node-hgt/src/sync-tile-set.js

Query hgt files (typically SRTM elevation data) with performance.

var extend = require('extend'),
    ImagicoElevationDownloader = require('./imagico'),
    loadTile = require('./load-tile'),
    _latLng = require('./latlng');

function range(start, end) {
    var a = Array.apply(0, new Array(end - start + 1));
    a.forEach(function(e, i) { a[i] = start + i; });
    return a;
}

function flatten(a) {
    return [].concat.apply([], a);
}

function SyncTileSet(tileDir, sw, ne, cb, options) {
    this.options = extend({}, {
        loadTile: loadTile,
        downloader: new ImagicoElevationDownloader(tileDir),
        pad: 0
    }, options);
    this._tileDir = tileDir;

    var pad = this.options.pad,
        south = Math.floor(sw[0]) - pad,
        north = Math.floor(ne[0]) + 1 + pad,
        west = Math.floor(sw[1]) - pad,
        east = Math.floor(ne[1]) + 1 + pad;

    this._tiles = new Array(north - south);
    this._south = south;
    this._west = west;
    this._north = north;
    this._east = east;

    var _loadTile = this.options.loadTile.bind(this),
        _this = this,
        tasks = flatten(range(south, north - 1).map(function(lat, i) {
            this._tiles[i] = new Array(east - west);
            return range(west, east - 1).map(function(lng, j) {
                return function() {
                    _loadTile(this._tileDir, new _latLng([lat, lng]), function(err, t) {
                        if (err) {
                            return setImmediate(taskCb(err));
                        }
                        this._tiles[i][j] = t;
                        setImmediate(taskCb);
                    }.bind(_this));
                }.bind(_this);
            });
        }.bind(_this))),
        wait = tasks.length,
        taskCb = function(err) {
            if (wait < 0) return;

            if (err) {
                wait = -1;
                return setImmediate(cb(err));
            }

            wait--;
            if (wait === 0) {
                setImmediate(function() {
                    cb();
                });
            }
        };

    tasks.forEach(function(t) { t(); });
}

SyncTileSet.prototype.getElevation = function(ll) {
    var tileLat = Math.floor(ll[0]),
        tileLng = Math.floor(ll[1]),
        tile;

    if (tileLat < this._south || tileLat >= this._north ||
        tileLng < this._west || tileLng >= this._east) {
        throw new Error('Coordinate is outside tileset\'s bounds: ' + ll);
    }

    tile = this._tiles[tileLat - this._south][tileLng - this._west];
    return tile.getElevation(ll);
};

SyncTileSet.prototype.destroy = function() {
    this._tiles.forEach(function(arr) {
        arr.forEach(function(t) {
            t.destroy();
        });
    });
};

module.exports = SyncTileSet;