postgistogeojson.js

/* 
 *   A function that converts a PostGIS query into a GeoJSON object.
 *   Copyright (C) 2012  Samuel Giles <sam@sam-giles.co.uk>
 *
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.

 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * Takes an array of associative objects/arrays and outputs a FeatureCollection object.  See <http://www.geojson.org/geojson-spec.html> example 1.1/
 * The Query that fetched the data would need to be similar to: 
 *              SELECT {field_list}, st_asgeojson(...) AS geojson FROM geotable
 * Where the "AS geojson" must be as is. Because the function relies on a "geojson" column.
 * 
 * @param queryResult The query result from the PostGIS database.  Format deduced from <https://gist.github.com/2146017>
 * @returns The equivalent GeoJSON object representation.
 */
function postGISQueryToFeatureCollection(queryResult) {
  // Initalise variables.
  var i = 0,
      length = queryResult.length,
      prop = null,
      geojson = {
        "type": "FeatureCollection",
        "features": []
      };    // Set up the initial GeoJSON object.

  for(i = 0; i < length; i++) {  // For each result create a feature
    var feature = {
      "type": "Feature",
      "geometry": JSON.parse(queryResult[i].geojson)
    };
    // finally for each property/extra field, add it to the feature as properties as defined in the GeoJSON spec.
    for(prop in queryResult[i]) {
      if (prop !== "geojson" && queryResult[i].hasOwnProperty(prop)) {
        feature[prop] = queryResult[i][prop];
      }
    }
    // Push the feature into the features array in the geojson object.
    geojson.features.push(feature);
  }
  // return the FeatureCollection geojson object.
  return geojson;
}

/*  ##########################         EXAMPLE              ######################################## */

// An array of ASSOCIATIVE results filled with two example results.
var queryResults = [
   {
      "geojson": '{"type": "Point", "coordinates": [102.0, 0.5]}',
      "prop0" : "value0"
   },
   {
      "geojson": '{ "type": "LineString","coordinates": [[102.0, 0.0], [103.0, 1.0], [104.0, 0.0], [105.0, 1.0]]}',
      "prop1": 0.0
   }];


var geoJson = postGISQueryToFeatureCollection(queryResults);