SURVEY PRINCIPLES: PRINCIPLE OF CONSISTENCY

Any ‘product’ is only as good as the most poorly executed part of it. It matters not whether that ‘product’
is a washing machine or open heart surgery, a weakness or inconsistency in the endeavor could cause a
catastrophic failure. The same may apply in survey principle, especially with control. For example, say the majority
of control on a construction site is established to a certain designed precision. Later one or two further
control points are less well established, but all the control is assumed to be of the same quality. When
holding-down bolts for a steelwork fabrication are set out from the erroneous control it may require a good
nudge from a JCB to make the later stages of the steelwork fit.
Such is the traditional view of consistency. Modern methods of survey network adjustment allow for
some flexibility in the application of the principle and it is not always necessary for all of a particular
stage of a survey to be of the same quality. If error statistics for the computed control are not to be made
available, then quality can only be assured by consistency in observational technique and method. Such a
quality assurance is therefore only second hand. With positional error statistics the quality of the control
may be assessed point by point. Only least squares adjustments can ensure consistency and then only if
reliability is also assured. Consistency and economy of accuracy usually go hand in hand in the production
of control.

MEANING AND SCOPE OF SURVEYING

The meaning and scope of surveying is in broad variety. As Surveying may be defined as the science of determining the position, in three dimensions, of natural and
man-made features on or beneath the surface of the Earth. These features may be represented in analogue
form as a contoured map, plan or chart, or in digital form such as a digital ground model (DGM).
In engineering surveying, either or both of the above formats may be used for planning, design and
construction of works, both on the surface and underground. At a later stage, surveying techniques are
used for dimensional control or setting out of designed constructional elements and also for monitoring
deformation movements.
In the first instance, surveying requires management and decision making in deciding the appropriate
methods and instrumentation required to complete the task satisfactorily to the specified accuracy and
within the time limits available. This initial process can only be properly executed after very careful and
detailed reconnaissance of the area to be surveyed.
When the above logistics are complete, the field work – involving the capture and storage of field data –
is carried out using instruments and techniques appropriate to the task in hand.
Processing the data is the next step in the operation. The majority, if not all, of the computation will
be carried out with computing aids ranging from pocket calculator to personal computer. The methods
adopted will depend upon the size and precision of the survey and the manner of its recording; whether
in a field book or a data logger. Data representation in analogue or digital form may now be carried out
by conventional cartographic plotting or through a totally automated computer-based system leading to
a paper- or screen-based plot. In engineering, the plan or DGM is used when planning and designing a
construction project. The project may be a railway, highway, dam, bridge, or even a new town complex.
No matter what the work is, or how complicated, it must be set out on the ground in its correct place and to its
correct dimensions, within the tolerances specified. To this end, surveying procedures and instrumentation
of varying precision and complexity are used depending on the project in hand.