在这方面,我要做的是:

回答。 措施a(这是有待改进的任意价值) 周围的面积为2千米,并具有东西/北/南界限的数值。

对该广场内的分子提出质询。 这是一件轻而易举的事,你刚才不得不这样做。

select * from points where lat between ? and ? and lon between ? and ?

取得你的结果。 成果不够(显然不到5项,但我要说的是,有两倍是肯定的)。 太多(即100多个),再次尝试少半径。

Once you have enough, load them, make sure all 5 elements you need are not only in the Xkm wide square, but also in the Xkm radius circle (to avoid having a potential closer element not detected by the previous approximation).

Another approach

只有在您的某一点与你所寻求的点相对接近时,才会有效。

测量一个平地的面积。 在接近你的时候,你可以考虑一下相对、lon和距离之间的直线关系。 这使你能够提出简单限定的请求。 (倍增和增)。 同样,为了在“四方”要求之后进行适当的计算,选择了一点点。

在您的表格中插入 co_lat_rad,sin_lat_rad,cos_lon_rad,sin_lon_rad

contentValues.put("cos_lat_rad", Math.cos(deg2rad(latitude)));
contentValues.put("sin_lat_rad", Math.sin(deg2rad(latitude)));
contentValues.put("cos_lon_rad", Math.cos(deg2rad(longitude)));
contentValues.put("sin_lon_rad", Math.sin(deg2rad(longitude)));

学历

public static double deg2rad(double deg) {
    return (deg * Math.PI / 180.0);
}

问 题,距离

 Cursor c=database.dis(String.valueOf(Math.cos((double) distance / (double) 6380)), Math.cos(deg2rad(latitude)), Math.sin(deg2rad(latitude)), Math.cos(deg2rad(longitude)), Math.sin(deg2rad(longitude)));

问 题

public Cursor dis(String dis, double cos_lat_rad, double sin_lat_rad, double cos_lon_rad, double sin_lon_rad) {

    Cursor cursor = sqLiteDatabase.rawQuery("SELECT * ,(" + sin_lat_rad + "*"sin_lat_rad"+" + cos_lat_rad + "*"cos_lat_rad"*(" + sin_lon_rad + "*"sin_lon_rad"+" + cos_lon_rad + "*"cos_lon_rad")) AS "distance_acos" FROM parish WHERE ("+sin_lat_rad+" * "sin_lat_rad" +"+ cos_lat_rad +"* "cos_lat_rad" * (+"+sin_lon_rad +"* "sin_lon_rad" + "+cos_lon_rad +"* "cos_lon_rad")) >"+dis+ " ORDER BY "distance_acos" DESC ", null);
    return cursor;

}

2. 将距离改为:

 if(c.moveToFirst())
        do {
            double distance_acos= c.getDouble(c.getColumnIndex("distance_acos"));
                     String Distance=String.valueOf(Math.acos(distance_acos) * 6380); 
        }while (c.moveToNext());

窗口:

Install minGw充分选择。 更改环境变量:系统变化途径,包括

c:mingwin

测试功能指挥:

g++ --version

复制文档:延伸功能,c, sqlite3.h, sqlite3ext.h, qlite3 ProgramDirectory。 编写和汇编:

gcc -shared -I "path" -o libsqlitefunctions.so extension-functions.c

(path = qlite3ext.h;即C:sqlite3)

如果该方案得以建立,允许装备延期,则以下工作将:

   sqlite> SELECT load_extension( ./libsqlitefunctions.so );

   sqlite> select cos(radians(45));

   0.707106781186548

SQLite 远程办公 implementation: From: https://www.movable-type.co.uk/scripts/latlong.html https://en.wikipedia.org/wiki/甲型六氯环己烷_formula

远程办公

This uses the ‘haversine’ formula to calculate the great-circle distance between two points – that is, the shortest distance over the earth’s surface – giving an ‘as-the-crow-flies’ distance between the points (ignoring any hills they fly over, of course!).

甲型六氯环己烷

办法:

a = sin²(Δφ/2) + cos φ1 * cos φ2 * sin²(Δλ/2)

c = 2 * atan2( √a, √(1−a) )
c = 2 * 
d = R * c

φ为纬度,λ为长度,R为地球rad(mean radius = 6,371km);

请注意,需要从摩擦中去除三边功能!

Java:

const R = 6378136.6 ; // meters equatorial radius
const φ1 = lat1 * Math.PI/180; // φ, λ in radians
const φ2 = lat2 * Math.PI/180;
const Δφ = (lat2-lat1) * Math.PI/180;
const Δλ = (lon2-lon1) * Math.PI/180;

const a = Math.sin(Δφ/2) * Math.sin(Δφ/2) +
          Math.cos(φ1) * Math.cos(φ2) *
          Math.sin(Δλ/2) * Math.sin(Δλ/2);
const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));

const c = 2 * Math.asen(MIN (1, Math.sqrt(a))); //sqlite implementation

const d = R * c; // in metres

远程办公 = 2 * R * ASIN( MIN (1, SQRT( SIN( (RADIANS(lat1)-RADIANS(lat2))/2 )^2 + COS( RADIANS(lat1) )*COS( RADIANS(lat2) )*SIN( (RADIANS(long1)-RADIANS(long2))/2 )^2 )))

地球物理特性https://en.wikipedia.org/wiki/ Earth_ellipsvil:Ecuatorial radius: 6378.1366 Kms。 平均rad:6367 Kms

Constant = 2 * 6378136.6 = 12756273.2

ROUND (
      12756273.2 * ASIN(
                        MIN (1 , 
                                SQRT(
                                    POWER( SIN(RADIANS(PAR.Lat1 - PAR.Lat2)/2) , 2) + 
                                    COS(RADIANS(PAR.Lat1)) * COS(RADIANS(PAR.Lat2)) * POWER ( SIN(RADIANS(PAR.Long1 - PAR.Long2)/2) , 2)
                                      )
                            )
                        )
         , 0) AS 远程办公