diff --git a/src/ApplicationServices/mesh/createBoard.ts b/src/ApplicationServices/mesh/createBoard.ts
index 676670cd6..a678f92ce 100644
--- a/src/ApplicationServices/mesh/createBoard.ts
+++ b/src/ApplicationServices/mesh/createBoard.ts
@@ -1,6 +1,6 @@
 import { ExtrudeGeometry, Matrix4, Mesh, Shape, Vector2 } from 'three';
 import { Shape2 } from '../../DatabaseServices/Shape2';
-import { AsVector3, equaln, equalv2, polar } from '../../Geometry/GeUtils';
+import { angle, AsVector3, equaln, equalv2, polar } from '../../Geometry/GeUtils';
 import { RotateUVs } from '../../Geometry/RotateUV';
 
 export namespace CreateBoardUtil
@@ -10,37 +10,26 @@ export namespace CreateBoardUtil
     {
         _StartAn: number;
         _EndAn: number;
-        _StartPoint: Vector2;
-        _EndPoint: Vector2;
         _Center: Vector2;
         _Radius: number;
         constructor(p1: Vector2, p2: Vector2, bul: number)
         {
-            this._StartPoint = p1.clone();
-            this._EndPoint = p2.clone();
-
-            let vec: Vector2 = p2.clone().sub(p1);
-            let len = vec.length();
-            let an = vec.angle();
-            this._Radius = len / Math.sin(2 * Math.atan(bul)) / 2;
-            let allAngle = Math.atan(bul) * 4;
-            let delDis = bul * len / 2;
-            let toDis = this._Radius - delDis;
-            an += Math.PI * 0.5;
-
-            this._Center = p1.clone().add(p2);
-            this._Center.multiplyScalar(0.5);
-
-            polar(this._Center, an, toDis);
-
-            this._StartAn = p1.clone().sub(this._Center).angle();
-            this._EndAn = p2.clone().sub(this._Center).angle();
-            if (bul < 0)
-            {
-                //一个神奇的特性 它需要这么做
-                this._StartAn -= Math.PI;
-                this._EndAn -= Math.PI;
-            }
+            p1 = p1.clone();
+            p2 = p2.clone();
+
+            //a (* 2 (atan b))
+            let a = Math.atan(bul) * 2;
+            //r (/ (distance p1 p2) 2 (sin a))
+            let r = p1.distanceTo(p2) / 2 / Math.sin(a);
+            //c (polar p1 (+ (- (/ pi 2) a) (angle p1 p2)) r)
+            let c = polar(p1.clone(), Math.PI / 2 - a + angle(p2.clone().sub(p1)), r);
+
+            this._Radius = Math.abs(r);
+
+            this._StartAn = angle(p1.sub(c));
+            this._EndAn = angle(p2.sub(c));
+
+            this._Center = c;
         }
     }