terriajs/lib/Map/Reproject.js

Geospatial data visualization platform.

'use strict';

/*global require*/
var proj4 = require('proj4').default;
var loadText = require('../Core/loadText');
var defined = require('terriajs-cesium/Source/Core/defined');
var Proj4Definitions = require('../Map/Proj4Definitions');
var urijs = require('urijs');
var when = require('terriajs-cesium/Source/ThirdParty/when');

var Reproject = {
    TERRIA_CRS: 'EPSG:4326',

    /**
     * Convert a CRS string into a code that Proj4 understands.
     * @param {String} crsString A CRS URI
     * @return {String} A code that is recognised by Proj4 as a valid CRS code.
     */
    crsStringToCode: function(crsString) {
        var crs = crsString.toLowerCase();
        var code;
        if (crs.indexOf('epsg:') === 0) {
            code = crsString.toUpperCase();
        } else if (crs.indexOf('urn:ogc:def:crs:epsg::') === 0) {
            code = 'EPSG:' + crsString.substring('urn:ogc:def:crs:EPSG::'.length);
        } else if (crs.indexOf('urn:ogc:def:crs:epsg') === 0) {
            // With version
            code = 'EPSG:' + crsString.substring('urn:ogc:def:crs:EPSG::x.x'.length);
        } else if (crs.indexOf('crs84') !== -1) {
            code = this.TERRIA_CRS;
        }
        return code;
    },

    /**
     * A point will need reprojecting if it isn't using the same (or equivalent) CRS as TerriaJS.
     * TerriaJS is assumed to be using EPSG:4326.
     *
     * If the code is not defined, it's assumed that the point/s will not need reprojecting as we don't know what the
     * source is, so we can't reproject anyway.
     *
     * @param {String} code A CRS code that Proj4 recognises.
     * @return {Bool} whether points in the CRS provided will need reprojecting.
     */
    willNeedReprojecting: function(code) {
        if (!defined(code) || code === this.TERRIA_CRS || code === 'EPSG:4283') {
            return false;
        }
        return true;
    },

    /**
     * Reproject points from one CRS to another.
     * @param {Array} coordinates which are two floating point numbers in an array in order long, lat.
     * @param {String} sourceCode The Proj4 code for the CRS the source coordinates are in.
     * @param {String} destCode The Proj4 code for the CRS the generated coordinates should be in.
     * @return {Array} coordinates in destCode CRS projection, two floating points in order long, lat.
     */
    reprojectPoint: function(coordinates, sourceCode, destCode) {
        var source = new proj4.Proj(Proj4Definitions[sourceCode]);
        var dest = new proj4.Proj(Proj4Definitions[destCode]);
        return proj4(source, dest, coordinates);
    },

    /**
     * Add the reprojection parameters to proj4 if the code is not already known by Proj4.
     * @param {String} proj4ServiceBaseUrl URL relative to Terria for accessing the proj4 service
     * @param {String} code The Proj4 CRS code to check for and potentially add
     * @return {Promise} Eventually resolves to false if code wasn't there and wasn't able to be added
     */
    checkProjection: function(proj4ServiceBaseUrl, code) {
        if (Proj4Definitions.hasOwnProperty(code)) {
            return true;
        }

        var url = new urijs(proj4ServiceBaseUrl).segment(code).toString();
        return when(loadText(url), function (proj4Text) {
                Proj4Definitions[code] = proj4Text;
                console.log('Added new string for', code, '=', proj4Text);
                return true;
            }, function(err) {
                return false;
            });
     }
};

module.exports = Reproject;