前文提供中国电子地图校正精确校正数据免费下载 提供了用于校正中国地图偏移的数据，下需给出如何利用这些数据来校正地图偏移的算法代码。
这个校正适用于 Google map China, Microsoft map china ,MapABC 等，因为这些地图构成方法是一样的。
有兴趣的可以参见 http://www./forum/vi ... &extra=page%3D1
具体原理这里不详细说，有兴趣的可以参见后续有关 Mapdigit 地图开发包教程或是 http://www./gis.php 中开发指南。
关于校正精度的问题，0.01的数据相邻两个记录差最大在5个点左右，对应于18级每点代表0.5972米，也就是校正好误差在3米以内，而GPS接收器本身误差也在5米左右，比0.01再高的数据已无多大实际意义。5M以内对于精确定位及导航已足够，特别是对于导航时一般还会同时使用路径匹配算法，可以将位置精确校正路径上。
第一部分代码来自 http://msdn.microsoft.com/en-us/library/bb259689.aspx
第二部分代码为校正算法，算法很简单
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace MapDigit.GIS
{
public class GeoLatLng
{
public GeoLatLng(double latitude, double longitude)
{
this.latitude = latitude;
this.longitude = longitude;
}
public double latitude;
public double longitude;
}
public class GeoPoint
{
public GeoPoint(int x, int y)
{
this.x = x;
this.y = y;
}
public int x;
public int y;
}
public class OffsetInChina
{
//用于从GPS坐标转换为偏移后坐标
public static GeoLatLng fromEarthToMars(GeoLatLng earth)
{
GeoPoint ptOffset = getOffset(earth.latitude, earth.longitude);
if (ptOffset.x != 0 || ptOffset.y != 0)
{
int pixelX, pixelY;
TileSystem.LatLongToPixelXY(earth.latitude, earth.longitude, 18, out pixelX, out pixelY);
GeoPoint pt = new GeoPoint(pixelX, pixelY);
pt.x += ptOffset.x;
pt.y += ptOffset.y;
double latitude, longitude;
TileSystem.PixelXYToLatLong(pt.x, pt.y, 18, out latitude, out longitude);
return new GeoLatLng(latitude, longitude);
}
else
{
return new GeoLatLng(earth.latitude, earth.longitude);
}
}
//用于将偏移后坐标转成真实的坐标
public static GeoLatLng fromMarToEarth(GeoLatLng mars)
{
GeoPoint ptOffset = getOffset(mars.latitude, mars.longitude);
if (ptOffset.x != 0 || ptOffset.y != 0)
{
int pixelX, pixelY;
TileSystem.LatLongToPixelXY(mars.latitude, mars.longitude, 18, out pixelX, out pixelY);
GeoPoint pt = new GeoPoint(pixelX, pixelY);
pt.x -= ptOffset.x;
pt.y -= ptOffset.y;
double latitude, longitude;
TileSystem.PixelXYToLatLong(pt.x, pt.y, 18, out latitude, out longitude);
return new GeoLatLng(latitude, longitude);
}
else
{
return new GeoLatLng(mars.latitude, mars.longitude);
}
}
//这个函数用于将需要查询的经纬度转成最近的0.01分度值，无插值
//也可以自行实现插值
private static GeoPoint getQueryLocation(double latitude, double longitude)
{
int lat = (int)(latitude * 100);
int lng = (int)(longitude * 100);
double lat1 = ((int)(latitude * 1000 + 0.499999)) / 10.0;
double lng1 = ((int)(longitude * 1000 + 0.499999)) / 10.0;
for (double x = longitude; x < longitude + 1; x += 0.5)
{
for (double y = latitude; x < latitude + 1; y += 0.5)
{
if (x <= lng1 && lng1 < (x + 0.5) && lat1 >= y && lat1 < (y + 0.5))
{
return new GeoPoint((int)(x + 0.5), (int)(y + 0.5));
}
}
}
return new GeoPoint(lng, lat);
}
private static GeoPoint getOffset(double longitude, double latitude)
{
//这个函数用于返回查询结果，就是从校正数据中返回18级时x,y方偏移
//可以自行实现
return null;
}
}
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace MapDigit.GIS
{
public class GeoLatLng
{
public GeoLatLng(double latitude, double longitude)
{
this.latitude = latitude;
this.longitude = longitude;
}
public double latitude;
public double longitude;
}
public class GeoPoint
{
public GeoPoint(int x, int y)
{
this.x = x;
this.y = y;
}
public int x;
public int y;
}
public class OffsetInChina
{
//用于从GPS坐标转换为偏移后坐标
public static GeoLatLng fromEarthToMars(GeoLatLng earth)
{
GeoPoint ptOffset = getOffset(earth.latitude, earth.longitude);
if (ptOffset.x != 0 || ptOffset.y != 0)
{
int pixelX, pixelY;
TileSystem.LatLongToPixelXY(earth.latitude, earth.longitude, 18, out pixelX, out pixelY);
GeoPoint pt = new GeoPoint(pixelX, pixelY);
pt.x += ptOffset.x;
pt.y += ptOffset.y;
double latitude, longitude;
TileSystem.PixelXYToLatLong(pt.x, pt.y, 18, out latitude, out longitude);
return new GeoLatLng(latitude, longitude);
}
else
{
return new GeoLatLng(earth.latitude, earth.longitude);
}
}
//用于将偏移后坐标转成真实的坐标
public static GeoLatLng fromMarToEarth(GeoLatLng mars)
{
GeoPoint ptOffset = getOffset(mars.latitude, mars.longitude);
