使用本地磁贴的 TileProvider

问题描述

我想使用最新 Android Maps API (v2) 的新 TileProvider 功能在 GoogleMap 上叠加一些自定义图块.但是，由于我的用户很多时候都没有互联网，我想将图块存储在设备上的 zipfile/文件夹结构中.我将使用 Maptiler 和 geotiffs 生成我的图块.我的问题是:

I would like to use the new TileProvider functionality of the latest Android Maps API (v2) to overlay some custom tiles on the GoogleMap. However as my users will not have internet a lot of the time, I want to keep the tiles stored in a zipfile/folder structure on the device. I will be generating my tiles using Maptiler with geotiffs. My questions are:

1. 在设备上存储图块的最佳方式是什么?
2. 我将如何创建一个返回本地图块的 TileProvider?

推荐答案

1. 您可以将磁贴放入资产文件夹(如果应用程序大小可以接受)或在第一次启动时将其全部下载并放入设备存储(SD 卡)中.

1. You can put tiles into assets folder (if it is acceptable for the app size) or download them all on first start and put them into device storage (SD card).

您可以像这样实现 TileProvider:

You can implement TileProvider like this:

public class CustomMapTileProvider implements TileProvider {
    private static final int TILE_WIDTH = 256;
    private static final int TILE_HEIGHT = 256;
    private static final int BUFFER_SIZE = 16 * 1024;

    private AssetManager mAssets;

    public CustomMapTileProvider(AssetManager assets) {
        mAssets = assets;
    }

    @Override
    public Tile getTile(int x, int y, int zoom) {
        byte[] image = readTileImage(x, y, zoom);
        return image == null ? null : new Tile(TILE_WIDTH, TILE_HEIGHT, image);
    }

    private byte[] readTileImage(int x, int y, int zoom) {
        InputStream in = null;
        ByteArrayOutputStream buffer = null;

        try {
            in = mAssets.open(getTileFilename(x, y, zoom));
            buffer = new ByteArrayOutputStream();

            int nRead;
            byte[] data = new byte[BUFFER_SIZE];

            while ((nRead = in.read(data, 0, BUFFER_SIZE)) != -1) {
                buffer.write(data, 0, nRead);
            }
            buffer.flush();

            return buffer.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        } catch (OutOfMemoryError e) {
            e.printStackTrace();
            return null;
        } finally {
            if (in != null) try { in.close(); } catch (Exception ignored) {}
            if (buffer != null) try { buffer.close(); } catch (Exception ignored) {}
        }
    }

    private String getTileFilename(int x, int y, int zoom) {
        return "map/" + zoom + '/' + x + '/' + y + ".png";
    }
}

现在您可以将它与您的 GoogleMap 实例一起使用:

And now you can use it with your GoogleMap instance:

private void setUpMap() {
    mMap.setMapType(GoogleMap.MAP_TYPE_NONE);

    mMap.addTileOverlay(new TileOverlayOptions().tileProvider(new CustomMapTileProvider(getResources().getAssets())));

    CameraUpdate upd = CameraUpdateFactory.newLatLngZoom(new LatLng(LAT, LON), ZOOM);
    mMap.moveCamera(upd);
}

在我的例子中，我也遇到了 MapTiler 生成的瓦片的 y 坐标问题，但我通过将此方法添加到 CustomMapTileProvider 来管理它:

In my case I also had a problem with y coordinate of tiles generated by MapTiler, but I managed it by adding this method into CustomMapTileProvider:

/**
 * Fixing tile's y index (reversing order)
 */
private int fixYCoordinate(int y, int zoom) {
    int size = 1 << zoom; // size = 2^zoom
    return size - 1 - y;
}

并像这样从 getTile() 方法调用它:

and callig it from getTile() method like this:

@Override
public Tile getTile(int x, int y, int zoom) {
    y = fixYCoordinate(y, zoom);
    ...
}

[更新]

如果您知道自定义地图的精确区域，您应该为 getTile(...) 方法中的缺失图块返回 NO_TILE.

If you know exac area of your custom map, you should return NO_TILE for missing tiles from getTile(...) method.

我是这样做的:

private static final SparseArray<Rect> TILE_ZOOMS = new SparseArray<Rect>() {{
    put(8,  new Rect(135,  180,  135,  181 ));
    put(9,  new Rect(270,  361,  271,  363 ));
    put(10, new Rect(541,  723,  543,  726 ));
    put(11, new Rect(1082, 1447, 1086, 1452));
    put(12, new Rect(2165, 2894, 2172, 2905));
    put(13, new Rect(4330, 5789, 4345, 5810));
    put(14, new Rect(8661, 11578, 8691, 11621));
}};

@Override
public Tile getTile(int x, int y, int zoom) {
    y = fixYCoordinate(y, zoom);

    if (hasTile(x, y, zoom)) {
        byte[] image = readTileImage(x, y, zoom);
        return image == null ? null : new Tile(TILE_WIDTH, TILE_HEIGHT, image);
    } else {
        return NO_TILE;
    }
}

private boolean hasTile(int x, int y, int zoom) {
    Rect b = TILE_ZOOMS.get(zoom);
    return b == null ? false : (b.left <= x && x <= b.right && b.top <= y && y <= b.bottom);
}

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