

 General Introduction
 
 It is  assumed that the user has read the QD3D User Guide before
 reading this 3D Reference Manual.
 
 Many of  the terms  and capabilities  from QD2D, such as element
 names, are  applicable to  QD3D.  There  are  a  few  exceptions
 however:
 
 1.     QD3D does not support symbols, dimensions, or ellipses.
 
 2.     QD3D does  not support vector plotting. To plot, the user
        must pass the information to QD2D via a text file.
 
 3.     QD3D supports cylinders, revolved arcs and paths.
 
 4.     In QD3D, a part is equivalent to a sub-drawing in QD2D.
 
 5.     The user  may read a part into the working area as a sub-
        part. If  so the  sub-part is  regarded as one entity and
        may be moved, deleted, changed and unpacked as such.
 
 6.     QD3D supports both QD2D and QD3D text files.
 
 
 Structure of QD3D Data
 
 Points are  the most  basic  graphical  element  in  QD3D.  QD3D
 graphical information  is  stored  basically  as  the  following
 attributes:
 
 - Points with three co-ordinates plus a colour and layer.
 - Lines with two end-points.
 - Curves with definition points.
 - Circles/Arcs with five definition points.
 - Planes with definition points.
 - Cylinders with three definition points, a vector and an angle.
 - Revolved  arcs with  four definition  points, a vector and two
   angles.
 - Paths with definition points and an  orientation vector.
 - All graphics attributes are related back to the points.
 
 Thus, whenever  the status  of a  point is  altered,  all  other
 attributes associated  with the  point are altered. For example,
 if a  point is  moved, then  all the  lines linked  to the point
 would be redrawn to the new position.
 
 QD3D stores  each point's  co-ordinates as  real floating  point
 numbers.  There are virtually no limits to the size of the final
 drawing sheet except for the physical limitations of the plotter
 to which  the system  is  interfaced.  Practical  limits  to  be
 observed are  no points  closer than  .01 nor further apart than
 10,000,000.
 
 
 Controlled Replay of Previous Sessions
 
 QD3D writes  a transcript   of   the  user's  session. Should  a
 system  crash  occur  due  to  power  failure, hardware fault or
 software error,  the user  would be  able to recover most if not
 all of his/her work. (A file containing observed user's mistakes
 (ERRORS.Q3D) is also maintained.)
 
 The replay can be performed at four different speeds.

 In the SLOW mode all previous user actions (menu selection, KEY-
 BOARD entry)  are considered  as break-points and are displayed.
 The replay  is continued  if the  user presses  the  RETURN  key
 following a break point. A secondary benefit of this facility is
 that  training   programs  or   demonstration  sessions  can  be
 established.
 
 In the  NORMAL  mode,  only    previous  KEY-BOARD  entries  are
 considered to  be break-points,  the replay will continue if the
 RETURN key is pressed. If any other key is pressed, the user has
 the option  to terminate  the replay and proceed  as in a normal
 session.
 
 In the  FAST mode,  there are  no break-points  and the user can
 revert the replay to the NORMAL mode by pressing any key.
 
 In AUTO mode, the replay will be continuous, looping back to the
 start when a QUIT command is reached.
 
 To stop  the replay,  type "$".  If the  replay is in AUTO mode,
 this will also cause QD3D to terminate. If not then the user can
 revert back to command mode in QD3D.
 

