PART I - OFFICE WORK
2-24. General. Surveying procedures also consist of converting field measurements to a more usable
form. Usually, the conversions or computations are required immediately to continue the fieldwork, but
sometimes they must be held until a series of field measurements are completed. This procedure is
known as office work, even though some of the operations may be performed in the field during lapses
between measurements. Some office work requires the use of special equipment (calculators,
computers, or drafting equipment) or extensive references and working areas. During survey operations,
many field measurements require some form of mathematical computation
2-25. Computing. Office computing converts distances, angles, GPS measurements, and rod readings
into a more usable form or adjusts a position of some point or mark from which other measurements can
be made. This process involves the computation of--
a. Distances. The desired result is the horizontal distance between two points. In an electronic
distance measurement (EDM), the distance is usually on a slope and has to be corrected to account for
the temperature and barometric pressure and then reduced to the correct horizontal distance.
b. Azimuths and Bearings. In many operations, the observed angles are converted into directions of
a line from north (azimuths) or north-south (bearings).
c. Relative Positions. The distance and direction of a line between two points determines the
position of one point relative to the other point. If the direction is given as an azimuth bearing, a
trigonometric formula, using the sine or cosine of the angle, multiplied by the distance, will result in a
coordinate difference between the two points.
d. Adjusting. Some survey techniques are not complete until one or more of the following
adjustments are performed. Adjusting is the determination and application of corrections to data.
Adjusting provides a means of dealing with the random errors in a survey network. Adjustment causes
the data to be consistent within itself and to a given set of references. Small errors that are not apparent
during individual measurements can accumulate to a sizable amount. For example, in a linear
adjustment, assume that 100 measurements were made to the nearest unit and required determining
which unit monument was closer to the actual measurement. Adjusting the results requires reducing
each measurement by the product that results from dividing the error by the number of measurements.
Since the measurements were only read to the nearest unit, a single adjustment would not be measurable
at any point, and the adjusted result would be correct. Some of the more precise surveys require least-
square adjustments.
e. Global Positioning System Networks and Least-Square Adjustments. A least-square adjustment
is the basis for correcting GPS (and traverse) networks that use automation to compute solutions in
geometry and produce geodetic accuracy. A
EN0593
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