SURVEYING AND GEOINFORMATICS

SURVEY PRINCIPLES: PRINCIPLE OF CONSISTENCY

2012-08-20T17:23:00.000-07:00

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

2012-08-11T22:42:00.000-07:00

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.

SURVEYING: PRINCIPLE OF ECONOMY AND ACCURACY

2012-08-11T16:45:00.000-07:00

Surveys are only ever undertaken for a specific purpose and so should be as accurate as they need to be, but
not more accurate. In spite of modern equipment, automated systems, and statistical data processing the
business of survey is still a manpower intensive one and needs to be kept to an economic minimum. Once
the requirement for a survey or some setting out exists, then part of the specification for the work must
include a statement of the relative and absolute accuracies to be achieved. From this, a specification for
the control survey may be derived and once this specification has been achieved, there is no requirement
for further work.
Whereas control involves working from ‘the whole to the part’ the specification for all survey products
is achieved by working from ‘the part to the whole’. The specification for the control may be derived from
estimation based upon experience using knowledge of survey methods to be applied, the instruments to
be used and the capabilities of the personnel involved. Such a specification defines the expected quality of
the output by defining the quality of the work that goes into the survey. Alternatively a statistical analysis
of the proposed control network may be used and this is the preferable approach. In practice a good
specification will involve a combination of both methods, statistics tempered by experience.

CONTROL NETWORK IN SURVEYING

2012-08-11T15:10:00.001-07:00

A control network is the framework of survey stations whose coordinates have been precisely determined
and are often considered definitive. The stations are the reference monuments, to which other survey work
of a lesser quality is related. By its nature, a control survey needs to be precise, complete and reliable and
it must be possible to show that these qualities have been achieved. This is done by using equipment of
proven precision, with methods that satisfy the principles and data processing that not only computes the
correct values but gives numerical measures of their precision and reliability.
Since care needs to be taken over the provision of control, then it must be planned to ensure that it
achieves the numerically stated objectives of precision and reliability. It must also be complete as it will
be needed for all related and dependent survey work. Other survey works that may use the control will
usually be less precise but of greater quantity. Examples are setting out for earthworks on a construction
site, detail surveys of a greenfield site or of an as-built development and monitoring many points on a
structure suspected of undergoing deformation.
The practice of using a control framework as a basis for further survey operations is often called ‘working
from the whole to the part’. If it becomes necessary to work outside the control framework then it must
be extended to cover the increased area of operations. Failure to do so will degrade the accuracy of later
survey work even if the quality of survey observations is maintained.
For operations other than setting out, it is not strictly necessary to observe the control before other
survey work. The observations may be concurrent or even consecutive. However, the control survey must
be fully computed before any other work is made to depend upon it.

BASIC MEASUREMENTS IN SURVEYING

2012-08-11T14:39:00.000-07:00

Surveying is concerned with the fixing of position whether it be control points or points of topographic detail and, as such, requires some form of reference system. The physical surface of the Earth, on which the actual survey measurements are carried out, is not mathematically definable. It cannot therefore be used as a reference datum on which to compute position. Alternatively, consider a level surface at all points normal to the direction of gravity. Such a surface would be closed and could be formed to fit the mean position of the oceans, assuming them to be free from all external forces, such as tides, currents, winds, etc. This surface is called the geoid and is defined as the equi potential surface that most closely approximates to mean sea level in the open oceans.An equi potential surface is one from which it would require the same amount of work to move a given mass to infinity no matter from which point on the surface one started. Equipotential surfaces are surfaces of equal potential; they are not surfaces of equal gravity. The most significant aspect of an equipotential surface going through an observer is that survey instruments are set up relative to it. That is, their vertical axes are in the direction of the force of gravity at that point. A level or equipotential surface through a point is normal, i.e. at right angles, to the direction of gravity. Indeed, the points surveyed on the physical surface of the Earth are frequently reduced, initially, to their equivalent position on the geoid by projection along their gravity vectors.
The reduced level or elevation of a point is its height above or below the geoid as measured in the
direction of its gravity vector, or plumb line, and is most commonly referred to as its height above or below
mean sea level (MSL). This assumes that the geoid passes through local MSL, which is acceptable for most
practical purposes. However, due to variations in the mass distribution within the Earth, the geoid, which
although very smooth is still an irregular surface and so cannot be used to locate position mathematically.

CLASSIFICATION OF SURVEYING BASED INSTRUMENT

2010-01-25T09:01:00.000-08:00

Based on instruments used surveying can be classified as:

1) Chain survey

2) theodolite survey
5) compass survey
4) tacheometry survey
5) plain survey
6) aerial and photographic survey
7) Modern survey using electionic distance meters and total station

CLASSIFICATION OF SURVEYING BASED ON THE TERAIN

2010-01-25T08:55:00.000-08:00

Survey may be classified based on the terrain as land survey,astronomical survey and marine or hydraulic survey. When we say Land Survey, It also involves measurement of various objects on and above the surface of the earth. This type of survey can be hereby classified as given below:
(i) Topographic Survey: It is meant for plotting natural features like rivers, lakes, forests and hills as well as man made features like roads, railways, towns, villages and canals.
(ii) Cadestal Survey: It is for marking the boundaries of municipalities, villages, talukas, districts, states etc. The survey made to mark properties of individuals also come under this category.
(iii) City Survey: The survey made in connection with the construction of streets, water supply and sewage lines fall under this category.
(iii) Hydrographic Survey. Survey conducted to find depth of water at various points in bodies of water like sea, river and lakes fall under this category. Finding depth of water at specified points is known as sounding.
(iv) Astronomical Survey. Observations made to heavenly bodies like sun, stars etc., to locate absolute positions of points on the earth and for the purpose of calculating local time is known as astronomical survey.
(v) Geological Survey: A geological survey is the systematic investigation of the subsurface of a given piece of ground for the purpose of creating a geological map or model. A geological survey employs techniques from the traditional walk-over survey, studying outcrops and landforms, to intrusive methods, such as hand angering and machine driven boreholes, to the use of geophysical techniques and remote sensing methods, such as aerial photography and satellite imagery.

STAGES OF SURVEY

2010-01-25T08:47:00.000-08:00

recognizance
field work
office work

CHECKS ON FIELD
leveling the field (bench mark)
submission of the angles
linear errors

survey procedures

2010-01-25T08:44:00.000-08:00

planning
collecting measurements
processing measurements
drawing up

BASIC PRINCIPLES ON SURVEYING

2010-01-23T09:04:00.000-08:00

Every profession must be founded upon sound practice and in this engineering surveying is no different.
Practice in turn must be based upon proven principles. This section is concerned with examining the
principles of survey, describing their interrelationship and showing how they may be applied in practice.
Most of the principles below have an application at all stages of a survey and it is an unwise and
unprofessional surveyor who does not take them into consideration when planning, executing, computing
and presenting the results of the survey work. The principles described here have application across the
whole spectrum of survey activity, from field work to photogrammetry, mining surveying to metrology,
hydrography to cartography, and cadastral to construction surveying.Survey is act or science of making measurement of relative position of points on land, above and below the earth by making linear direction and representation