Field measurements in traversing, closed/open traverse

Field measurements in theodolite traversing

1. Horizontal angles at each station: included angles, deflection angles or direct (azimuth) angles, observed on both faces and repeated or in sets to reduce instrumental errors.
2. Lengths of the traverse lines: measured with a steel tape (twice, forward and back, with temperature, tension, slope and sag corrections) or with an EDM/total station.
3. Bearing of the starting line: magnetic bearing by a compass or true bearing by astronomical or GPS observation; in a link traverse, the bearings of the reference lines at both ends.
4. Vertical angles or levels of the stations, where the heights are required or the lengths are inclined (for slope reduction).
5. Details and offsets from the traverse lines (building corners, roads, streams), with a sketch and the station numbers.
6. Station description and referencing (ties to permanent objects), the height of the instrument and signals, and all booking in the field book.

Closed and open traverses

• Closed traverse: a traverse that ends where it began (a closed loop) or that starts and ends on stations of known position (a closed link/connecting traverse). It gives a mathematical check on the field work.
• Open traverse: a traverse that starts at a known station and ends at a point of unknown position, so there is no closing check. It is used for roads, canals, pipelines and similar route surveys, and the angles and lengths must be checked by repeat measurement.

 Closed loop       Closed link        Open traverse
   B----C        K1--1--2--3--K2     A---B
  /      \      (known)  (known)         \
 A        D                               C---D
  \      /                                    \
   F----E                                       E (end,
 (returns to A)   (ends on known K2)            unknown)