[Wien] questions

[ËïÉÙÈð]

Dear user: 
      I met a problem when I plot a charge density plane for HgS, which is  hexagonal  structure and the space groupe is P3121. The structure is shown as follows:
   HgS                                                                            
H   LATTICE,NONEQUIV.ATOMS:  2152_P3121                                        
MODE OF CALC=RELA unit=bohr                                                    
  7.819907  7.819907 18.004614 90.000000 90.000000120.000000                   
ATOM  -1: X=0.71923271 Y=0.00000000 Z=0.33333333
          MULT= 3          ISPLIT= 8
      -1: X=0.00000000 Y=0.71923271 Z=0.66666666
      -1: X=0.28076729 Y=0.28076729 Z=0.00000000
Hg1        NPT=  781  R0=0.00000500 RMT=    2.0000   Z: 80.0                   
LOCAL ROT MATRIX:    0.0000000-0.5000000 0.8660254
                     0.0000000-0.8660254-0.5000000
                     1.0000000 0.0000000 0.0000000
ATOM  -2: X=0.49603658 Y=0.00000000 Z=0.83333333
          MULT= 3          ISPLIT= 8
      -2: X=0.00000000 Y=0.49603658 Z=0.16666666
      -2: X=0.50396342 Y=0.50396342 Z=0.50000000
S 1        NPT=  781  R0=0.00010000 RMT=    1.9000   Z: 16.0 
 
I want to set a plane including the centers of the Hg(0.71923271 0.00000000 0.33333333), and S(0.49603658 0.00000000 0.83333333), but I do not know how to  set the coordinations of the origin, the x-end and the y-end, respectively, in the case.in5c file. who can help me?
                                                                       best regard
                                                                                         S. R. Sun