Surveying Field Work Surveyors determine the position of objects by measuring angles
and distances. The factors that can affect the accuracy of their observations
are also measured. They then use this data to create vectors, bearings,
co-ordinates, elevations, areas, volumes, plans and maps. Measurements are
often split into horizontal and vertical components to simplify calculation.
GPS and astronomic measurements also need measurement of a time component. Earlier distance was measured by using chains and standard sized sticks (in rural India) and all. Now a days EDM’s are used the most in every place . To measure horizontal distances, these chains or tapes were pulled taut to reduce sagging and slack. The distance had to be adjusted for heat expansion. Attempts to hold the measuring instrument level would also be made. It was sometimes used before to the invention of EDM where rough ground made chain measurement impractical.
Distance measurement:
 |  |
Angle measurement:
We can even measure
the horizontal angles by the modren equipment like theodlite , Totoal station
and so on etc., the image beside is a way which represents the way the horizontal angle is being
measured. For more detailed information watch the video below . It was a video on measuring a Horizontal angle of a plot using theodolite. It was from YouTube. Or for complete process of determining Horizontal angle follow the link..
Determining position:
Generally we locate a place by it’s Land mark or the
Geo-graphic location or by the one’s position on the earth’s surface
when no known positions are nearby is by astronomic observations. Since the advent of the GPS system, astronomic
observations are rare as GPS allows adequate positions to be determined over
most of the surface of the Earth....
Levelling:
It is
for one the reason for which Surveying is called imoprtant .Surveying not only
to measure distance th e distance and horizontal/vertical angles . It helps
greatly in leveling too. It is most useful at the places eith a slope or up and
downs.
Levelling can be done
in many ways these days. When
precise leveling, a series of measurements between two points are taken using
an instrument and a measuring rod. Differences in height between the
measurements are added and subtracted in a series to get the net difference in
elevation between the two endpoints.
GPS can also be used for levelling , but it is not that
accurate to be use . hence GPS sysytem for levelling used literaly less.It is
only used in extreme remote areas..
Errors and accuracy:
A basic tenet of surveying is that no measurement is
perfect, and that there will always be a small amount of error. There are three
classes of survey errors:
_ Gross errors or
blunders: Errors made by the surveyor during the survey. Upsetting the
instrument, misaiming a target, or writing down a wrong measurement are all
gross errors. A large gross error may reduce the accuracy to an unacceptable
level. Therefore, surveyors use redundant measurements and independent checks
to detect these errors early in the survey
. _ Systematic: Errors that follow a consistent
pattern.Examples include effects of temperature on a chain or EDM measurement,
or a poorly adjusted spiritlevel causing a tilted instrument or target pole.
Systematic errors that have known effects can be compensated or corrected.
_ Random: Random
errors are small unavoidable fluctuations. They are caused by imperfections in
measuring equipment, eyesight, and conditions. They can be minimized by
redundancy of measurement and avoiding unstable conditions. Random errors tend
to cancel each other out, but checks must be made to ensure they are not
propagating from one measurement to the next.
No comments:
Post a Comment