Civil Engineering Reference
In-Depth Information
Fig. 4.11
Magnetic dip
obtain the bearing of one boundary or traverse line. A theodolite or total station
will then be used to measure precise angles from this line to all other lines in the
survey. Using this method, the boundary measurements will be precise. Only the
orientation of the parcel will be limited to the accuracy of the compass and the
stability of the magnetic field. This latter deficiency can mitigated by setting per-
manent boundary markers on the ground to orient the parcel.
During the nineteenth century, and earlier, surveyors were limited to using a
compass to obtain a magnetic bearing for the survey, or making astronomical obser-
vations to determine true north. Making astronomical observations is time con-
suming and it is sometimes cloudy. As a result, determining true north was rarely
used for small surveys. For surveys that did not require precise measurements,
boundaries were measured using only a magnetic compass and a chain. Because the
method is imprecise, this technique is rarely used today for boundary determina-
tion. However, modern surveyors performing retracement surveys of these ancient
surveys must take these factors into consideration when locating boundaries so they
must understand the issues associated with magnetic measurements.
