SeedJS

SeedJS is a JavaScript library for seeding tiles from sources like WMTS or WMS and storing them into a storage like CouchDB.

Current features and limitations:

• plain JS, no jQuery/OL/etc. dependencies
• async API for background seeding
• requires HTLM5 Canvas and CORS support
• only supports a OSM/Google Maps compatible tile grid
• EPSG:3857 only, no reprojection of WMS sources and no meta-tiling
• MIT License

Current status: SeedJS is a proof of concept/prototype.

By default, you can only seed from local sources and can only store tiles in local databases due to the security restrictions of most browsers, where local means same domain and same port. To work around this limitation you need either sources/databases that support CORS (Access-Control-Allow-Origin Headers) or you need to use a CORS proxy.

API

You need to create a source, a cache and a seeder. When the script is served from the CouchDB and the tile source sends CORS headers (as osm.org does):

    var cache = new Seed.Cache.CouchDB('/seedjs/GoogleMapsCompatible-{TileMatrix}-{TileCol}-{TileRow}/tile');
    var source = new Seed.Source.WMTSSource('http://a.tile.openstreetmap.org/{TileMatrix}/{TileCol}/{TileRow}.png');
    var seeder = new Seed.Seeder({
        grid: new Seed.Grid(),
        bbox: new Seed.BBox(910447.65763357, 7006500.2326137, 917948.04103271, 7012529.2032187),
        levels: [0, 8]
    }, source, cache);

Start seeding with a custom callback that gets called after each seeded tile:

    seeder.start(function(progress) {
        console.log(progress.tiles + "/" + progress.totalTiles);
        if (progress.running == false) {
            console.log("finished!");
        }
    });

To let SeedJS use a CORS proxy for all external URLs:

    Seed.CORSProxyURL = 'http://localhost:8888/proxy/'
    var source = new Seed.Source.WMSSource('http://x.osm.omniscale.net/proxy/service?LAYERS=osm&' +
        'FORMAT=image%2Fpng&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&SRS=EPSG%3A900913&' +
        'BBOX={BBOX}&WIDTH=256&HEIGHT=256&tiled=true');
    var cache = new Seed.Cache.CouchDB('http://localhost:5984/seedjs/GoogleMapsCompatible-{TileMatrix}-{TileCol}-{TileRow}/tile');

Requests will then go to http://localhost:8888/proxy/http://x.osm.omniscale.net/proxy/service and http://localhost:8888/proxy/http://localhost:5984/seedjs/.

Interactive seeding

example/seed.html contains a simple OpenLayers client that demonstrates the SeedJS API.

Seeding on demand

example/offlinelayer contains CouchDB tile layers for OpenLayers and Leaflet that can use these seeded tiles. The layers can also fetch tiles that are missing in the CouchDB cache from a separate source layer. Loaded tiles are then stored in the CouchDB for future requests, so that the cache is building up as the user browses the map.