Flex创建带有空间信息的椭圆(Polygon)

运行环境：Flash Builder 4.0+Arcgis API for Flex Version 2.1类库

本来在ArcGIS Flex API中是不能直接画椭圆的polygon的，后来想到调用GP服务画椭圆，但是效率很低下，画一个椭圆要花个好几秒，最直接的办法就是自己创建

 

 1 private function CreateLocalEllpise(centerPoint:MapPoint,prolateAxis:Number,minorAxis:Number,includedAngle:Number):Polygon
 2            {
 3                var cX:Number=centerPoint.x;
 4                var cY:Number=centerPoint.y;
 5                
 6                var paramB:Number=includedAngle*Math.PI/180;
 7                var paramH:Number=0.02;
 8                var paramR:Number=0;
 9                
10                if(prolateAxis>=minorAxis)
11                {
12                    paramR=Math.pow(prolateAxis,2)/minorAxis;
13                }
14                else
15                {
16                    paramR=Math.pow(minorAxis,2)/prolateAxis;
17                }
18                
19                var paramA:Number=Math.acos(1-(paramH/paramR));
20                var startAngle:Number=0;
21                var pointArray:Array=new Array();
22                while(startAngle<(2*Math.PI))
23                {
24                    
25                    var  dx:Number = cX + prolateAxis * Math.cos(startAngle) * Math.cos(paramB) - minorAxis * Math.sin(startAngle) * Math.sin(paramB);
26                    var  dy:Number = cY + prolateAxis * Math.cos(startAngle) * Math.sin(paramB) + minorAxis * Math.sin(startAngle) * Math.cos(paramB);
27                    
28                    var   myPoint:MapPoint=new MapPoint();
29                    myPoint.x=dx;
30                    myPoint.y=dy;
31                    
32                    pointArray.push(myPoint);
33                    
34                    startAngle+=paramA;                   
35                }
36                
37                var myPg:Polygon=new Polygon();
38                 myPg.addRing(pointArray);
39                 
40                 return myPg;
41            
42            }
43 
这个是最初写的代码，将上面画出椭圆，作为query.Geometry，在querytask和query中进行intersect操作时会报错，报错信息如下: fault code:400 Unable to perform query. Please check your parameters.但进行contains操作不会报错。这个其实是个很恶心的错误，在用querytask时如果报错很多都是这个错误，仅从这里是看不出来的，我们从ArcServer的日志下手吧，日志中有这样的错误信息:“Polygon does not close properly”;说明我们的polygon几何类型没有闭合，对上述代码进行改进
 
代码
 1    private function CreateLocalEllpise(centerPoint:MapPoint,prolateAxis:Number,minorAxis:Number,includedAngle:Number):Polygon
 2            {
 3                var cX:Number=centerPoint.x;
 4                var cY:Number=centerPoint.y;
 5                
 6                var paramB:Number=includedAngle*Math.PI/180;
 7                var paramH:Number=0.02;
 8                var paramR:Number=0;
 9                
10                if(prolateAxis>=minorAxis)
11                {
12                    paramR=Math.pow(prolateAxis,2)/minorAxis;
13                }
14                else
15                {
16                    paramR=Math.pow(minorAxis,2)/prolateAxis;
17                }
18                
19                var paramA:Number=Math.acos(1-(paramH/paramR));
20                var startAngle:Number=0;
21                var pointArray:Array=new Array();
22                var starPoint:MapPoint=new MapPoint();
23                while(startAngle<(Math.PI*2))
24                {
25                    
26                    var  dx:Number = cX + prolateAxis * Math.cos(startAngle) * Math.cos(paramB) - minorAxis * Math.sin(startAngle) * Math.sin(paramB);
27                    var  dy:Number = cY + prolateAxis * Math.cos(startAngle) * Math.sin(paramB) + minorAxis * Math.sin(startAngle) * Math.cos(paramB);
28                    
29                    var   myPoint:MapPoint=new MapPoint();
30                    if(startAngle==0)
31                    {
32                        starPoint.x=dx;
33                        starPoint.y=dy;
34                    }
35                    
36                    
37                    myPoint.x=dx;
38                    myPoint.y=dy;
39                    
40                    
41                    pointArray.push(myPoint);
42                    
43                    startAngle+=paramA;                   
44                }
45                pointArray.push(starPoint);
46                 var myPg:Polygon=new Polygon();
47                 myPg.addRing(pointArray);
48 
49                 return myPg;           
50            }
51 
 
 

这样就可以了， var paramH:Number=0.02;
这句话为什么要取0.02?因为这是经验参数吧，一般取值范围在0.01-0.03之间都可以