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Identifying Points
METHODS  OF  DIRECT  LINEAR measurements

Engineering Aid 3 - Beginning Structural engineering guide book
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recorded in the field book as they are established in  the  field.  The  record  may  be  done  either  by sketch,  by  work  description,  or  by  the  combina- tion  of  the  sketch  and  notes.  The  control  point must  be  referenced  to  some  permanent  type  of object  in  its  vicinity;  if  no  such  objects  exist, REFERENCE HUBS are driven at points where they are unlikely to be disturbed. These ties are important   in   recovering   control   points   that have  been  covered  or  otherwise  hidden  or  in reestablishing them accurately if they have been removed. The  reference  location  of  a  particular  point is recorded on the remarks page of the field book by sketches like those shown in figures 12-8 and 12-9.  For  a  permanent  control  point,  such  as  a triangulation  point,  monument,  or  bench  mark, a  complete  “Station  Description”  is  individually prepared for each station. The field offices of the National  Oceanic  and  Atmospheric  Administra- tion  or  the  National  Geological  Survey  have  these station descriptions on separate cards. This is done so  they  can  easily  run  a  copy  for  anyone requesting  a  description  of  a  particular  station. They  also  maintain  a  vicinity  map  on  which  these Figure 12-8.-Natural objects or man-made structures used as  reference  points. Figure 12-9.-Accurate methods for tying points. points are plotted, and these station descriptions are used in conjunction with this map. The Navy’s public  works  offices  also  maintain  descriptions of stations within their naval reservation and its vicinity  for  immediate  reference. The  methods  of  referencing  points  shown  in figure  12-8  are  ideal  for  recovering  points  that have  been  covered  or  otherwise  hidden,  and  those shown  in  figure  12-9  are  for  reestablishment  of these  points  accurately.  The  methods  shown  in figure  12-9  are  generally  used  in  construction surveys. As  you  gain  more  experience,  you  may  be assigned the task of writing a station description. In doing this, be sure to describe the location in detail, and make a sketch showing the location, ties, and magnetic or true meridian. Make your description concise and clear; and be sure to test its  effectiveness  by  letting  another  EA  (preferably not a member of the survey party that established the  point)  interpret  your  description.  From  the feedback of the interpretation, you can determine the  accuracy  of  your  written  description.  Your description,  for  example,  should  be  written  as follows (refer to figure 12-8): “Point A—plugged G.I.  pipe  65.21  ft  SE  of  NE  corner  of  PWC Admin.  Bldg.  (Bldg.  208)  and  81.42  ft  from  the SE  corner  of  same  building.  It  is  18.18  ft  W  of the center of a circular manhole cover located in Saratoga   Street.” Protecting Markers Markers are to be protected against physical disturbance by the erection of a temporary fence (or  barricade)  around  them.  Sometimes  guard stakes  embellished  with  colored  flaggings  are 12-9







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