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TYING  IN  A  POINT
TRANSIT-TAPE  SURVEY

Engineering Aid 3 - Beginning Structural engineering guide book
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Figure 13-23.-Range ties. Figure 13-24.-Locating a point by stations. distances from two distance. The method requires extra instrument manipulation  and  should  be  used  only  when  none of the previous methods are satisfactory for use. Actually, range ties establish not only the corner of  a  structure  but  also  the  alignment  of  one  of the sides. In figure 13-23, assume that the building is not visible from either A or B or that either or both of the distances from A to B to a corner of the building cannot be measured easily. With the instrument set up at either A or B and the line AB established, one member of the party moves along AB until he reaches point R, which is the intersection of line 1-2 extended. The instrument is moved and set up on R, and the distance along the line AB to R is measured. An angle measure- ment  to  the  building  is  made  by  using  either  A or  B  as  the  backsight.  The  range  distance,  R-2, is measured as well as the building dimensions. SETTING  ADJACENT  POINTS “To  set  a  point  adjacent  to  a  traverse  line” means  to  establish  the  location  of  a  point  by following  given  tie  data.  This  tie  data  may  be (1) a perpendicular offset distance from a single specified station, (2) angles from two stations, or (3)  an  angle  from  one  station  and  the  distance from  another  station. Setting Points When Given a Perpendicular Offset Distance To  set  a  point  when  given  an  angle  and  its distance from a single station, you simply setup the  instrument  at  the  station,  turn  the  designated angle,  and  chain  the  distance  along  the  line  of sight. For perpendicular offset, the angle is 90°. To set a point when given a distance from each of  two  stations,  you  can  manage  by  using  two tapes  if  each  of  the  distances  is  less  than  a full  tape  length.  To  do  so,  you  set  the  zero  end of the tapes on both stations, run out the tapes, and  match  the  distance  mark  on  each  tape  to correspond  with  the  required  distance  from  the stations. When the tape is drawn taut, the point of  contact  between  the  tapes  will  be  over  the location  of  the  desired  point. If one or both of the distances is greater than a full tape length, you can determine direction of one  of  the  tie  lines  by  correct  triangle  solution. For  example,  in  figure  13-24,  you  want  to  set Point B 120.0 ft from station A and 83.5 ft from station  C.  A  and  C  are  117.0  ft  apart.  You  can determine the size of the angle at A by triangle solution  as  follows: To set point B, you can set up a transit at A, sight on C, turn 41°14´ to the left, and measure off 120.0 ft on that line of sight. As a check, you can measure BC to be sure it measures 83.5 ft. Setting Points When Given Angles from Two Stations To set a point when given the angle from each of  two  traverse  stations,  you  should  ordinarily 13-19







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