autocad2008利用objectarx二次开发，从画出的圆中得到它的圆心坐标和半径，怎样编程实现

void GetCircleInfo()
{
ads_name ent;
ads_point p1;
while(acedEntSel(_T("\n选择圆:"),ent,p1)==RTNORM){
AcDbObjectId id;
if(Acad::eOk != acdbGetObjectId(id,ent)) cont