Add support for mbtiles 1.3 'center' metadata

CONFIGURATION.md

@@ -30,6 +30,7 @@ It also includes these global settings:
 * `compress` - whether to compress vector tiles (Any of "gzip","deflate" or "none"(default))
 * `name`, `version` and `description` - about your project (these are written into the MBTiles file)
 * `bounding_box` (optional) - the bounding box to output, in [minlon, minlat, maxlon, maxlat] order
+* `default_view` (optional) - the default location for the client to view, in [lon, lat, zoom] order (MBTiles only)
 * `mvt_version` (optional) - the version of the [Mapbox Vector Tile](https://github.com/mapbox/vector-tile-spec) spec to use; defaults to 2
 
 A typical config file would look like this:
@@ -81,6 +82,8 @@ This would combine the `roads` (z12-14) and `low_roads` (z9-11) layers into a si
 
 ### Additional metadata
 
+Tilemaker writes a `json` metadata field containing a `vector_layers` key, whose value is an array of JSON objects describing each layer and its attributes. This is part of the MBTiles 1.3 spec and required by certain clients.
+
 If you need to add additional metadata fields to your .mbtiles output, include the keys/values as an (optional) "metadata" entry under "settings". These will usually be string key/value pairs. (The value can also be another JSON entity - hash, array etc. - in which case it'll be encoded as JSON when written into the .mbtiles metadata table.)
 
 For example:

src/shared_data.cpp

@@ -8,6 +8,7 @@ class SharedData
 	int threadNum;
 	bool clippingBoxFromJSON;
 	double minLon, minLat, maxLon, maxLat;
+	string defaultView;
 	OSMObject osmObject;
 	OSMStore *osmStore;
 	bool includeID, compress, gzip;
@@ -58,6 +59,11 @@ class SharedData
 			clippingBox = Box(geom::make<Point>(minLon, lat2latp(minLat)),
 			                  geom::make<Point>(maxLon, lat2latp(maxLat)));
 		}
+		if (jsonConfig["settings"].HasMember("default_view")) {
+			defaultView = to_string(jsonConfig["settings"]["default_view"][0].GetDouble()) + "," +
+			              to_string(jsonConfig["settings"]["default_view"][1].GetDouble()) + "," +
+			              to_string(jsonConfig["settings"]["default_view"][2].GetInt());
+		}
 
 		// Check config is valid
 		if (endZoom > baseZoom) { cerr << "maxzoom must be the same or smaller than basezoom." << endl; exit (EXIT_FAILURE); }

src/tilemaker.cpp

@@ -433,6 +433,7 @@ int main(int argc, char* argv[]) {
 		sharedData.mbtiles.writeMetadata("bounds",bounds.str());
 		sharedData.mbtiles.writeMetadata("minzoom",to_string(sharedData.startZoom));
 		sharedData.mbtiles.writeMetadata("maxzoom",to_string(sharedData.endZoom));
+		if (!sharedData.defaultView.empty()) { sharedData.mbtiles.writeMetadata("center",sharedData.defaultView); }
 	}
 
 	// ----	Read all PBFs