pick up point in a pointcloud

how can I pick up a point in pointcloud.
I use own class to draw point cloud :AIS_MyPoints : public AIS_InteractiveObject

but how can I write this part?
void AIS_MyPoints::ComputeSelection(const Handle(SelectMgr_Selection)& aSelection,
const Standard_Integer unMode)
{

}
Thanks

SunHongLei's picture

any one know?