GIS的学习（四十二）osmdroid基于离线地图的几种格式
在osmdroid中支持多种离线地图格式，其中sqlite，mbtiles，zip，gemf等格式，那么他们的格式有什么不同呢？
下面我们慢慢来研究一下源代码既可以知道。
针对ArchiveFileFactory的类查看如下：
package org.osmdroid.tileprovider.modules;
import java.io.File;
import java.io.IOException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import android.database.sqlite.SQLiteException;
public class ArchiveFileFactory {
private static final Logger logger = LoggerFactory.getLogger(ArchiveFileFactory.class);
/**
* Return an implementation of {@link IArchiveFile} for the specified file.
* @return an implementation, or null if there's no suitable implementation
*/
public static IArchiveFile getArchiveFile(final File pFile) {
if (pFile.getName().endsWith(".zip")) {
try {
return ZipFileArchive.getZipFileArchive(pFile);
} catch (final IOException e) {
logger.error("Error opening ZIP file", e);
}
}
if (pFile.getName().endsWith(".sqlite")) {
try {
return DatabaseFileArchive.getDatabaseFileArchive(pFile);
} catch (final SQLiteException e) {
logger.error("Error opening SQL file", e);
}
}
if (pFile.getName().endsWith(".mbtiles")) {
try {
return MBTilesFileArchive.getDatabaseFileArchive(pFile);
} catch (final SQLiteException e) {
logger.error("Error opening MBTiles SQLite file", e);
}
}
if (pFile.getName().endsWith(".gemf")) {
try {
return GEMFFileArchive.getGEMFFileArchive(pFile);
} catch (final IOException e) {
logger.error("Error opening GEMF file", e);
}
}
return null;
}
}
其中sqlite格式如下：存储的表名为：tiles字段为tile，key,provider,
具体实现如下：
package org.osmdroid.tileprovider.modules;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.InputStream;
import org.osmdroid.tileprovider.MapTile;
import org.osmdroid.tileprovider.tilesource.ITileSource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
public class DatabaseFileArchive implements IArchiveFile {
private static final Logger logger = LoggerFactory.getLogger(DatabaseFileArchive.class);
private final SQLiteDatabase mDatabase;
private DatabaseFileArchive(final SQLiteDatabase pDatabase) {
mDatabase = pDatabase;
}
public static DatabaseFileArchive getDatabaseFileArchive(final File pFile) throws SQLiteException {
return new DatabaseFileArchive(SQLiteDatabase.openOrCreateDatabase(pFile, null));
}
@Override
public InputStream getInputStream(final ITileSource pTileSource, final MapTile pTile) {
try {
InputStream ret = null;
final String[] tile = {"tile"};
final long x = (long) pTile.getX();
final long y = (long) pTile.getY();
final long z = (long) pTile.getZoomLevel();
final long index = ((z << z) + x << z) + y;
final Cursor cur = mDatabase.query("tiles", tile, "key = " + index + " and provider = '" + pTileSource.name() + "'", null, null, null, null);
if(cur.getCount() != 0) {
cur.moveToFirst();
ret = new ByteArrayInputStream(cur.getBlob(0));
}
cur.close();
if(ret != null) {
return ret;
}
} catch(final Throwable e) {
logger.warn("Error getting db stream: " + pTile, e);
}
return null;
}
@Override
public String toString() {
return "DatabaseFileArchive [mDatabase=" + mDatabase.getPath() + "]";
}
}
格式为mbtiles的数据结构：
// TABLE tiles (zoom_level INTEGER, tile_column INTEGER, tile_row INTEGER, tile_data BLOB); public final static String TABLE_TILES = "tiles"; public final static String COL_TILES_ZOOM_LEVEL = "zoom_level"; public final static String COL_TILES_TILE_COLUMN = "tile_column"; public final static String COL_TILES_TILE_ROW = "tile_row"; public final static String COL_TILES_TILE_DATA = "tile_data";
具体实现：
package org.osmdroid.tileprovider.modules;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.InputStream;
import org.osmdroid.tileprovider.MapTile;
import org.osmdroid.tileprovider.tilesource.ITileSource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
public class MBTilesFileArchive implements IArchiveFile {
private static final Logger logger = LoggerFactory.getLogger(MBTilesFileArchive.class);
private final SQLiteDatabase mDatabase;
// TABLE tiles (zoom_level INTEGER, tile_column INTEGER, tile_row INTEGER, tile_data BLOB);
public final static String TABLE_TILES = "tiles";
public final static String COL_TILES_ZOOM_LEVEL = "zoom_level";
