surveying is divided into two major categories: plane and geodetic surveying.
PLANE SURVEYING is a process of
surveying in which the portion of the earth being surveyed is considered a plane.
The term is used to designate survey work in which the distances or areas
involved are small enough that the curvature of the earth can be disregarded
without significant error. In general, the term of limited extent. For small
areas, precise results may be obtained with plane surveying methods, but the
accuracy and precision of such results will decrease as the area surveyed
increases in size. To make computations in plane surveying, you will use
formulas of plane trigonometry, algebra, and analytical geometry.
A great number of surveys are of the
plane surveying type. Surveys for the location and construction of highways and
roads, canals, landing fields, and railroads are classified under plane
surveying. When it is realized that an arc of 10 mi is only 0.04 greater that
its subtended chord; that a plane surface tangent to the spherical arc has
departed only about 8 in. at 1 mi from the point of tangency; and that the sum
of the angles of a spherical triangle is only 1 sec greater than the sum of the
angles of a plane triangle for a triangle having an area of approximately 75 sq
mi on the earth'ssurface, it is just reasonable that the errors caused by the
earth'sconsideredcurvatureonlyinprecisesurveysbeof large areas.
In this training manual, we will discuss
primarily the methods used in plane surveying rather than those used in
GEODETIC SURVEYING is a process of
surveying in which the shape and size of the earth are considered. This type of
survey is suited for large areas and long lines and is used to find the precise
location of basic points needed for establishing control for other surveys. In
geodetic surveys, the stations are normally long distances apart, and more
precise instruments and surveying methods are required for this type of
surveying than for plane surveying.
The shape of the earth is thought of as
a spheroid, although in a technical sense, it is not really a spheroid. In
1924, the convention of the International Geodetic and Geophysical Union adopted
41,852,960 ft as the diameter of the earth at the equator and 41,711,940 ft as
the diameter at its polar axis. The equatorial diameter was computed on the
assumption that the flattening of the earth caused by gravitational attraction
is exactly 1/297. Therefore, distances measured on or near the surface of the
earth are not along straight lines or planes, but on a curved surface.
Hence, in the computation of distances
in geodetic surveys, allowances are made for the earth'sminorand major
diameters from which a spheroid of reference is developed. The position of each
geodetic station is related to this spheroid. The positions are expressed as
latitudes (angles north or south of the Equator) and longitudes (angles east or
west of a prime meridian) or as northings and castings on a rectangular grid.
methods used in geodetic surveying are beyond the scope of this training manual
The purpose of a TOPOGRAPHIC SURVEY is
to gather survey data about the natural and man-made features of the land, as
well as its elevations. From this information a three-dimensional map may be
prepared. You may prepare the topographic map in the office after collecting
the field data or prepare it right away in the field by plane table. The work
usually consists of the following:
Establishing horizontal and vertical
control that will serve as the framework of the survey
Determining enough horizontal location
and elevation (usually called side shots) of ground points to provide enough
data for plotting when the map is prepared
Locating natural and man-made features
that may be required by the purpose of the survey
Computing distances, angles, and
Drawing the topographic map
Topographic surveys are commonly
identified with horizontal and/or vertical control of third-and lower-order
The term route survey refers to
surveys necessary for the location and construction of lines of transportation
or communication that continue across country for some distance, such as
highways, railroads, open-conduit systems, pipelines, and power lines.
Generally, the preliminary survey for this work takes the form of a topographic
survey. In the final stage, the work may consist of the following:
Locating the center line, usually marked
by stakes at 100-ft intervals called stations
Determining elevations along and across
the center line for plotting profile and cross sections
Plotting the profile and cross sections
and fixing the grades
Computing the volumes of earthwork and
preparing a mass diagram
Staking out the extremities for cuts and
Determining drainage areas to be used in
the design of ditches and culverts
Laying out structures, such as bridges
Locating right-of-way boundaries, as
well as staking out fence lines, if necessary
As mentioned earlier in this chapter,
SPECIAL SURVEYS are conducted for a specific purpose and with a special type of
surveying equipment and methods. A brief discussion of some of the special
surveys familiar to you follows.
LAND SURVEYS (sometimes called cadastral
or property surveys) are conducted to establish the exact location, boundaries,
or subdivision of a tract of land in any specified area. This type of survey
requires professional registration in all states. Presently, land surveys
generally consist of the following chores:
Establishing markers or monuments to
define and thereby preserve the boundaries of land belonging to a private
concern, a corporation, or the government.
Relocating markers or monuments legally
established by original surveys. This requires examining previous survey
records and retracing what was done. When some markers or monuments are
missing, they are reestablished following recognized procedures, using whatever
information is available.
Rerunning old land survey lines to
determine their lengths and directions. As a result of the high cost of land,
old lines are remeasured to get more precise measurements.
Subdividing landed estates into parcels of
predetermined sizes and shapes.
Calculating areas, distances, and
directions and preparing the land map to portray the survey data so that it can
be used as a permanent record. 6. Writing a technical description for deeds.
CONTROL SURVEYS provide "basic
control" or horizontal and vertical positions of points to which
supplementary surveys are adjusted. These types of surveys (sometimes termed
and traverse stations and the elevations of bench marks. These control points
are further used as References for hydrographic surveys of the coastal waters;
for topographic control; and for the control of many state, city, and private
Horizontal and vertical controls
generated by land (geodetic) surveys provide coordinated position data for all
surveyors. It is therefore necessary that these types of surveys use
first-order and second-order accuracies.
HYDROGRAPHIC SURVEYS are made to acquire
data required to chart and/or map shorelines and bottom depths of streams,
rivers, lakes, reservoirs, and other larger bodies of water. This type of
survey is also of general importance to navigation and to development of water
resources for flood control, irrigation, electrical power, and water supply.
As in other special surveys, several
different types of electronic and radio-acoustical instruments are used in
hydrographic surveys. These special devices are commonly used in determining
water depths and location of objects on the bottom by a method called taking
SOUNDINGS. Soundings are taken by measuring the time required for sound to
travel downward and be reflected back to a receiver aboard a vessel.