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Survey procdures for a closed traverse

A closed traverse is used to measure an enclosed polygonal area consisting of straight sides. The result of a traverse is a vector model of the polygon, with angles and lengths as well as real-world coordinates of the vertices of the polygon, and knowledge about the error of measurement.

jump to Field Procedure | Office Procedure

Field procedure

1. Form teams of three. At least one person on each team should have taken ESRM 250 or have experience using ArcGIS.
2. Make sure each team has a compass, clinometer, measuring tape, and field notebook.
3. Traverse the stations as indicated in the assignment instructions.
4. Take careful field notes indicating:
   1. Date, time, and weather conditions (including temperature if you can get it)
   2. City and state (for magnetic declination)
   3. Crew members present
   4. Make and model of measurement equipment
      
      
      
      
   5. A rough sketch of the area including station locations and IDs
   6. Station numbers
   7. Foreshot and backshot (planimetric) angles using the compass (as azimuth in degrees)
      Note: the example below uses quadrant bearings (e.g., S 38° E) but it will be simpler to record the numerical angle from 0 to 360°.
   8. Slope distance from station to station using the tape measure
      
   9. Slope (elevation) angles using the clinometer (in degrees)
      Note: the example below uses slope in %, but it will be more efficient in post-processing to record in degrees.
      
      Do NOT attempt to collect difference in elevation (it cannot be done using the equipment we have)
      
      
      
      

   The suggested method will be (assuming a start at station 1, measuring to station 2):

   1. Two people stay at the first station (one to take notes and the other to make measurements).
   2. The third person will take the numerically small end of the measuring tape to the second station.
   3. Person 1 at station 1 will measure, and person 2 will record:
      1. foreshot angle (as azimuth, i.e., 1° to 360°)
      2. elevation angle (as degrees; note + or –)
      3. distance to station 2 (note: hold the measuring tape at waist height at both locations, and
   4. The crew will move to station 2 with the compass and notebook while person 1 stays at station 1.
      1. Person 2 will measure the backshot angle (from station 2 to station 1).
   5. Repeat the process until all stations have been visited (it will be necessary to return the the first station at the end of the traverse to record all necessary data).
      

   A note about error in the foreshot and backshot angles: The "perfect" sum of interior angles for this traverse of 4 stations should be 360°. The maximum allowable error is k * sqrt(4), where k is the smallest division on the compass (2°), therefore the maximum allowable error is 4°. If the sum of your interior angles differs from 360° by more than 4°, you can either remeasure your angles (best practice) or distribute the error by post-processing calculation (worse practice).

Office procedure

1. Correct for declination by adding (or subtracting) the correction for each azimuth.
   Magnetic north is east of true north in Seattle; should you add or subtract the correction factor?
2. Obtain interior angles by calculation from foreshots and backshots.
3. Calculate interior angle error and adjust the interior angles, then recalculate the azimuth of each line based on the correction of the angles.
4. Correct the measured distances for slope
5. Calculate the latitudes and departures.
6. Calculate corrected coordinates for each point.
7. Establish (calculate) your error of closure (EOC) and precision.
8. Calculate the area of your traverse (use the coordinate method for this course).
9. Create a rough hand-drawn graph of the area indicating the interior angles and distances.
10. Complete the report (the assignment).