public final static String COL_TILES_TILE_COLUMN = "tile_column";
public final static String COL_TILES_TILE_ROW = "tile_row";
public final static String COL_TILES_TILE_DATA = "tile_data";
private MBTilesFileArchive(final SQLiteDatabase pDatabase) {
mDatabase = pDatabase;
}
public static MBTilesFileArchive getDatabaseFileArchive(final File pFile) throws SQLiteException {
return new MBTilesFileArchive(
SQLiteDatabase.openDatabase(
pFile.getAbsolutePath(),
null,
SQLiteDatabase.NO_LOCALIZED_COLLATORS | SQLiteDatabase.OPEN_READONLY));
}
@Override
public InputStream getInputStream(final ITileSource pTileSource, final MapTile pTile) {
try {
InputStream ret = null;
final String[] tile = { COL_TILES_TILE_DATA };
final String[] xyz = {
Integer.toString(pTile.getX())
, Double.toString(Math.pow(2, pTile.getZoomLevel()) - pTile.getY() - 1) // Use Google Tiling Spec
, Integer.toString(pTile.getZoomLevel())
};
final Cursor cur = mDatabase.query(TABLE_TILES, tile, "tile_column=? and tile_row=? and zoom_level=?", xyz, null, null, null);
if(cur.getCount() != 0) {
cur.moveToFirst();
ret = new ByteArrayInputStream(cur.getBlob(0));
}
cur.close();
if(ret != null) {
return ret;
}
} catch(final Throwable e) {
logger.warn("Error getting db stream: " + pTile, e);
}
return null;
}
@Override
public String toString() {
return "DatabaseFileArchive [mDatabase=" + mDatabase.getPath() + "]";
}
}
GEMF文件格式的：
GEMF格式的文件存储算法比较复杂，但是据说为加载最快的方式。
package org.osmdroid.tileprovider.modules;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import org.osmdroid.tileprovider.MapTile;
import org.osmdroid.tileprovider.tilesource.ITileSource;
import org.osmdroid.util.GEMFFile;
public class GEMFFileArchive implements IArchiveFile {
private final GEMFFile mFile;
private GEMFFileArchive(final File pFile) throws FileNotFoundException, IOException {
mFile = new GEMFFile(pFile);
}
public static GEMFFileArchive getGEMFFileArchive(final File pFile) throws FileNotFoundException, IOException {
return new GEMFFileArchive(pFile);
}
@Override
public InputStream getInputStream(final ITileSource pTileSource, final MapTile pTile) {
return mFile.getInputStream(pTile.getX(), pTile.getY(), pTile.getZoomLevel());
}
@Override
public String toString() {
return "GEMFFileArchive [mGEMFFile=" + mFile.getName() + "]";
}
}
ZIP格式：
package org.osmdroid.tileprovider.modules;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.ZipEntry;
import java.util.zip.ZipException;
import java.util.zip.ZipFile;
import org.osmdroid.tileprovider.MapTile;
import org.osmdroid.tileprovider.tilesource.ITileSource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class ZipFileArchive implements IArchiveFile {
private static final Logger logger = LoggerFactory.getLogger(ZipFileArchive.class);
private final ZipFile mZipFile;
private ZipFileArchive(final ZipFile pZipFile) {
mZipFile = pZipFile;
}
public static ZipFileArchive getZipFileArchive(final File pFile) throws ZipException, IOException {
return new ZipFileArchive(new ZipFile(pFile));
}
@Override
public InputStream getInputStream(final ITileSource pTileSource, final MapTile pTile) {
final String path = pTileSource.getTileRelativeFilenameString(pTile);
try {
final ZipEntry entry = mZipFile.getEntry(path);
if (entry != null) {
return mZipFile.getInputStream(entry);
}
} catch (final IOException e) {
logger.warn("Error getting zip stream: " + pTile, e);
}
return null;
}
@Override
public String toString() {
return "ZipFileArchive [mZipFile=" + mZipFile.getName() + "]";
}
}
实现：最初显示”中国地图（省界）“，放大到一定程度显示”中国地图（地市分界）“，继续放大切换到Google街道地图。
<!DOCTYPE html>
<html>
<head>
<title>中国地图</title>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<link rel="stylesheet" href="css/style.css" type="text/css" />
<style type="text/css" media="screen">
body {
margin:0;
padding:0;
height:100%;
}
.bigmap {
position:absolute;
left:0;
top:0px;
padding:0;
width:100%;
height:100%;
border:1px solid #333;
}
</style>
<script type="text/javascript" src="js/OpenLayers/lib/OpenLayers.js"></script>
<script src="http://maps.google.com/maps/api/js?v=3.6&sensor=false"></script>
