FIELDWORK NO.
9
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Date: ________________________
Location:____________________
Time/Temp.:
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TITLE:
OBJECTIVE/S:
Group
No.:
Weather:
CLOSE COMPASS TRAVERSE
a) To determine the magnetic bearing of each line of an
open compass traverse.
b) To learn how to adjust close compass traverse.
EQUIPMENTS:
Fig. 9.1 Brunton Pocket
Fig. 9.4 Markers
Compass
Fig.9.2 Steel Tape
Fig. 9.3 Range Poles
PROCEDURES:
a. Establish at least five traverse stations on the field assigned to be
surveyed. Call these stations A, B, C and so forth.
b. Set up and level the instrument at A and release the needle of the
compass so that it will swing freely on its pivot.
c. Sight the last traverse station and read the magnetic bearing. Record
this as the back bearing of the last line in the traverse.
d. Sight station B and read the compass box. Record this as the forward
bearing of line AB.
e. Transfer the instrument to B and sight station A. Read the compass box
and record this as the back bearing of line AB.
f. Turn towards the direction of C, then read and record the forward
bearing of line BC.
g. Transfer to C and sight on B. Read and record the back bearing of line
BC, then sight on D and also read and record the forward bearing of
line CD.
h. Proceed to the next station and repeat the same process until the last
traverse station is occupied and a forward bearing of the last line has
been read and recorded.
i. With the steel tape, measure the length of each line in the traverse
twice and record the mean as the actual length of the line.
j. The interior angle at each station of the traverse can be computed
easily from the observed forward and back bearings taken from the
station regardless of whether or not the needle is affected locally. A
carefully prepared sketch is important since from it the required
calculations will be obvious.
k. The angular error of closure is determined by subtracting the sum of
the computed interior angles of the traverse from 180 (n-2), where n
is the sum of sides in the traverse. Note that the computed value may
be a positive or negative quantity, and the resulting sign should be
considered in all succeeding computations.
l. The correction for each computed interior angle is determined by
dividing the angular error of closure by the number of traverse
stations. This computed value is then added algebraically to each
computed interior angle to determine the corresponding adjusted
interior angle.
m. Go over the observed bearings and determine which line in the
traverse is free from local attraction or which could be arbitrarily
chosen as the best line. The adjustment of traverse lines affected by
local attraction is then made by starting from the unaffected or best
line.
n. The forward and back bearing of all the other lines in the traverse
affected by the local attraction can then be easily computed and
adjusted by again drawing a sketch thus making all calculations
obvious.
o. Tabulate observed and adjusted values accordingly.
ILLUSTRATIONS:
DATA AND TABULATION:
Table 9.1. Adjusted Interior Angle
LINE
LENGTH
OBSERVED BEARING
FORWARD
BACK
STA
COMPUTE
D INT.
ANGLE
CORR
ADJUSTED
INT. ANGLE
AB
BC
CD
DE
EF
FA
Table 9.2. Adjusted Bearing
LINE
LENGTH
ADJUSTED BEARING
FORWARD
BACK
AB
BC
CD
DE
EF
FA
COMPUTATION:
CONCLUSION:
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RECOMMENDATION:
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