Despite your swelling pride, the blank screen is only so satisfying. Let’s add a visible layer. We’re going to use the Geography Class example from Mapbox and we’ll pull it locally, from device storage.
You’ll need to have done the globe or map tutorials, either is fine. Open your HelloEarth project and get ready.
If you haven’t got one here is a suitable ViewController (for Objective-C or Swift) file to start with. This version handles both a globe and a map and makes a nice starting point.
Geography Class MBTiles
We need the Geography Class MBTiles file from Mapbox. Luckily, you’ll can download the mbtiles file and add it to your project easily. (http://openstreetmap.org/)
First, download the [MBTile file] (https://s3.amazonaws.com/whirlyglobedocs/tutorialsupport/geography-class_medres.mbtiles) and save it into your projects directory.
Add geographyclass_medres.mbtiles to your project by dragging it into HelloEarth in your Project Navigator view. You can create a Resources folder there if you like, but it’s not necessary. The same goes for ‘Copy items into the destination group’s folder’ – if you want your project to have its own copy of the file, check that box. What you must do, however is check the ‘Add to targets’ box for HelloEarth, to ensure that the data is packaged with your app when it is built.
That will get the MBTiles file into the bundle. Next, we display it.
Adding a Layer
There are a few steps to displaying an MBTiles file on your globe or map.
Create the MaplyMBTileSource to read it.
Spin up a MaplyQuadImageTilesLayer to display it.
Start in a useful position on the globe
If you worked through the globe or the map example, you’ll need to add this little bit of code to your viewDidLoad method. This will make the examples work with either globe or map. If you’re using the ViewController file from above, you don’t need it.
Here’s how you open the MBTiles database, create the layer and add it to the globe or map. These changes go in the viewDidLoad method.
Now, when you run HelloEarth, you should see a colorful set of countries looking back at you.
If you’re doing a map it’ll look like that. Only, you know, flat.
You might notice there were two interesting objects there. First was the MaplyMBTileSource and the second a MaplyQuadImageTilesLayer.
The MaplyMBTileSource is responsible for reading the MBTiles file, which is just a big sqlite file with a bunch of images in it. The MaplyQuadImageTilesLayer is much more complicated. It responds to changes in viewer position and loads the most appropriate image tiles.
The MaplyQuadImageTilesLayer is pretty flexible. Let’s look at some of the properties.
handleEdges will add some extra geometry to ensure there’s no gap when mismatching levels of detail abut. You’ll never need this for a flat map, but for a globe or a 3D map, you might.
coverPoles will create ‘caps’ for the north and south poles. If you’re using a globe, and your projection doesn’t go all the way to the poles (this is common), you’ll want to turn this on.
drawPriority sets the priority of geometry created. You can use this to overlay image layers, with one caveat: it must be set immediately after the layer is created. You can’t change it later.
There are plenty of other properties we haven’t touched on here. Browse through the documentation and you’ll see a lot more.
Next up, an image layer you page over the network.