osm_tile_fetcher

A Dart Implementation of Open Street Map Tile Fetcher.

This package is ready for download and use, check here.

purpose

This Dart package can be used for fetching tiles from Open Street Map Tile Server. You can select a certain area on Earth Surface and it fetches only those tiles required to cover that area.

It's lazy by default. And by lazy, I mean if you ask it fetch tiles for a certain zoom level and it finds those tiles are already present in certain directory, it won't simply fetch those files.

You can override this nature by setting lazy to false, while invoking tile fetcher method.

It also provides you a tile generation functionality, which will generate tiles for a certain zoom level. Tiles are identified by a tileId, which is composed of three elements.

  • Zoom Level
  • Row number in which Tile resides
  • Column number in which Tile resides

Above three elements are seperated by underscore ( _ ), and identifies a certain tile for a certain zoom level.

Tile generator can also give bound of certain tile i.e. the area which a certain tile covers.

Now let's use it.

usage

Lets say you want to generate all tiles for zoom level 2. This is how you can do so.

var tileGenerator = TileGenerator(2);

Gives you a list of tile identifiers.

tileGenerator.tilesWithOutExtent().forEach((tileId) => print(tileId));

If you want to get bounds of tiles too, try this one.

tileGenerator.tilesWithExtent().forEach((tileId, bounds) =>
    print('$tileId - $bounds'));

You may also query number of tiles required for a certain zoom level.

tileGenerator.tileCountInZoomLevel();

You'll be most likely using TileFetcher.

Let's fetch tiles for zoom level 2 and store them is current working directory.

var tileFetcher = TileFetcher(2, '.');

This API leverages power of Asynchronous Programming with Dart using Stream class.

So we'll fetch all tiles, which are required to cover BoundingBox(-180, 0, 0, 90).

Calling fetchTiles, will give us a Stream, and we listen to it for data. As soon as a certain tile is fetched, we'll receive its identifier in response. And when all tiles are fetched, Stream will be closed.

tileFetcher.fetchTiles(BoundingBox(-180, 0, 0, 90)).listen(
        (data) => print(data),
        cancelOnError: true,
        onDone: () => print('Done'),
        onError: (e) => print('Error: $e'),
      );

By default, fetchTiles is lazy i.e. it won't fetch a tile if it finds that tile in target directory.

Override this nature by putting lazy false.

tileFetcher.fetchTiles(BoundingBox(-180, 0, 0, 90), lazy: false).listen(
        (data) => print(data),
        cancelOnError: true,
        onDone: () => print('Done'),
        onError: (e) => print('Error: $e'),
      );

You might be interested in not giving any bounds, just call fetchTiles with null, which will lead to fetching all tiles required for covering whole world for that certain zoom level.

Using this for higher zoom level, is not recommened.

tileFetcher.fetchTiles(null).listen(
        (data) => print(data),
        cancelOnError: true,
        onDone: () => print('Done'),
        onError: (e) => print('Error: $e'),
      );

Always try fetching those tiles which are required for current viewport.

Sometimes, you may be interested in generating urls for a certain zoom level.

tileFetcher
      .urlGenerator(BoundingBox(-180, -90, 0, 0))
      .forEach((String url) => print(url));

If you don't want to cover any certain region i.e. cover whole Earth surface, just pass null, while invoking urlGenerator.

Above method gives you a list of urls, no usage of Stream here.

And last but not least, we've also a BoundingBox class, represent a certain area on surface of Earth, by using

  • minLongitude
  • minLatitude
  • maxLongitude
  • maxLatitude

It has a useful method, shouldFetchTile, helps you in taking decision whether you should fetch a tile or not. Tries to determine whether two bounding boxes are intersecting or not/ is second bounding box is contained with in first one or not.

BoundingBox(-180, -90, 180, 90)
        .shouldFetchTile(BoundingBox(-180, -90, 0, 0);

end

Well that's it. Hope it helps :)

And you may be interested in showing some <3 to this venture, by putting * on Github.

Libraries

osm_tile_fetcher