reading filter values from dtp in routine of transformation

Hello,

I try to read a date from the filter of a dtp and propagate this value during the transformation in a routine. this is my code

 DATA:
*Date parameter from DTP
       i_calday    type /BI0/OICALDAY,
       i_date(16) type n.

    data: t_filter_values type RSBK_TH_RANGE,
          l_filter_values like line of t_filter_values.

    t_filter_values = p_r_request->GET_TH_RANGE( ).

* get DTP
    LOOP AT t_filter_values into l_filter_values.
      move l_filter_values-high to i_date.
      EXIT.
    ENDLOOP.

    I_calday = i_date+8(8).
    RESULT = I_CALDAY.

but when dubbing my code t_filter_values is always empty and I do not see the selections from the dtp. please do you have an idea what is wrong?

thanks