//从圆弧一些信息得到圆弧上一个特殊的点(计算的是二维图形的情况)Point3d DBOPERATION::GetArcTangencyPoint(Point3d pStartPoint, Point3d pEndPoint,

Point3d pCenterPoint,doubledRadius,doubledStartAngle,doubledSweepAngle)

{

Point3d pResultPoint;

pResultPoint.X=0;

pResultPoint.Y=0;

pResultPoint.Z=0;//因为会得到两个点,哪个点在弧上需要再进行判断doubledRx1=0;doubledRx2=0;doubledRy1=0;doubledRy2=0;constdoublePI=3.1415926535897932;

Point3d pMiddlePoint;

pMiddlePoint.X=(pStartPoint.X+pEndPoint.X)/2;

pMiddlePoint.Y=(pStartPoint.Y+pEndPoint.Y)/2;

pMiddlePoint.Z=0.0;//扫角的角度值doubledArcSweepAngle=180*dSweepAngle/PI;//中点到圆心的距离doubleddy=0;doubleddx=0;if(pMiddlePoint.X-pCenterPoint.X>=0.1e-6)

{

ddx=pMiddlePoint.X-pCenterPoint.X;

}if(pMiddlePoint.Y-pCenterPoint.Y>=0.1e-6)

{

ddx=pMiddlePoint.Y-pCenterPoint.Y;

}doubledDistance=sqrt(ddx*ddx+ddy*ddy);if((fabs(pMiddlePoint.Y-pCenterPoint.Y)<0.1e-6&&fabs(pMiddlePoint.X-pCenterPoint.X)<0.1e-6)&&(fabs(pStartPoint.X-pEndPoint.X)<0.1e-6||fabs(pStartPoint.Y-pEndPoint.Y)<0.1e-6))

{//半圆且斜率=0或者斜率为无穷大的情况if(fabs(pStartPoint.X-pEndPoint.X)<0.1e-6)

{//结果的两个X的值dRx1=pMiddlePoint.X+(dRadius-dDistance);

dRx2=pMiddlePoint.X-(dRadius+dDistance);//对应的两个Y的值dRy1=pMiddlePoint.Y;

dRy2=pMiddlePoint.Y;

}if(fabs(pStartPoint.Y-pEndPoint.Y)<0.1e-6)

{//结果的两个X的值dRx1=pMiddlePoint.X;

dRx2=pMiddlePoint.X;//对应的两个Y的值dRy1=pMiddlePoint.Y+(dRadius-dDistance);

dRy2=pMiddlePoint.Y-(dRadius+dDistance);

}

}elseif(fabs(pMiddlePoint.Y-pCenterPoint.Y)<0.1e-6&&fabs(pMiddlePoint.X-pCenterPoint.X)>=0.1e-6)

{//圆心与端点中心点在水平线上的情况,斜率=0//结果的两个X的值dRx1=pMiddlePoint.X+(dRadius-dDistance);

dRx2=pMiddlePoint.X-(dRadius+dDistance);//对应的两个Y的值dRy1=pMiddlePoint.Y;

dRy2=pMiddlePoint.Y;

}elseif(fabs(pMiddlePoint.X-pCenterPoint.X)<0.1e-6&&fabs(pMiddlePoint.Y-pCenterPoint.Y)>=0.1e-6)

{//圆心与端点中心点在垂直线上的情况,斜率=无穷大//结果的两个X的值dRx1=pMiddlePoint.X;

dRx2=pMiddlePoint.X;//对应的两个Y的值dRy1=pMiddlePoint.Y+(dRadius-dDistance);

dRy2=pMiddlePoint.Y-(dRadius+dDistance);

}else{//圆弧两个端点成线的斜率,已经排除了等于0或者无穷大的可能性doubledTheKSAE=(pEndPoint.Y-pStartPoint.Y)/(pEndPoint.X-pStartPoint.X);//与端点组成的线垂直的线的斜率(0度,180度,360度弧的dk需要特殊处理)doubledK=(1/dTheKSAE)*(-1);if(fabs(fabs(dArcSweepAngle)-360)<0.1e-6)

