133

4.2.6.1.1  Determination  of  primary  state  variables
To  increase  comprehensibility,  the  input  information  of  the  processes  shown  in  DFD  5.1.1  is  not  represented. ­
  The  processes  assembled  here  exhibit  a  uniform  structure  in  this  respect.  Basically,  these
receive  values  from  various  sensors,  process  this  using  plausibility  criteria  and  additional  information
(e.g.  sensor  locations),  and  supply  a  “system  state  variable”.  In  many  cases,  primary  state  variables  are
moreover  dependent  on  further  variables  -  as  a  function  of  the  sensor  used  -  (e.g.  speed  error  or  width
correction  for  the  heading  when  using  a  gyro  compass).  These  additional  input  variables  are  likewise
not  represented  in  DFD  5.1.1.  It  should  be  noticed  that  the  sensor  location  represented  in  the  data  flow
diagrams  relates  to  all  sensors  used  in  each  case.  For  each  sensor,  therefore,  the  particular  sensor
location  must  be  transmitted.
Within  the  framework  of  the  task  “State  identification”,  only  those  variables  are  considered  which  describe ­
  the  state  of  the  system  “ship”.  Other  values  determined  by  means  of  the  on-board  sensor  technology ­
  which  describe  the  environment  variables  (eg  wind,  air  temperature)  are  assembled  in  Process
5.2  “Observation  of  the  environment”.
All  processes  to  determine  state  variables  possess  a  uniform  structure.  In  the  process  “Compare  data
and  criteria”,  the  plausibility  of  the  state  variables  received  is  checked.  Plausibility  testing  in  this  context
is  the  checking  of  the  validity  (qualitative)  and  comparison  with  other  independent  data  suppliers  (quantitative). ­
  Plausibility  testing  -  from  the  standpoint  of  the  data  supplier  -  thus  has  an  “internal"  aspect
(checking  the  validity  of  the  own  measured  data)  and  an  “external”  aspect  (comparison  of  the  supplied
datum  with  other  data  sources).  To  assess  the  “quality”  of  the  transmitted  state  variable  by  the  “user”,  it
is  necessary  to  transmit  the  information  concerning  plausibility,  usability  and  source  with  the  state  variable. ­

The  data  flow  “Reference  model”  in  DFD  5.1.1.1  (“Determine  own  ship  position”)  contains  the  geodetic
datum  on  which  the  particular  position  determined  is  based  (geodetic  reference  system)  and  the  sensor
location  (local  reference  system).
In  the  case  of  all  state  variables  which  contain  correction  processes,  a  distinction  must  be  made  on
closer  consideration  between  a  “raw  value”  (sensor  value  without  correction)  and  a  “corrected  value”.
For  the  variables  where  according  to  DIN  13312  “raw  values”  are  defined,  these  are  considered  as  data
types  (eg  KrK,  MgK  in  DFD  5.1.1.2).  If  no  such  definition  exists  (eg  for  SOGX  -  see  DFD  5.1.1.3),  no
additional  data  types  are  introduced.