ERRORS
Every measurement contains errors of unknown magnitude due to several reasons and hence no measurement in surveying is exact . A surveyor should, therefore, understand thoroughly the nature of the sources and behaviour of the errors . which may affect the results. A knowledge of the errors and necessary to maintain a required precision
TRue error defined as the differene between true value and measured value .
SURVEYING ERROR & TYPE
Sources of Error
The sources of error in surveying may be classified as natural, instrumental, and personal
Natural errors :These result from the temperature, refraction, obstacles to measurements, magnetic declination, etc. For example, the length of a steel tape varies with changes in temperature. Such sources of error are beyond the control of the surveyor, but by taking precaution and adopting suitable methods the errors can be minimize within permissible limits
- Instrumental errors :These result from the imperfect construction and adjustment of the instrument.
- The incorrect graduations of a steel tape effects improper adjustment of the plate levels of a transit are a few examples.
Personal errors :These arise from the limitations of the human senses such as sight, touch and hearing For example, improper bisecting of the object by fixing the line of sight of a transit while measuring angles is a personal error
Types of Errors
Errors in a measurement may be positive or negative. The former occurs ifthe measurement is too large and the latter if too small. Errors are classified assystematic errors and accidental errors.
Systematic errors : A systematic error follows a definite mathematicall or physical law . Therefore correction can aly determined and applied.also known as cumulative error
- Accidental errors These are the errors due to a combination of causes and are beyond the control of surveyor. It can be plus or minus. Calibration of a chain is an example of an accidental erro