if (ptOffset.x != 0 || ptOffset.y != 0)
{
int pixelX, pixelY;
TileSystem.LatLongToPixelXY(mars.latitude, mars.longitude, 18, out pixelX, out pixelY);
GeoPoint pt = new GeoPoint(pixelX, pixelY);
pt.x -= ptOffset.x;
pt.y -= ptOffset.y;
double latitude, longitude;
TileSystem.PixelXYToLatLong(pt.x, pt.y, 18, out latitude, out longitude);
return new GeoLatLng(latitude, longitude);
}
else
{
return new GeoLatLng(mars.latitude, mars.longitude);
}
}
//这个函数用于将需要查询的经纬度转成最近的0.01分度值，无插值
//也可以自行实现插值
private static GeoPoint getQueryLocation(double latitude, double longitude)
{
int lat = (int)(latitude * 100);
int lng = (int)(longitude * 100);
double lat1 = ((int)(latitude * 1000 + 0.499999)) / 10.0;
double lng1 = ((int)(longitude * 1000 + 0.499999)) / 10.0;
for (double x = longitude; x < longitude + 1; x += 0.5)
{
for (double y = latitude; x < latitude + 1; y += 0.5)
{
if (x <= lng1 && lng1 < (x + 0.5) && lat1 >= y && lat1 < (y + 0.5))
{
return new GeoPoint((int)(x + 0.5), (int)(y + 0.5));
}
}
}
return new GeoPoint(lng, lat);
}
private static GeoPoint getOffset(double longitude, double latitude)
{
//这个函数用于返回查询结果，就是从校正数据中返回18级时x,y方偏移
//可以自行实现
return null;
}
}
}
其中需自已实现的是private static GeoPoint getOffset(double longitude, double latitude)
就是从下载的数据中，根据经纬度查出对应的X,Y向偏差。
附第一部分代码，
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using System;
using System.Text;
namespace MapDigit.GIS
{
static class TileSystem
{
private const double EARTH_RADIUS = 6378137;
private const double MIN_LATITUDE = -85.05112878;
private const double MAX_LATITUDE = 85.05112878;
private const double MIN_LONGITUDE = -180;
private const double MAX_LONGITUDE = 180;
/// <summary>
/// Clips a number to the specified minimum and maximum values.
/// </summary>
/// <param name="n">The number to clip.</param>
/// <param name="minValue">Minimum allowable value.</param>
/// <param name="maxValue">Maximum allowable value.</param>
/// <returns>The clipped value.</returns>
private static double Clip(double n, double minValue, double maxValue)
{
return Math.Min(Math.Max(n, minValue), maxValue);
}
/// <summary>
/// Determines the map width and height (in pixels) at a specified level
/// of detail.
/// </summary>
/// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)
/// to 23 (highest detail).</param>
/// <returns>The map width and height in pixels.</returns>
public static uint MapSize(int levelOfDetail)
{
return (uint)256 << levelOfDetail;
}
/// <summary>
/// Determines the ground resolution (in meters per pixel) at a specified
/// latitude and level of detail.
/// </summary>
/// <param name="latitude">Latitude (in degrees) at which to measure the
/// ground resolution.</param>
/// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)
/// to 23 (highest detail).</param>
/// <returns>The ground resolution, in meters per pixel.</returns>
public static double GroundResolution(double latitude, int levelOfDetail)
{
latitude = Clip(latitude, MIN_LATITUDE, MAX_LATITUDE);
return Math.Cos(latitude * Math.PI / 180) * 2 * Math.PI * EARTH_RADIUS / MapSize(levelOfDetail);
}
/// <summary>
/// Determines the map scale at a specified latitude, level of detail,
/// and screen resolution.
/// </summary>
/// <param name="latitude">Latitude (in degrees) at which to measure the
/// map scale.</param>
/// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)
/// to 23 (highest detail).</param>
/// <param name="screenDpi">Resolution of the screen, in dots per inch.</param>
/// <returns>The map scale, expressed as the denominator N of the ratio 1 : N.</returns>
public static double MapScale(double latitude, int levelOfDetail, int screenDpi)
{
return GroundResolution(latitude, levelOfDetail) * screenDpi / 0.0254;
}
/// <summary>
/// Converts a point from latitude/longitude WGS-84 coordinates (in degrees)
/// into pixel XY coordinates at a specified level of detail.
