如何通过将地图图块图像保存到 sqlite 数据库中来使用 osmdroid 实现离线地图？

发布于 2024-12-15 15:18:52 字数 132 浏览 0 评论 0 原文

我有一个项目也需要在离线模式下显示地图数据。我也使用过 OpenStreet 地图。我已经保存了地图图像（图块），每个图块都由数据库中的图块键引用。我想从数据库访问这些地图图块并相应地使用它们。

请建议我。

提前致谢。

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桃扇骨 2024-12-22 15:18:52

Osmdroid 中的地图图块由地图图块提供商提供。 Osmdroid 使用的默认图块提供程序是 MapTileProviderBasic。此提供程序扩展了 MapTileProviderArray ，这意味着它是几个其他图块提供程序的数组 - 当请求图块时，这些图块提供程序将被一一请求提供图块图像，直到其中一个提供为止。看一下 MapTileProviderBasic 的构造函数：

public MapTileProviderBasic(final IRegisterReceiver pRegisterReceiver,
              final INetworkAvailablityCheck aNetworkAvailablityCheck, 
                                        final ITileSource pTileSource) {

    super(pTileSource, pRegisterReceiver);    
    final TileWriter tileWriter = new TileWriter();

    final MapTileFilesystemProvider fileSystemProvider = 
        new MapTileFilesystemProvider(pRegisterReceiver, pTileSource);
    mTileProviderList.add(fileSystemProvider);

    final MapTileFileArchiveProvider archiveProvider = 
        new MapTileFileArchiveProvider(pRegisterReceiver, pTileSource);
    mTileProviderList.add(archiveProvider);

    final MapTileDownloader downloaderProvider = 
        new MapTileDownloader(pTileSource, tileWriter, aNetworkAvailablityCheck);
    mTileProviderList.add(downloaderProvider);
}

提供程序数组中添加了三个地图切片提供程序，按以下顺序：

MapTileFilesystemProvider - 提供来自文件系统（SD卡目录）
MapTileFileArchiveProvider - 提供来自文件系统中存档的图块
MapTileDownloader - 通过从互联网（例如从 OSM 服务器）下载图块来提供

图块MapTileProviderBasic 首先在文件系统中查找给定的图块，如果该图块不可用，则在存档文件中查找它，如果不可用，则再次从 Internet 下载该图块。

好的，这是默认机制。如果您想更改此机制以查找存储在数据库中的图块，那么您可以创建自己的类似于 MapTileProviderBasic 的类。因此，您的类也可以扩展 MapTileProviderArray 并仅在构造函数中使用其他提供程序。在Osmdroid中有一个类DatabaseFileArchive 它可能可以帮助您从数据库中读取图块。

创建您自己的图块提供程序后，您应该使用它而不是默认的提供程序。地图图块提供程序附加到MapView。 MapView 的某些构造函数将 MapTileProviderBase 作为参数 - 您可以使用其中之一来附加您自己的提供程序。

Map tiles in Osmdroid are provided by map tile providers. The default tile provider used by Osmdroid is MapTileProviderBasic. This provider extends MapTileProviderArray, which means that it is an array of a few other tile providers - when a tile is requested these tile providers are asked one by one for a tile image until one of them provides it. Take a look at the constructor of MapTileProviderBasic:

public MapTileProviderBasic(final IRegisterReceiver pRegisterReceiver,
              final INetworkAvailablityCheck aNetworkAvailablityCheck, 
                                        final ITileSource pTileSource) {

    super(pTileSource, pRegisterReceiver);    
    final TileWriter tileWriter = new TileWriter();

    final MapTileFilesystemProvider fileSystemProvider = 
        new MapTileFilesystemProvider(pRegisterReceiver, pTileSource);
    mTileProviderList.add(fileSystemProvider);

    final MapTileFileArchiveProvider archiveProvider = 
        new MapTileFileArchiveProvider(pRegisterReceiver, pTileSource);
    mTileProviderList.add(archiveProvider);

    final MapTileDownloader downloaderProvider = 
        new MapTileDownloader(pTileSource, tileWriter, aNetworkAvailablityCheck);
    mTileProviderList.add(downloaderProvider);
}

There are three map tile providers added to the array of providers, in this order:

MapTileFilesystemProvider - provides tiles from the file system (SD card directory)
MapTileFileArchiveProvider - provides tiles from archive in file system
MapTileDownloader - provides tiles by downloading them from the Internet (e.g. from OSM servers)

So the MapTileProviderBasic looks for a given tile first in the file system, if the tile is not available then it looks for it in archive files and again if it is not available there it downloads the tile from the Internet.

Ok, this is the default mechanism. If you want to change this mechanism to look for tiles stored in a DB then you can create you own class similar to MapTileProviderBasic. So your class could also extend MapTileProviderArray and just use other providers in the constructor. In Osmdroid there is a class DatabaseFileArchive which could probably help you in reading tiles from the DB.

After creating your own tile provider you should use it instead of the default one. Map tile providers are attached to the MapView. Some of the constructors of MapView take MapTileProviderBase as an argument - you can use one of them to attach your own provider.