How to get the header frame id

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Hello,

I want to make a transformation from my kinect to the base_link. My tf tree is build like this: base_link -> chassis -> Kinect -> front_camera.

I would be best if I can get the transformation matrix which directly transforms the data from front_camera to base_link. Because there will be other sensors in the future I want to make it as dynamic as possible. I had something like this in mind (it's like climbing the tree "backwards", from front_camera to Kinect, from Kinect to chassis, and finally from chassis to base_link):

//the first transformation frames     
#ifndef SOURCE_FRAME
#define SOURCE_FRAME "front_camera"
#endif
#ifndef TARGET_FRAME
#define TARGET_FRAME "Kinect"
#endif

geometry_msgs::TransformStamped ts1;
geometry_msgs::Vector3 rotation;
rotation.x = 0;
rotation.y = 0;
rotation.z = 0;
geometry_msgs::Vector3 translation;
translation.x = 0;
translation.y = 0;
translation.z = 0;

 do{
  ts1 = tBuffer.lookupTransform(TARGET_FRAME, ros::Time(0), SOURCE_FRAME, ros:Time(0), "base_link" ros::Duration(5.0));
   rotation += ts1.transform.rotation;

   translation += ts1.transform.translation;

   ts1.header.frame_id = ts1.child_frame_id;
   ts1.child_frame_id = **????????**

   }while(ts1.header.frame_id != "base_link");

I know this is probably not perfect c++ or code in general, but I hope you get what I want to do. I think I will get the syntax and everything right, but I don't know where to look for a function/way to get the child frame id, when I only have the header frame id?

(If you have a different/easier approach for me, I'd be also grateful for advice)

Thanks for your help!