INTRODUCTION TO ENGINEERING SURVEY

DEFINITION :

The art and science of making such

measurements as are necessary to

determine the relative position of points above, on, or beneath the surface of

the earth, or to establish such points in a specified position

Geodetic Surveying

• a  process  of surveying in which the shape and size of the earth are considered.
• 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.
• the stations are normally long distances apart, and more precise instruments and surveying methods  are  required  for  this  type  of  
•     surveying

Plane Surveying

oBranch of surveying in which the surface of the earth is considered a plane surface

oare the most commonly practised method of surveying and treat the earth as a flat or "plane" surface.

ofor small-scale surveys in limited areas, the curvature of the earth has no effect on the results, thus the computations and results can be referenced to a plane or flat surface.

used for the determination of legal boundaries, for engineering surveys for the construction of buildings and roads and for small-scale topographic surveys

KINDS OF SURVEYS

oTopographic surveys

Collect field data to prepare topographic maps

oHydrographic surveys

Map shorelines of water bodies, chart

bottom areas of streams, lakes, harbors,

etc., measure flow of rivers, assess other

issues related to navigation and water resources

oAerial surveys (photogrammetry)

Use photographs mounted in specially

designed planes

Construction surveys

Performed during building of structure or project to fix elevations, horizontal position, and dimensions

oControl surveys

 Provide basic horizontal and vertical position data for engineering mission

BASIC SURVEY
MEASUREMENTS: DEFINITIONS

oDirection of gravity used as

    reference direction

Vertical – means direction of gravity

Horizontal – means direction

                   perpendicular to gravity

DEFINITIONS

oLevel surface (geoid)

     Continuous surface that is at all points perpendicular to the direction of gravity. Can be thought of as the surface of large body of water at complete rest (unaffected by tides, etc.)

oElevation

    Vertical distance above or below a given reference level surface

oDifference in elevation

     Vertical distance between two level surfaces containing the two points


SOURCES OF ERRORS

oNatural errors : caused by variations in wind, temperature, humidity, atmospheric

    pressure, atmospheris refraction, gravity and magnetic decliniation

oInstrumental errors : imperfection in the construction or judgement of

    ınstruments and from the movement of individual parts

oPersonal errors : arise from limitations of sight and touch.

TYPES OF ERRORS

oSystematic error

-Occur according to a system which can be

expressed mathematically

-Magnitude and sign can be determined

-Follow definite pattern

-Can be caused by observer, instrument,

environment

oRandom error

-Error left after systematic error removed

-May tend to cancel themselves