These are caused due to variations in nature i.e., variations in wind, temperature, humidity, refraction, gravity and magnetic field of the earth.
These result from imperfection in the construction or adjustment of surveying instruments, and movement of their individual parts.
These arise from limitations of the human senses of sight, touch and hearing.
Types of Errors
Errors are traditionally been classified into three types.
Gross errors, also known as blunders or mistakes, are results from
- Carelessness on the part of observer in taking or recording reading
- Faults in equipment’s
- Adoption of wrong technique
The blunders or mistakes result into large errors and thus can easily be detected by comparing with other types of errors (generally small in value). The maximum permissible error in an observation is ± 3.29s (where s is the standard deviation of sample distribution) and is used to separate mistakes or blunders from the random errors. If any error deviates from the mean by more than the maximum permissible error, it is considered as a gross error and the measurement is rejected.
After mistakes have been detected and eliminated from the measurements, the remaining errors are usually classified either as systematic or random error depending on the characteristics of errors.
It is occur according to a system. These errors follow a definite pattern. Thus, if an experiment is repeated, under the same conditions, same pattern of systematic errors reoccur. These errors are dependent on the observer, the instrument used, and on the physical environment of the experiment. Any change in one or more of the elements of the system will cause a change in the character of the systematic error. Depending on the value and sign of errors in successive observation, systematic errors are divided into two types.
- Cumulative Error
- Compensating Error
Systematic errors are dealt with mathematically using functional relationships or models.
After mistakes are eliminated and systematic errors are corrected, a survey measurement is associated with random error only. This error is small and is equally liable to be plus or minus thus partly compensating in nature. Random errors are unpredictable and they cannot be evaluated or quantified exactly.