创建从圆心和半径一SqlGeography多边形圆 [英] Create a SqlGeography polygon-circle from a center and radius

问题描述

我想保存在SQL服务器2008年的地理场转了一圈，使用C＃。

在C＃中我有一个纬度，经度和半径，但我无法找到一个方法来计算将代表圆和 SqlGeography 创建从它的多边形。

我曾尝试下面的函数来创建多边形：

 私人列表<协调> getCirclePoints（坐标中心，半径为INT，INT速度）//速1：360绘制双方2平180等... 
 {
 VAR centerLat =（center.Latitude * Math.PI）/ 180.0 ; //弧度
 VAR centerLng =（center.Longitude * Math.PI）/ 180.0; //弧度
 VAR DIST =（浮点）半径/ 6371.0; // D =角距离覆盖在地球表面
变种circlePoints =新的List<协调>（）; 
的for（int x = 0; X< = 360; X + =速度）
 {
 VAR方位角= X * Math.PI / 180.0; //弧度
 VAR纬度= Math.Asin（Math.Sin（centerLat）* Math.Cos（DIST）+ Math.Cos（centerLat）* Math.Sin（DIST）* Math.Cos（方位角））; 
 VAR经度=（（centerLng + Math.Atan2（Math.Sin（方位角）* Math.Sin（DIST）* Math.Cos（centerLat），Math.Cos（DIST） -  Math.Sin（centerLat）* Math.Sin（纬度）））* 180.0）/ Math.PI; 
 circlePoints.Add（新坐标（（纬度* 180.0）/ Math.PI，经度））; 
} 
返回circlePoints; 
} 
  

，然后尝试转换该列表<协调> 来可解析字符串：

 变种s =POLYGON（（+的string.join（ ，points.ConvertAll（p值=> p.Longitude ++ p.Latitude）.ToArray（））+））; 
无功聚= SqlGeography.STPolyFromText（新System.Data.SqlTypes.SqlChars（（的SqlString）S），4326）; 
  

但它总是抱怨多边形必须是在一个半球，在那里我敢肯定，这是这样的。

我在正确的轨道可言吗？是否有任何其他（简单）的方式来做到这一点？

解决方案

OK，发现我自己的答案。关键是要营造一个点

  VAR点= SqlGeography.Point（纬度，经度，4326）; 
  

然后创建围绕该点

<缓冲区pre> VAR聚= point.BufferWithTolerance（radiusInMeter，0.01，真正的）; //0.01是简化多边形只保留了几个侧面


然后，你可以简单地创建一个的SqlCommand 并添加多边形参数：

  VAR参数=新的SqlParameter（ @多边形，多）; 
 param.UdtTypeName =地理; 
 command.Add（参数）; 
  

希望这将帮助别人的未来都重要！

I would like to save a circle in a sql-server 2008 geography field, using c#.

In c# I have a latitude, a longitude and a radius but I just can't find a way to calculate the polygon that would represent the circle and create a SqlGeography from it.

I have tried to following function to create the polygon:

    private List<Coordinate> getCirclePoints(Coordinate center, int radius, int speed)  //speed 1: draws 360 sides, 2 draws 180 etc...
    {
        var centerLat = (center.Latitude * Math.PI) / 180.0;  //rad
        var centerLng = (center.Longitude * Math.PI) / 180.0; //rad
        var dist = (float)radius / 6371.0;             //d = angular distance covered on earth's surface
        var circlePoints = new List<Coordinate>();
        for (int x = 0; x <= 360; x += speed)
        {
            var brng = x * Math.PI / 180.0;         //rad
            var latitude = Math.Asin(Math.Sin(centerLat) * Math.Cos(dist) + Math.Cos(centerLat) * Math.Sin(dist) * Math.Cos(brng));
            var longitude = ((centerLng + Math.Atan2(Math.Sin(brng) * Math.Sin(dist) * Math.Cos(centerLat), Math.Cos(dist) - Math.Sin(centerLat) * Math.Sin(latitude))) * 180.0) / Math.PI;
            circlePoints.Add(new Coordinate((latitude * 180.0) / Math.PI, longitude));
        }
        return circlePoints;
    }

And then try to convert this List<Coordinate> to a parsable string:

        var s = "POLYGON((" + string.Join(",", points.ConvertAll(p => p.Longitude + " " + p.Latitude).ToArray()) + "))";
        var poly = SqlGeography.STPolyFromText(new System.Data.SqlTypes.SqlChars((SqlString)s), 4326);

But it always complains the polygon has to be on a single hemisphere, where I'm sure it is the case.

Am I on the right track at all? Is there any other (simpler) way to do this?

解决方案

OK, found the answer on my own. The trick is to create a point

var point = SqlGeography.Point(latitude, longitude, 4326);

Then create a buffer around the point

var poly = point.BufferWithTolerance(radiusInMeter, 0.01, true); //0.01 is to simplify the polygon to keep only a few sides

Then you could simply create a SqlCommand and add the polygon as parameter:

var param = new SqlParameter(@"Polygon", poly);
param.UdtTypeName = "Geography";
command.Add(param);

Hope that will help someone else in the future!

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