Displaying offline map - load mbtiles file

[urossavelj]

Hi,

so after the previous issue with getting the extent of the visible map now I have another one. I loaded the visible tiles to a local sqlite db. I would now like to display the map from the tiles loaded for ex. when a button is clicked.

I tried like this but I get just an empty view

var tileSource = new MbTilesTileSource(new SQLiteConnectionString(Path.Combine(FileSystem.AppDataDirectory, "myOfflineDb.mbtiles")));

        _mapControl = new Mapsui.UI.Maui.MapControl();
        _mapControl.Map?.Layers.Add(new TileLayer(tileSource));

        Content = _mapControl;

I checked the myOfflineDb.mbtiles file with DB Browser for SQLite and it has the tiles inside, so that's ok. Is there anything else I have to set for it to display the tiles? What am I missing here?

[charlenni]

Do you moved around? Is there no tile at all?

[charlenni]

What @inforithmics asked is, did you while you display the offline tiles, you zoom in to zoom level 8 or higher? If you have zoom level 7 or lower, you will see nothing.

[urossavelj]

Ah, I understand what you meant now. I also tried zooming the map after I load the offline tiles, but it's still the same.

[inforithmics]

Is it necessary to use the MbTileCache? An alternative would be
https://github.com/Mapsui/Mapsui/blob/master/Mapsui.Extensions/Cache/SqlitePersistentCache.cs
SqlitePersitentCache from Mapsui Extensions. This can cache urls too beside of tiles but I don't know if it has an offical mbtile layout.

Have you tried to add your cached mbtile to qgis and display it there. To test if it works?

[urossavelj]

@inforithmics I tried also with this now, adding to db works also with this, but I can't use this code than, because the database it creates is missing the metadata table and I get an error:

        var tileSource = new MbTilesTileSource(new SQLiteConnectionString(Path.Combine(FileSystem.AppDataDirectory, "myOfflineDb.mbtiles.sqlite")));

        _mapControl = new Mapsui.UI.Maui.MapControl();
        _mapControl.Map?.Layers.Add(new TileLayer(tileSource));

How do I set the source than, is there another way if you use the SqlitePersistentCache from Mapsui.Extensions?

[urossavelj]

I also tried loading the mbtiles files in qgis and it also doesn't work, so if I have to guess the downlaoding from Mapsui/BruTiels is not working correctly

[charlenni]

Did you turn logging on as suggested, normally is the first answer to such a problem? Second would be, are you sure, that you create a valid MBTiles file? Do you add all tables? Are all the data in the files are correct? Do you update the field "bounds"?

To say, that a well tested file work, but your own file doesn't work on two different system is the fault of Mapsui is a little bit strange ;-)

[urossavelj]

Well, I used the code from MapsUI website and Brutile Github. It's not like I invented it and documentation for this things is almost non existent, this is also why I'm asking here for help to figure out why is it not working as I can't find a working example online.

If you check on Brutile Github, this is exactly what I'm doing: https://github.com/BruTile/BruTile:

Console.WriteLine("Show tile info");
foreach (var tileInfo in tileInfos)
{
    var tile = await tileSource.GetTileAsync(tileInfo);

    Console.WriteLine(
        $"tile col: {tileInfo.Index.Col}, " +
        $"tile row: {tileInfo.Index.Row}, " +
        $"tile level: {tileInfo.Index.Level} , " +
        $"tile size {tile.Length}");

      _cache.Add(tileInfo.Index, tile);
}

_cache is static SqlitePersistentCache _cache;
and than adding each fetched tile to sqlite.

Than for displaying this is the only thing I do:

        var tileSource = new MbTilesTileSource(new SQLiteConnectionString(Path.Combine(FileSystem.AppDataDirectory, "myOfflineDb.mbtiles.sqlite")));

        _mapControl = new Mapsui.UI.Maui.MapControl();
        _mapControl.Map?.Layers.Add(new TileLayer(tileSource));
            
        Content = _mapControl;

        _mapControl.Map.Navigator.ZoomToLevel(8);

By using SqlitePersistentCache cache and not MbTileCache, just the Tile table is created, no metadata. If I look at the "original" world.mbtiles file, the tables also have different names. Tile is called tiles and also additional metadata table(and also others). Can you tell me why the difference? If the "default" world.mbtiles file works I'm guessing that tiles, metadata is correct and not "Tile" table?

[charlenni]

I assume, that you expect something, that isn't provided. A MBTiles cache or SqlitePersistanceCache create not a valid MBTiles file according to the specification (see here). So, if you want to create a valid MBTiles file, you have to do this by your own. Use the same table names according to the specification and fill all fields correct.

And, last, but not least, read the copyrights of the most map providers, that don't allow saving tiles for offline use ;-)

[urossavelj]

Yeah, I read the terms :)

Ah, it makes sense than, I was sure it makes a valid db file.