/// </summary>
/// <param name="latitude">Latitude of the point, in degrees.</param>
/// <param name="longitude">Longitude of the point, in degrees.</param>
/// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)
/// to 23 (highest detail).</param>
/// <param name="pixelX">Output parameter receiving the X coordinate in pixels.</param>
/// <param name="pixelY">Output parameter receiving the Y coordinate in pixels.</param>
public static void LatLongToPixelXY(double latitude, double longitude, int levelOfDetail, out int pixelX, out int pixelY)
{
latitude = Clip(latitude, MIN_LATITUDE, MAX_LATITUDE);
longitude = Clip(longitude, MIN_LONGITUDE, MAX_LONGITUDE);
double x = (longitude + 180) / 360;
double sinLatitude = Math.Sin(latitude * Math.PI / 180);
double y = 0.5 - Math.Log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI);
uint mapSize = MapSize(levelOfDetail);
pixelX = (int)Clip(x * mapSize + 0.5, 0, mapSize - 1);
pixelY = (int)Clip(y * mapSize + 0.5, 0, mapSize - 1);
}
/// <summary>
/// Converts a pixel from pixel XY coordinates at a specified level of detail
/// into latitude/longitude WGS-84 coordinates (in degrees).
/// </summary>
/// <param name="pixelX">X coordinate of the point, in pixels.</param>
/// <param name="pixelY">Y coordinates of the point, in pixels.</param>
/// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)
/// to 23 (highest detail).</param>
/// <param name="latitude">Output parameter receiving the latitude in degrees.</param>
/// <param name="longitude">Output parameter receiving the longitude in degrees.</param>
public static void PixelXYToLatLong(int pixelX, int pixelY, int levelOfDetail, out double latitude, out double longitude)
{
double mapSize = MapSize(levelOfDetail);
double x = (Clip(pixelX, 0, mapSize - 1) / mapSize) - 0.5;
double y = 0.5 - (Clip(pixelY, 0, mapSize - 1) / mapSize);
latitude = 90 - 360 * Math.Atan(Math.Exp(-y * 2 * Math.PI)) / Math.PI;
longitude = 360 * x;
}
/// <summary>
/// Converts pixel XY coordinates into tile XY coordinates of the tile containing
/// the specified pixel.
/// </summary>
/// <param name="pixelX">Pixel X coordinate.</param>
/// <param name="pixelY">Pixel Y coordinate.</param>
/// <param name="tileX">Output parameter receiving the tile X coordinate.</param>
/// <param name="tileY">Output parameter receiving the tile Y coordinate.</param>
public static void PixelXYToTileXY(int pixelX, int pixelY, out int tileX, out int tileY)
{
tileX = pixelX / 256;
tileY = pixelY / 256;
}
/// <summary>
/// Converts tile XY coordinates into pixel XY coordinates of the upper-left pixel
/// of the specified tile.
/// </summary>
/// <param name="tileX">Tile X coordinate.</param>
/// <param name="tileY">Tile Y coordinate.</param>
/// <param name="pixelX">Output parameter receiving the pixel X coordinate.</param>
/// <param name="pixelY">Output parameter receiving the pixel Y coordinate.</param>
public static void TileXYToPixelXY(int tileX, int tileY, out int pixelX, out int pixelY)
{
pixelX = tileX * 256;
pixelY = tileY * 256;
}
/// <summary>
/// Converts tile XY coordinates into a QuadKey at a specified level of detail.
/// </summary>
/// <param name="tileX">Tile X coordinate.</param>
/// <param name="tileY">Tile Y coordinate.</param>
/// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)
/// to 23 (highest detail).</param>
/// <returns>A string containing the QuadKey.</returns>
public static string TileXYToQuadKey(int tileX, int tileY, int levelOfDetail)
{
StringBuilder quadKey = new StringBuilder();
for (int i = levelOfDetail; i > 0; i--)
{
char digit = '0';
int mask = 1 << (i - 1);
if ((tileX & mask) != 0)
{
digit++;
}
if ((tileY & mask) != 0)
{
digit++;
digit++;
}
quadKey.Append(digit);
}
return quadKey.ToString();
}
/// <summary>
/// Converts a QuadKey into tile XY coordinates.
/// </summary>
/// <param name="quadKey">QuadKey of the tile.</param>
/// <param name="tileX">Output parameter receiving the tile X coordinate.</param>
/// <param name="tileY">Output parameter receiving the tile Y coordinate.</param>
/// <param name="levelOfDetail">Output parameter receiving the level of detail.</param>
public static void QuadKeyToTileXY(string quadKey, out int tileX, out int tileY, out int levelOfDetail)
{
tileX = tileY = 0;
levelOfDetail = quadKey.Length;
for (int i = levelOfDetail; i > 0; i--)
{
int mask = 1 << (i - 1);
switch (quadKey[levelOfDetail - i])
{
case '0':
break;
case '1':
tileX |= mask;
break;
case '2':
tileY |= mask;
break;
case '3':
tileX |= mask;
tileY |= mask;
break;
default:
throw new ArgumentException("Invalid QuadKey digit sequence.");
}
}
} | |
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