Opportunity for error exists in everything we do as humans and in every piece of equipment we may use for bc survey. This is especially true in surveying and understating, realizing and dealing with error is an absolute necessity.
An error is a difference between a measured or observed value and the “true” value. Every measurement contains some magnitude of the error. Errors are minimized and kept at an acceptable level by an experienced and skilled survey technician, skillful techniques, and using equipment that is appropriately suited to the task at hand, maintained and accurately calibrated. For the purpose of calculating errors, the “true” value of a dimension is determined statistically after multiple measurements have been taken.
Sources of errors fall into three main categories:
- Natural Errors caused by atmospheric conditions such as weather, temperature, the wind, refractions, and unmodelled gravity effects.
- Instrument errors caused by imperfections in the constructions and adjustment of the surveying equipment being used.
- Human error’s caused by the inability of the survey technician to make exact observations due to limitations of human sight, touch, and hearing.
Classifications of Error:
- Mistakes are sometimes called gross errors, but should not be classed at errors at all. They are blunders, often resulting from fatigue or an inexperienced surveyor. Because mistakes are typically large they are usually easy to spot and deal with.
- Systematic errors are defined as errors for which the magnitude and algebraic sign can be determined. The fact that these errors can be determined allows for the surveyor to calculate and then apply a correction to the measurement to reduce its effect. It is doubtful, however, whether the entire effect of the systematic error is ever entirely eliminated. Careful calibration of all equipment is an essential part of controlling and eliminating the systematic error. An example of systematic errors is the effect of temperature on a steel tape. If the temperature is warm the tape expands and the length of the tape increases, if the temperature is cold the steel tape shrinks and the length is reduced.
- Random errors are associated with the skills and vigilance of the surveyor. Random error is introduced into each measurement mainly because no human can perform perfectly. Random errors should be small and there is no procedure that will compensate for or reduce any one single error. Random errors, possibly due to sloppy work, also tend to cancel out giving the appearance of accurate work despite being highly inaccurate.
For more than 20 years, Okanagan Survey & Design has specialized in providing professional, cost-effective technical solutions for projects. Okanagan Survey & Design provides construction and engineering surveying services only. Contact us with any questions about your project needs.