What are errors in surveying?

An error in surveying is defined as the difference between two or more values of an identical quantity. However, the estimates are never accurate and there will always be a degree of variability regardless of the research tool or method used. These differences are known as errors that need to be reduced or eliminated to maintain certain levels of accuracy. Even if you carefully follow the prescribed test procedures, the considerations may contain errors. 

Errors, by definition, are not the difference between the estimated value and its actual value. The actual value of the ratio is determined by taking the average value of the multiplication series ratings. Inspectors must be proficient in metalworking and knowledge test methods to reduce the error rate in each measure.

Sources of errors

There are the following different sources of errors:

• Natural errors
• Instrumental errors
• Personal errors

Natural errors

These are the effects of temperature, refraction, measurements obstructions, magnetic declination, and so on. The length of a steel tape, for example, fluctuates with temperature. Such causes of error are beyond the surveyor's control. Still, by taking preventative steps and using appropriate procedures for the environment, the mistakes can be kept below reasonable limits.

Instrumental errors

These are the consequence of the instrument's poor construction and adjustment. A few instances are inaccurate graduations on a steel tape and poor adjustment of a transit's plate levels. The impact of most instrumental mistakes can be brought within the necessary accuracy limits by applying appropriate adjustments and adopting appropriate field procedures.

Tool errors can be continuously reduced by periodic testing musical instruments, prisms, sticks, and three instruments. Annual maintenance contracts are purchased to ensure that test tools are regularly cleaned, measured, and prepared by an authorized professional. Occasionally during these travel services, data from the compiler operating system (firmware) will be replaced by the current version. It is equally important that equipment that is suspected to be intolerant is sent to the appropriate service center. The photogrammetry & survey category should be notified before shipping equipment for random adjustment, calibration, and adjustment.

Personal errors

These are caused by limits in human senses such as sight, touch, and hearing. A personal mistake, for example, is imprecisely bisecting an object by fixing the line of sight of transit while measuring angles.

Because any survey is only as accurate as of the tool/target set; a safe, secure standard tripod is important. The tripod should always be used to stabilize the backsight target when you place it on the control panel. When placing the tripod, firmly press the tripod feet on the ground. Place the tripod legs in an area that will reduce the value of moving near the tool. Reducing the movement near the tripod will decrease the chances of exploding. In windy conditions, you may need to put sandbags on top tripod feet to ensure stability. When setting up steep slopes, place two tripod legs on the sloping side. Periodically check the optical plummet to make sure that the tool is still focused on the point. Check the level bubble from time to time to confirm that the instrument is in a horizontal plane. The level bubble should hold one standing where the metal is well rotated with a complete rotation.

If you are taking an idea with a visual aid, the target center should align with the center of the reticle (or crosshair). For accurate results, every time you see a telescope go to the same part of the target. Open the ocular (or eyepiece) until the reticle is clearly focused. Then adjust the focus knot until the target becomes clearly defined within the viewing arena. When the viewer's eye moves in the background ocular, targeted, and reticle should not be removed from space with respect.

Types of errors

There are mainly three types of errors in surveying.

1. Systematic errors or cumulative errors
2. Mistakes
3. Accidental errors or compensating errors

Systematic error or Cumulative error

Systematic errors are always of the same magnitude and sign under specified similar conditions of measurement and can be classified as positive or negative depending on whether they make the result too large or too little. Because systematic errors have the effect of piling up in just one direction, they are also known as cumulative errors. They become dangerous if they do not come in observation. Systematic mistakes are discovered to obey a particular statistical or physical law. As a result, appropriate corrections for these faults may be identified and implemented. The surveyor must be fully aware of the numerous systematic mistakes likely to be encountered throughout his survey work. Systematic mistakes can always be found, and if elimination is not feasible, these errors may be analyzed, and their links to the factors that generate them can be deduced.

Mistakes

Inattention, inexperience, carelessness, poor judgment, or confusion in the observer's thinking are all examples of mistakes. An error that goes undiscovered has a significant impact on the end outcome. As a result, each value recorded in the field must be double-checked by field observation.

Accidental errors or compensating error

Compensating error or accidental errors remain after the exclusion of mistakes and systematic errors, and they arise for several causes beyond the observer's control. Compensating mistakes occur in one or both directions and are hence referred to as compensating errors. These errors are subject to the rule of probability, and the theory of error only applies to unintentional errors. Because they are random, these mistakes are also known as random errors. To estimate these mistakes, the probability theory is used. Accidental errors are generally of small magnitude, and they occur due to change in the atmospheric conditions, human limitations, imperfections in the instruments, and so on.

Precautions to minimize errors

The effects of these errors can be reduced to some extent by using the following precautions:

• Proper measurement of the research tool and objectives
• Anticipating foresight and looking back
• Incorporating appropriate environmental remediation features into the data collector
• Enter the appropriate metal length, target length, and prism offset data collector
• Occasionally evaluate the test material

If not corrected, these errors can accumulate and cause serious consequences for the difference between the estimated values. By keeping the instrument working correctly as well as abiding by particular testing steps, many systematic errors can be eliminated.

Context and Applications

This topic is important for professional exams in both undergraduate and postgraduate studies and in particular:

• Bachelors of Technology in Civil Engineering
• Masters of Technology in Civil Engineering

Practice Problems

1. Which of the following does not reflect the specialty in the law of accidental errors?

1. Negligible errors
2. Small errors
3. Large errors
4. Positive errors

Answer: Option a
Explanation: The official features of accidental errors include the tendency for small errors to become numerous, positive and common errors, and to make large errors impossible.

2. Which type of error can be removed by applying corrections to observed values?

1. Mistakes
2. Systematic errors
3. Accidental errors
4. Compensating errors

Answer: Option b
Explanation: Systematic errors can be removed by applying corrections to the observed values.

3. Which instrument is used for the measurement of both horizontal and vertical angles while surveying?

1. Vernier calipers
2. Plunger
3. Reading staff
4. Theodolite

Answer: Option d
Explanation: Theodolite is used for the measurement of both horizontal and vertical angles while surveying.

4. How can the errors due to eccentricity of outer and inner axes be terminated?

1. Reading both Vernier's and their means
2. Double sighting
3. Both a and b
4. None of the above

Answer: Option a
Explanation: By reading both Vernier's and calculating their means can eliminate the errors due to the eccentricity of inner and outer axes.

5. Which method from the following can be used to solve the three-point problem?

1. Tracing paper method
2. Lehman's method
3. Bessel's method
4. All of the above

Answer: Option d
Explanation: Tracing paper method, Lehman's method, and Bessel's method can be used to solve the three-point problem.