tilelive-streaming

A tilelive wrapper that transparently adds streaming functionality to providers.

About

This module adds createReadStream and createWriteStream methods to providers that support getTile and putTile respectively. Default functionality uses a tilelive.Scheme to generate a set of getTile requests, outputting a stream of streams containing tile data.

Usage

var tilelive = require("tilelive-streaming")(require("@mapbox/tilelive"), {
  concurrency: 8
});
require("@mapbox/mbtiles").registerProtocols(tilelive);

tilelive.load("mbtiles://./in.mbtiles", function(err, source) {
  return tilelive.load("mbtiles://./out.mbtiles", function(err, sink) {
    source.createReadStream().pipe(sink.createWriteStream());
  });
});

Options

createReadStream passes its options into a tilelive.Scheme subclass (specified by sourceConfig.scheme, defaulting to scanline), so the documentation for that takes precedence. In practice, minzoom, maxzoom, and bounds are likely candidates, as they can be used for filtering.

createWriteStream accepts an info option containing TileJSON. Its values will overwrite any info provided by the source (when appropriate).

Events

Writable streams will emit tile events (containing z, x, y, headers, and data properties) when data for a given tile has been fully received.

Readable streams will emit info events once it has been loaded (usually before tile data begins being sent).

Overriding Default Implementations

lib/ contains specific implementations for providers that do not (yet) support streaming natively and where the default behavior can be improved upon. mbtiles is a good example of this, as the actual list of tiles present can be determined directly from the source (rather than scanning a bounding box and zoom range for possible candidates).

MBTiles

mbtiles' createReadStream accepts a batchSize argument that allows the number of tiles read from the underlying SQLite3 database at a time to be specified.