
 Circles, Introduction
 
 The CIRCL  commands are  used to  manipulate circles  and  arcs.
 Circles/arcs can  be added  in various  ways relative to various
 entities.
 
 In a  circle is planar and the points defining the start and end
 of the arcs must lie on this plane.
 
 Ellipses are not currently supported in QD3D.
 
 
 "CIRCL ADD"
 
 When CIRCL  ADD is  selected, the  user is prompted to select an
 add option from tertiary menu. These options include:
 
      Option      Implementation
 
      CEN+RAD     By a  centre point  plus  a  specified  radius.
                  Specify the  radius and place the centre point.
                  The circle  is constructed so it is in the same
                  plane as that defined by the current view.
 
      CEN+PNT     By  a   centre  point   plus  a  point  on  the
                  circumference. The centre point is located then
                  a   circumference    point.   The   circle   is
                  constructed so  it is in the same plane as that
                  defined by the current view.
 
      3 PT END    By three  points on the circumference. The user
                  locates each of the three points in turn.
 
      3 PTS      A centre  point, a  circumference  point  and  a
                  point in  the desired plane in which the circle
                  is drawn.  The user locates the centre point, a
                  circumference  point  and  the  plane  defining
                  point.
 
      RAD+PLA     A plane  parallel to the plane the circle is to
                  lie in  is located.  The circle  centre is then
                  located and  a radius  specified. The reference
                  plane is  located, the radius specified and the
                  circle centre located.
 
      TAN+CEN     By a centre point plus a tangent line. The line
                  is located then the circle centre.
 
      2TAN+RAD    By two  tangent lines  plus a specified radius.
                  The circle radius is specified, the two tangent
                  line located  and an  approximate position  for
                  the circle centre.
 
      3 TANGT     By three tangent lines. The three tangent lines
                  are located and an approximate position for the
                  circle centre.
 
      NOR+CEN     By a line perpendicular to the plane the circle
                  is to  lie in,  the circle  centre and a circle
                  radius.  First,  the  normal  is  located,  the
                  radius specified and the circle centre located.
 
 The user  is prompted  to locate  the appropriate  entity and/or
 specify the radius.

   
 "CIRCL DEL"
   
 Circle/arcs are  deleted in  the same way as lines. Refer to 3.3
 LINE DEL for details. They are located the same way as lines; by
 locating the  PUCK anywhere  on their circumference and pressing
 the selection button.
 
 
 "CIRCL TRANS"
 
 This command  is used  to transform  a circle into an arc, or to
 change the  start and  end points  of an  arc.  Two  points  are
 located on  the circle  circumference and any part of the circle
 that does  not lie between those two points in an anti-clockwise
 sense is  erased. To  transform an arc into a circle, locate the
 same point twice.
 
 Procedure
 .   Locate the circle to transform.
 .   Locate two points in turn to define the arc.
 
 
 "CIRCL CHANG"
 
 Circle/arc attributes  can be  changed by the same method as for
 points lines et cetera (see 2.6 POINT CHANG).
 
 
 "CIRCL BREK"
 
 This  command  allows  the  user  to  break  a  circle/arc  into
 segments. The user is prompted to locate the circle/arc and that
 entity is broken into as many arc segments as possible depending
 on how  many points exist on it's circumference. (ie. there will
 be one  less  segment  than  there  are  points  on  the  entity
 circumference).
 
 
 "CIRCL ARC"
 
 This command allows the user to add an arc to the sub-drawing by
 locating  the   centre  point   and  two   points  on   the  arc
 circumference. The  arc is  drawn to join these two points in an
 anti-clockwise manner.
 
 Procedure
 .   Locate the centre point.
 .   Locate in turn the two circumference points.

