
 Points, Introduction
 
 Of the  drawing elements  provided by  QD3D, POINTS are the most
 basic and  are used  by  QD3D  to  construct  and  define  other
 entities. Points:
 
       - define the start and end of a line.
       - control the shape of a curve.
       - define the nature of a circle/arc.
       - determine the shape of a plane.
       - determine the shape of a cylinder.
       - may define the location of sub-parts.
       - define the channel of a path.
 
 Points may  be added,   moved and deleted.  Points may be  added
 freehand   by  using the puck.  When snap mode is set  (see 14.3
 SET MODE SNAP for details),   freehand  manipulations   can   be
 made   to   snap  to  the   currently  defined   reference  grid
 points. SNAP  mode is ignored  by  QD3D   when  points are added
 by explicit co-ordinate values using the keyboard, or when using
 the alternate button to snap to (existing) points.
     alternate                                     
 
 When a point is moved or deleted, any other elements (eg. lines,
 curves etc.)  associated with  or defined  by that point will be
 modified to reflect the change.
 
 Whenever a  point is required, the user may either use the puck,
 or type   in   the   co-ordinate  of  the  point  to add.  There
 are several  different keyboard  entries which  can be  used. In
 each case,  a  1  to  3 letter  prefix  is  optionally added  to
 the three co-ordinates to identify the type of  keyboard  entry.
 The  following  table lists the valid keyboard entries.
 
 A        Absolute Cartesian
 R        Relative Cartesian
 CA       Cylindrical Absolute
 CR       Cylindrical Relative
 VA       View Absolute
 VR       View Relative
 VCA      View Cylindrical Absolute
 VCR      View Cylindrical Relative
 CPA      Construction Plane Absolute
 CPR      Construction Plane Relative
 ref      Used to locate a reference point.
 
 The relative  commands are  relative to the last point  located,
 or   added.    The ref command is used to add points relative to
 any existing  point. To  use  the  ref  command,  key  in  "ref"
 followed   by   return.   Then  snap  to  the required reference
 point.   If a  relative keyboard entry is then used, it will  be
 relative to the located point.


 "POINT OPT"
 
 A tertiary  menu of point options is displayed on the screen and
 the user is prompted to select the appropriate option from those
 offered. Those options include:
 
    Option           Nature of Option

    SEGMENTS         A user  specified number of points are added
                     with equal  spacing  between  two  reference
                     points. The  user specifies  how many points
                     to  add,  then  locates  the  two  reference
                     points  the  new  points  are  to  be  added
                     between.


    LIN-LIN          A point  is added at the intersection of two
                     lines. The user must locate the two lines in
                     turn.
 
    LIN-PLA          A point  is added  at the  intersection of a
                     line and  a plane (if the two intersect). If
                     both entities lie in the   same   coordinate
                     axes plane,  then they are not considered to
                     intersect.  The   user   must   locate   the
                     reference line, then the plane.
 
                     A plane is located in one of two ways:
 
                     1. Snap to  any of the plane defining points
                        with the alternate button.
                                 alternate        
                     2. Locate the  plane defining  diamond  (see
                        6.1 PLANE INTRODUCTION for details).
 
    CIR-LIN          A point  is added  at the  intersection of a
                     circle and  a  line.  First  the  circle  is
                     located, then  the line. A point is added on
                     the  circle   circumference  at  every  line
                     intersection point;  there may  be none, one
                     or two.
 
    ARC-SEG          A user  specified number of points are added
                     to a circle/arc at even intervals around its
                     circumference. The  user also has the option
                     of joining  those points  by lines  (an easy
                     way to create polyhedra).
 
    CIR-PLA          Points are  added at  the intersection  of a
                     circle/arc  and   a  plane.  The  circle  is
                     located first, then the plane.
 
    CIR-CIR          Points are  added at the intersection of two
                     circles/arcs. The  user locates  each of the
                     circles in turn.
 
    LIN-REL          Points are  added  relative  to  a  selected
                     line. These can be prefixed by an A or an R.
                     The points are added relative to the nearest
                     line end  to the  screen  location  used  to
                     locate the line. R10 will add a point on the
                     line at  a distance  of 10  units  from  the
                     current position on the line. A45 will add a
                     point at  a distance  45 from the end of the
                     line. The user  locates the  line, then 
                     enters the appropriate coordinates.
       
    Notice that if two entities do not physically intersect, a point
    is still  added at  the location  where they  would intersect if
    they were  extended. If  they  could  never  intersect,  QikDraw
    informs the user in the prompt/dialogue area.
       
       
 "POINT ADD"
       
 When the  POINT ADD  is selected, the user may add points to the
 screen free-hand  style using the selection button. To terminate
 press the termination button.
 Procedure
     . Add points to the screen as desired.
       
       
 "POINT DEL"
       
 This command  is used  to delete  individual  points.  The  user
 locates the point(s) to delete using the alternate puck button.
       
       
 "POINT MOVE"
       
 When this  command is  selected the  user will locate a point on
 the screen  to be moved and then locate freehand the position to
 move it  too. If the user wishes to move the point to a location
 on the  screen already  occupied by  another point, then use the
 alternate button. This indicates to QD3D that the two points are
 to occupy the same position on the screen.
 
 The point   must  first  be  located using the alternate button,
 and then  the new  co-ordinate entered using either the keyboard
 or the  puck. The new  co-ordinate  can  be  specified  relative
 to the  previous position  by   using   any   of   the  relative
 keyboard   entries, because  the last co-ordinate identified was
 the co-ordinate of the point to be moved.
 Procedure
 . Locate the  point to  be moved. Locate the position to move it
   to.
 . Repeat or terminate as desired.
 
 
 "POINT CHANG"
 Procedure
 
 When this  command is  selected a  tertiary menu  appears  which
 allows the  current values  of colour  and layer  to be changed.
 This tertiary  menu also  allows   the colour  and/or layer of a
 group of points to be changed.  The method of locating the group
 is at  the top  of the  tertiary menu  and the  user can  toggle
 between:
 
             Locate    Locate    Locate
             Element   Block     Fence
 


 (using the  central puck  button).  Locate element means snap to
 points one  by one,  locate block means the user will generate a
 rectangle of enclosure on the screen, and locate fence means the
 user will draw a polygonal fence on the screen.
 Procedure
 
 . Indicate in  the tertiary  menu the  new values  of colour and
   layer.
 . Indicate in  the tertiary menu if the colour and/or layer of a
   group of points are to be changed.
 . Indicate in the tertiary menu the method which will be used to
   locate the points.
 . Use the right-hand button to exit from the tertiary menu.
 . If a  block or  fence method was selected then use the central
   button to place this boundary.  If locate element was selected
   then use  the left  button to snap onto each point, then press
   the right-hand button to finish.

