 Lines, Introduction

 Lines can  be added, deleted or modified. Lines are always added
 or changed  with respect to the current colour, layer and opaque
 definitions. These  definitions  will  remain  in  effect  until
 changed by the user.

 Lines can  be added  freehand using  the puck, based on existing
 points, using  keyboard  entries,  or  any combination of these.
 In  addition  there  are  several  line options available to add
 lines relative to existing elements.

 Lines can  be made  to show  on  hidden  surface  renderings  by
 nominating them as "opaque".

 Lines may be located by snapping to one of their end points with
 the left  puck button or by using the central button anywhere on
 the line.


 "LINE OPT"

 When this command is selected, a display of LINE options appears
 in tertiary  menu. The  user is  prompted  to  choose  one.  The
 options are:

      Option         Nature of Option

      ANGLE          A reference  line is  located and  an  angle
                     specified.  All   lines  added  within  this
                     command from  this point on will snap to the
                                                      ____       
                     nearest  multiple  of  the  specified  angle
                     relative to the reference line. This command
                     is very useful for adding parallel lines.


      SECTORS        Three points are located to define an angle.
                     The angle  is defined point 1, through point
                     2 to  point 3.  The angle  defined by  these
                     three  points   is  calculated  and  a  user
                     specified number  of  lines  is  added  from
                     point 2, so that the angle between each line
                     added is equal.

                     The length of these lines will vary from the
                     length of  point 2  to point 1 to the length
                     of point  2 to point 3. All lines in between
                     decrease or  increase in length accordingly.
                     The user  must be careful in which direction
                     point 1,  point 2,  point 3 are selected, as
                     all new lines are added in an anti-clockwise
                     sense.


      TAN CIR2       Two circles  are located,  each one  located
                     near the  desired tangent  point. A  line is
                     then added which is tangent to both circles,
                     and extends  from one  tangent point  to the
                     other.


      TAN CIR1       A circle is located near the desired tangent
                     location and then a point is located. A line
                     is drawn  from that point to the circle, and
                     that line is a tangent to the circle.

   

      TAN ANG        A circle is located an angle specified, then
                     a reference  line located.  A line  is added
                     tangent to  the  circle  and  at  the  angle
                     specified relative to the reference line.

      In almost all cases, (unless the line is a tangent), a line cuts
      a circle  in two  places. When you are asked to locate a circle,
      the screen  position used  to locate  the circle  determines the
      tangent   intersection   point   used.   The   nearest   tangent
      intersection point to that location is the one used.

      PLA PLA         A single  plane which  will intersect others
                      is  located,  then  a  group  of  planes  is
                      selected.   Lines will  be added  where  the
                      first plane  intersects each  plane  in  the
                      group.   The method used to locate the group
                      is selected via a tertiary menu which allows
                      either  location   of  individual   elements
                      (planes), an enclosing block or an enclosing
                      polygonal  fence.    Individual  planes  are
                      selected by  the left  button  on  a  corner
                      point or  the central  button on the average
                      of the corners.


 "LINE ADD"

 This command  is used  to add  lines using the currently defined
 pen and  layers. Lines   may   be  added freehand,  by  snapping
 to   existing   points,   or by  keyboard entry.  When lines are
 added freehand,  the snap   mode   can   be  used  to  assist in
 adding the  lines accurately.  The keyboard entries described in
 HELP POINT, may also be used  when  adding lines.

 When the two points defining the line have been added, a line is
 drawn to  join the  two points.  If the next line continues from
 the end  point of the last line, the user can continue simply by
 locating another  co-ordinate. Pressing  the termination  button
 once, allows  the user  to begin a new line at another location.
 Pressing the  termination button  twice in succession terminates
 the LINE ADD command.

 Procedure
 .   Locate the position on the screen for the start of line.
 .   Locate the position on the screen for the end of the line.


 "LINE DEL"

 This command  is used  to delete  lines from  the  current  sub-
 drawing. When  this command is selected QikDraw prompts the user
 to locate line(s) to be deleted.


 "LINE CHANG"

 When this  command is  selected a  tertiary menu  appears  which
 allows the current values of colour, layer and opaque setting to
 be changed.   This  tertiary menu  also allows the colour and/or
 layer and/or  opacity of  a group  of lines  to be changed.  The
 method of  locating the group is at the top of the tertiary menu
 ( see POINT CHANG).


 "LINE BREAK"

 This command  is used  to break  a single  line up  into shorter
 lines. The  user locates the line and that line is broken into a
 separate portion  every time  a point  is encountered  along its
 length. Thus to use this command, the user must first add points
 to the  line at  the intervals  required. These points determine
 the location of each break.

 Once the  line has  been broken  the command  reports  how  many
 segments  the  line  was  broken into.


 "LINE EXTEN"

 This   command   is used to extend (or shrink)  lines  to  other
 existing   elements.    Lines can be extended to another line, a
 plane, a  circle, by  a prescribed distance or to a given point.
 In   all cases  the line to be modified must be located near the
 end of the line which is to be extended.

 In each case, the line to be extended is located first, then the
 entity of appropriate type.

 When this  command is  selected, a display of options appears in
 tertiary menu. The user is prompted to choose one. These options
 are:

      Option         Nature of Option

      PLANE          A  line  and  plane  are  selected  and  the
                     reference line is extended to the line/plane
                     intersection. If  the two  entities  already
                     intersect, then  the line  is shrunk so that
                     it stops at this intersection point.


      CIRCLE         A line  and a  circle are selected. The line
                     is extended or shrunk so that it ends at the
                     line/circle intersection.  Because, in  most
                     cases, there  are two  possible intersection
                     points, the  line is  extended to  the point
                     nearest the  screen location  used to select
                     the circle.


      LINE           A line  is extended  so that  it ends at the
                     intersection   of    itself   with   another
                     reference line.


      POINT          A point  and a  reference line are selected.
                     QikDraw constructs an imaginary line through
                     the point, normal to the reference line. The
                     reference line is extended or shrunk so that
                     it ends  on the  intersection of  itself and
                     the imaginary normal.


      DISTANCE       A  line  can  be  extended  by  a  specified
                     distance. For example, a distance of 20 will
                     cause the  line to  be stretched by 10 units
                     and a distance of -20, shrunk by 20 units.


