1; x >= 0; x--) {
      outerRing = outerRings[x][0];
      if (arrayIntersectsArray(outerRing, hole)) {
        // the hole is contained push it into our polygon
        outerRings[x].push(hole);
        intersects = true;
        break;
      }
    }

    if (!intersects) {
      outerRings.push([hole.reverse()]);
    }
  }

  if (outerRings.length === 1) {
    return {
      type: 'Polygon',
      coordinates: outerRings[0]
    };
  } else {
    return {
      type: 'MultiPolygon',
      coordinates: outerRings
    };
  }
}

// This function ensures that rings are oriented in the right directions
// outer rings are clockwise, holes are counterclockwise
// used for converting GeoJSON Polygons to ArcGIS Polygons
function orientRings (poly) {
  var output = [];
  var polygon = poly.slice(0);
  var outerRing = closeRing(polygon.shift().slice(0));
  if (outerRing.length >= 4) {
    if (!ringIsClockwise(outerRing)) {
      outerRing.reverse();
    }

    output.push(outerRing);

    for (var i = 0; i < polygon.length; i++) {
      var hole = closeRing(polygon[i].slice(0));
      if (hole.length >= 4) {
        if (ringIsClockwise(hole)) {
          hole.reverse();
        }
        output.push(hole);
      }
    }
  }

  return output;
}

// This function flattens holes in multipolygons to one array of polygons
// used for converting GeoJSON Polygons to ArcGIS Polygons
function flattenMultiPolygonRings (rings) {
  var output = [];
  for (var i = 0; i < rings.length; i++) {
    var polygon = orientRings(rings[i]);
    for (var x = polygon.length - 1; x >= 0; x--) {
      var ring = polygon[x].slice(0);
      output.push(ring);
    }
  }
  return output;
}

// shallow object clone for feature properties and attributes
// from http://jsperf.com/cloning-an-object/2
function shallowClone (obj) {
  var target = {};
  for (var i in obj) {
    if (obj.hasOwnProperty(i)) {
      target[i] = obj[i];
    }
  }
  return target;
}

function getId (attributes, idAttribute) {
  var keys = idAttribute ? [idAttribute, 'OBJECTID', 'FID'] : ['OBJECTID', 'FID'];
  for (var i = 0; i < keys.length; i++) {
    var key = keys[i];
    if (
      key in attributes &&
      (typeof attributes[key] === 'string' ||
        typeof attributes[key] === 'number')
    ) {
      return attributes[key];
    }
  }
  throw Error('No valid id attribute found');
}

function arcgisToGeoJSON (arcgis, idAttribute) {
  var geojson = {};

  if (arcgis.features) {
    geojson.type = 'FeatureCollection';
    geojson.features = [];
    for (var i = 0; i < arcgis.features.length; i++) {
      geojson.features.push(arcgisToGeoJSON(arcgis.features[i], idAttribute));
    }
  }

  if (typeof arcgis.x === 'number' && typeof arcgis.y === 'number') {
    geojson.type = 'Point';
    geojson.coordinates = [arcgis.x, arcgis.y];
    if (typeof arcgis.z === 'number') {
      geojson.coordinates.push(arcgis.z);
    }
  }

  if (arcgis.points) {
    geojson.type = 'MultiPoint';
    geojson.coordinates = arcgis.points.slice(0);
  }

  if (arcgis.paths) {
    if (arcgis.paths.length === 1) {
      geojson.type = 'LineString';
      geojson.coordinates = arcgis.paths[0].slice(0);
    } else {
      geojson.type = 'MultiLineString';
      geojson.coordinates = arcgis.paths.slice(0);
    }
  }

  if (arcgis.rings) {
    geojson = convertRingsToGeoJSON(arcgis.rings.slice(0));
  }

  if (
    typeof arcgis.xmin === 'number' &&
    typeof arcgis.ymin === 'number' &&
    typeof arcgis.xmax === 'number' &&
    typeof arcgis.ymax === 'number'
  ) {
    geojson.type = 'Polygon';
    geojson.coordinates = [[
      [arcgis.xmax, arcgis.ymax],
      [arcgis.xmin, arcgis.ymax],
      [arcgis.xmin, arcgis.ymin],
      [arcgis.xmax, arcgis.ymin],
      [arcgis.xmax, arcgis.ymax],
    ]];
  }

  if (arcgis.geometry || arcgis.attributes) {
    geojson.type = 'Feature';
    geojson.geometry = (arcgis.geometry) ? arcgisToGeoJSON(arcgis.geometry) : null;
    geojson.properties = (arcgis.attributes) ? shallowClone(arcgis.attributes) : null;
    if (arcgis.attributes) {
      try {
        geojson.id = getId(arcgis.attributes, idAttribute);
      } catch (err) {
        // don't set an id
      }
    }
  }

  // if no valid geometry was encountered
  if (JSON.stringify(geojson.geometry) === JSON.stringify({})) {
    geojson.geometry = null;
  }

  if (
    arcgis.spatialReference &&
    arcgis.spatialReference.wkid &&
    arcgis.spatialReference.wkid !== 4326
  ) {
    console.warn('Object converted in non-standard crs - ' + JSON.stringify(arcgis.spatialReference));
  }

  return geojson;
}

function geojsonToArcGIS (geojson, idAttribute) {
  idAttribute = idAttribute || 'OBJECTID';
  var spatialReference = { wkid: 4326 };
  var result = {};
  var i;

  switch (geojson.type) {
    case 'Point':
      result.x = geojson.coordinates[0];
      result.y = geojson.coordinates[1];
      result.spatialReference = spatialReference;
      break;
    case 'MultiPoint':
      result.points = geojson.coordinates.slice(0);
      result.spatialReference = spatialReference;
      break;
    case 'LineString':
      result.paths = [geojson.coordinates.slice(0)];
      result.spatialReference = spatialReference;
      break;
    case 'MultiLineString':
      result.paths = geojson.coordinates.slice(0);
      result.spatialReference = spatialReference;
      break;
    case 'Polygon':
      result.rings = orientRings(geojson.coordinates.slice(0));
      result.spatialReference = spatialReference;
      break;
    case 'MultiPolygon':
      result.rings = flattenMultiPolygonRings(geojson.coordinates.slice(0));
      result.spatialReference = spatialReference;
      break;
    case 'Feature':
      if (geojson.geometry) {
        result.geometry = geojsonToArcGIS(geojson.geometry, idAttribute);
      }
      result.attributes = (geojson.properties) ? shallowClone(geojson.properties) : {};
      if (geojson.id) {
        result.attributes[idAttribute] = geojson.id;
      }
      break;
    case 'FeatureCollection':
      result = [];
      for (i = 0; i < geojson.features.length; i++) {
        result.push(geojsonToArcGIS(geojson.features[i], idAttribute));
      }
      break;
    case 'GeometryCollection':
      result = [];
      for (i = 0; i < geojson.geometries.length; i++) {
        result.push(geojsonToArcGIS(geojson.geometries[i], idAttribute));
      }
      break;
  }

  return result;
}