{

dK=(pMiddlePoint.Y-pCenterPoint.Y)/(pMiddlePoint.X-pCenterPoint.X);

}if(fabs(fabs(dArcSweepAngle)-180)<0.1e-6)

{

dK=(pStartPoint.Y-pCenterPoint.Y)/(pStartPoint.X-pCenterPoint.X);

dK=(1/dK)*(-1);

}if(fabs(fabs(dArcSweepAngle)-0)<0.1e-6)

{

dK=(pMiddlePoint.Y-pCenterPoint.Y)/(pMiddlePoint.X-pCenterPoint.X);

}///这是经过两端点中点并与两端点组成的直线垂直的直线的方程//k为斜率,M(x),M(y)分别为中心点坐标值//y=k * x - k * M(x) + M(y)///求出- k * M(x) + M(y)部分的值doubledDif=(-1)*dK*pMiddlePoint.X+pMiddlePoint.Y;///[x - C(x)]^2 + [y - C(y)]^2 = r^2//代入上面的y,其中- k * M(x) + M(y)以dDif代替//[x - C(x)]^2 + [kx + dDif - C(y)]^2 = r^2//下面以dBetween代替+ dDif - C(y)/doubledBetween=dDif-pCenterPoint.Y;///x^2 + 2*C(x)*x + [C(x)]^2//+//(kx)^2 + 2*k*dBetween*x + (dBetween)^2//= r^2///再求中间值doubledNx=(2*dK*dBetween-2*pCenterPoint.X)/(1+dK*dK);doubledLa=(dRadius*dRadius-pCenterPoint.X*pCenterPoint.X-dBetween*dBetween)/(1+dK*dK);doubledAd=dLa+dNx*dNx/4;//结果的两个X的值dRx1=sqrt(dAd)-dNx/2;

dRx2=(-1)*sqrt(dAd)-dNx/2;//对应的两个Y的值dRy1=dK*dRx1-dK*pMiddlePoint.X+pMiddlePoint.Y;

dRy2=dK*dRx2-dK*pMiddlePoint.X+pMiddlePoint.Y;

}//对得到的两个点进行判断,找到在弧上的那个pResultPoint.X=dRx1;

pResultPoint.Y=dRy1;if(fabs(fabs(dArcSweepAngle)-180.0)<0.1e-4)

{//半圆情况处理doublep1x,p1y,p2x,p2y,qx,qy,dx1,dy1,dx2,dy2,det;

p2x=pStartPoint.X;

p2y=pStartPoint.Y;

p1x=pCenterPoint.X;

p1y=pCenterPoint.Y;

qx=dRx2;

qy=dRy2;

dx1=p2x-p1x;

dy1=p2y-p1y;

dx2=qx-p2x;

dy2=qy-p2y;

det=dx1*dy2-dx2*dy1;

BOOL bBlockWise=TRUE;if(det>0.0)

{//逆时针方向bBlockWise=FALSE;

}if(((!bBlockWise)&&(dArcSweepAngle>0.0))||((bBlockWise)&&(dArcSweepAngle<0.0)))

{

pResultPoint.X=dRx2;

pResultPoint.Y=dRy2;

}

}else{//非半圆的情况doubledd1=sqrt(pow(dRx1-pMiddlePoint.X,2)+pow(dRy1-pMiddlePoint.Y,2));doubledd2=sqrt(pow(dRx2-pMiddlePoint.X,2)+pow(dRy2-pMiddlePoint.Y,2));if(((dd1180.0))||((dd1>dd2)&&(fabs(dArcSweepAngle)<180.0)))

{

pResultPoint.X=dRx2;

pResultPoint.Y=dRy2;

}

}returnpResultPoint;

}

posted on 2010-09-08 10:12 老马驿站 阅读(338) 评论(0)  编辑 收藏 引用 所属分类: c++