Why to diff bbox at t from future bbox's of prediction length in "get_target" function of file "jaad_data_layer.py"

[siddiqian-at-ceme]

Your this piece of code

            `target[i,:,:] = np.asarray(session[target_start:target_start+predict_length,:] - 
                                       session[target_start-1:target_start,:])`

inside the function get_target of file jaad_data_layer.py

I can understand that you are subtracting the bbox at current time t from the all the future bbox's which fall inside the prediction length window.

But why?

Why can't we just use the future bbox's of prediction window as it is?