2️⃣Prepare For Downloading

BaseRegions must be converted to DownloadableRegions before they can be used to download tiles.

These contain the original BaseRegion, but also some other information necessary for downloading, such as zoom levels and URL templates.

See this basic example:

final downloadable = region.toDownloadable(
    1, // Minimum Zoom
    18, // Maximum Zoom
    TileLayer(
        urlTemplate: '',
    ),
    // Additional Parameters
),

Additional Parameters

API Parameter	Type	Explanation	Default
parallelThreads	int	Number of download threads allowed to run simultaneously	10
preventRedownload	bool	Controls whether to skip downloading tiles that already exist	false
seaTileRemoval	bool	Controls whether to remove tiles that are entirely sea	false
start	int	Skip past a number of tiles 'at the start' of a region	0
end	int?	Skip a number of tiles 'at the end' of a region
crs	Crs	Map projection to use to calculate tiles	const Epsg3857()
errorHandler	void Function(Object?)?	Function to be called if a tile fails to download

Sea Tile Removal

By not storing pure tiles of sea, we can save a bunch of space on the user's device with every download. But how to do this?

Well, this package does it by analysing the bytes of the tile and checking if it's identical to a sample taken at lat/lng 0, 0 (Null Island) with zoom level 17. This tile should always be sea, and therefore any matching tile must also be sea.

In this way, we can delete tiles after we've checked them, if they are indeed sea. This method also means that tiles with ferry paths and other markings remain safe.

Sea Tile Removal does not reduce time or data consumption. Every tile must still be downloaded to check it.

Checking Number Of Tiles

Before downloading the region, you can count the number of tiles it will attempt to download. This is done by the check() method.

The method takes the DownloadableRegion generated above, and will return an int number of tiles. Note that this may take a while for large regions, as it is generating a list of all the tiles within the region.