<script type="text/javascript">
var map, layer_province, layer_city, layer_street, vlayer;
// 第一次打开地图的中心位置（经度、纬度）
var firstLon = 109.33981;
var firstLat = 33.72419;
/*
* 切换地图比例尺设置
* scale1：
* scale2: 省地图和地市地图切换点
* scale3: 地市地图和谷歌街道地图切换点
*/
var scale1 = 20000000;
var scale2 = 10000000;
var scale3 = 2000000;
var level1 = 1;
var level2 = 2;
var level3 = 3;
var level = level1;
function init() {
// 创建MAP DIV框架
map = new OpenLayers.Map("map",
{
maxResolution: 'auto',
maxExtent: new OpenLayers.Bounds(
73.44696044921875, 6.318641185760498,
135.08583068847656, 53.557926177978516),
displayProjection: new OpenLayers.Projection("EPSG:4326")
});
// 增加中国地图(省界) Layer
addProvinceLayer()
// 增加中国地图(地市分界) Layer
addCityLayer();
// 增加Google Street Layer
addStreetLayer();
// 增加地图Layer切换Register
addMapRegister();
map.zoomToMaxExtent();
map.setCenter(new OpenLayers.LonLat(firstLon, firstLat), 0);
map.addControl(new OpenLayers.Control.Scale());
map.addControl(new OpenLayers.Control.MousePosition());
map.addControl(new OpenLayers.Control.LayerSwitcher());
}
function addProvinceLayer() {
layer_province = new OpenLayers.Layer.WMS(
"China:province", "http://10.0.0.239:8081/geoserver/wms",
{
layers: "China:province",
},
{
singleTile: true, //set single label
isBaseLayer: true,
projection: "EPSG:4326",
maxExtent: new OpenLayers.Bounds(
73.44696044921875, 6.318641185760498,
135.08583068847656, 53.557926177978516)
}
);
map.addLayer(layer_province);
}
function addCityLayer() {
layer_city = new OpenLayers.Layer.WMS(
"China:city", "http://10.0.0.239:8081/geoserver/wms",
{
layers: "China:city"
},
{
singleTile: true, //set single label
visibility: false,
projection: "EPSG:4326",
displayInLayerSwitcher: false,
maxExtent: new OpenLayers.Bounds(
73.44696044921875, 6.318641185760498,
135.08583068847656, 53.557926177978516)
}
);
map.addLayer(layer_city);
}
function addStreetLayer() {
layer_street = new OpenLayers.Layer.Google(
"Google Streets", // the default
{
numZoomLevels: 18 ,
projection: "EPSG:900913",
visibility: false,
displayInLayerSwitcher: false,
maxExtent: new OpenLayers.Bounds(
-128 * 156543.03390625,
-128 * 156543.03390625,
128 * 156543.03390625,
128 * 156543.03390625)
}
);
map.addLayer(layer_street);
}
function addMapRegister(){
map.events.register("zoomend", map, function(){
var cur_scale = map.getScale();
if(cur_scale >= scale2) {
if(level != level1) {
if(level == level2) {
map.setCenter(map.center.transform(
new OpenLayers.Projection("EPSG:4326"),
new OpenLayers.Projection("EPSG:4326")
), map.getZoom());
} else {
map.setCenter(map.center.transform(
new OpenLayers.Projection("EPSG:900913"),
new OpenLayers.Projection("EPSG:4326")
), map.getZoom());
}
level = level1;
layer_province.displayInLayerSwitcher = true;
layer_city.displayInLayerSwitcher = false;
layer_street.displayInLayerSwitcher = false;
map.setBaseLayer(layer_province);
layer_city.setVisibility(false);
layer_street.setVisibility(false);
}
} else if(cur_scale < scale2 && cur_scale >= scale3){
if(level != level2){
if(level == level1) {
map.setCenter(map.center.transform(
new OpenLayers.Projection("EPSG:4326"),
new OpenLayers.Projection("EPSG:4326")
), map.getZoom());
} else {
map.setCenter(map.center.transform(
new OpenLayers.Projection("EPSG:900913"),
new OpenLayers.Projection("EPSG:4326")
), map.getZoom());
}
level = level2;
layer_province.displayInLayerSwitcher = false;
layer_city.displayInLayerSwitcher = true;
layer_street.displayInLayerSwitcher = false;
map.setBaseLayer(layer_city);
layer_province.setVisibility(false);
layer_street.setVisibility(false);
}
} else if(cur_scale < scale3){
if(level != level3) {
map.setCenter(map.center.transform(
new OpenLayers.Projection("EPSG:4326"),
new OpenLayers.Projection("EPSG:900913")
), map.getZoom());
level = level3;
layer_province.displayInLayerSwitcher = false;
layer_city.displayInLayerSwitcher = false;
layer_street.displayInLayerSwitcher = true;
map.setBaseLayer(layer_street);
layer_city.setVisibility(false);
layer_province.setVisibility(false);
}
}
});
}
</script>
</head>
<body onload="init()" >
<div id="map" class="bigmap"></div>
</body>
</html>
参考：