Chapter 2 Review Questions
Define error of closure, and give three ways in which it might be determined.
Error of closure is defined as the difference between a measured quantity and its true value (or) it can be defined as the difference between two independent measurements. 1. For example, consider a line from point A to point B. Measure the distance, the distance measured is 123.25 m. Now, measure the distance from point B to point A, then the distance will be 123.19 m. The error is the difference of the two measurements. 123.25-123.19=0.06 m 2. From other source like the previous governmental survey, if the actual distance was known to be 123.30 m. The error of closure would is defined as the difference between the average measured value and the known true value. (123.25+123.19)/2=123.22 m then, the error of closure would be 123.30-123.22=0.08 m 3. Another way to determine the closure is, from a series of independent measurements of the same quantity is to use the maximum anticipated error.
Accidental errors accumulate in proportion to the ________ of the ________ .
Square root of the number of measurements.
Briefly describe two different types of units for angular measurement.
1. Sexagesimal System: This system uses degrees, minutes, and seconds. In this system a complete rotation of a line (circle) is divided into 360 degrees of arc. One degree is dived into 60 minutes and 1 minute is further divided into 60 seconds or arc. 2. Centesimal System: This system uses the grad for angular measurement. A complete rotation is divided into 400 grads. The grad is sub divided into 100 parts called centi-grad and the centi-grad is further sub divided into 100 centi-centigrad. (1c=100cc)
Define the term blunder, and give three typical examples in surveying.
A blunder is a major mistake cause by human error. It's also called as a gross error. This is due to the carelessness of the surveyor, and the results in huge difference between the recorded and actual value. 1. Inattention or carelessness of the surveyor. 2. Lack of judgement or knowledge on the principle of surveying. 3. Misreading of a number on the surveying reading itself.
What is the basic difference between accuracy and precision? Is good precision always a guarantee of good accuracy?
Basic difference between the accuracy and precision in surveying is precision is the degree of perfection used in the survey and accuracy is the degree of perfection obtained in the results.
Define relative accuracy, and give two examples of how it is expressed or written. Which of your examples represents better accuracy?
For horizontal distances, relative accuracy is defines as the ratio of error of closure to the actual distance. It expressed as a ratio with unity as the first number. Example: If a distance of 1000 ft were measured with a closure of 0.5 fr, we can say that the relative accuracy of that particular survey is 0.5/1000 or 1/2000. For every 2000 ft, there is an error of 1 ft. The relative accuracy of a survey can be compared with a specified allowable standard of accuracy in order to determine whether the results of th survey are acceptable. Relative accuracy is calculated using the equation below: Relative Accuracy = 1:D/C
Is it good practice always to report all the digits displayed by a calculator in an answer to a problem? Why?
It's not a good practice to report all the digits displayed by a calculator in an answer to a problem. This is because such an answer may suggest more precision than necessary or even possible to be measure. Reporting too many digits will also be a sign that the surveyor is not experienced and does not completely understand the nature of measurement.
What does ppm refer to with (M.S. 31-32)
Parts per million
What is meant by data reduction?
Surveying includes both field and office work. Measurements that are made in the field are recorded in a field book and stored electronically. This data is generally used in preparation of deed description, topo map; for establishing location of points; determining area of land, or estimation of earthwork volume. This data should be transformed into a form that will be appropriate for the proposed application. This comprises mathematical computations in a process called data reduction.
What are the basic differences between a systematic error and an accidental error?
Systematic Errors: 1. The repetitive errors that are caused due to deficiencies in the surveying equipment, by the definite method of observation, or by some environmental factors. 2. Systematic error are constant in magnitude and direction or sign (either positive or negative) under same condition of measurement. If correction are not made, they usually have no affinity to cancel; they can gather to cause major differences between the measure and actual or true quantities. Accidental Errors 1. The difference between a true quantity that is free from blunder or systematic errors is defined as an accidental error. They occur in almost every measurement. They are somewhat small, inevitable error in observation that are usually beyond the control of the surveyor.
Define the term error as it pertains to surveying work. How does it differ from a blunder?
The difference between a measured quantity and its true value can be defined as ERROR. This is caused by defectiveness in the measuring instrument, wrong method of measurement, natural factors such as temperature, or variation in human observation. Difference between blunder and an error is blunders can be eliminated whereas errors cannot be eliminated, but can be minimized.
In a measured quantity, the number of certain digits plus one estimated digit is called the number of
The number of certain digits plus one estimated digit in a measured is called the number of significant figures.
To double the accuracy of a particular survey, must the number of observations or measurements be halved, doubled, or tripled? What must be done to triple the relative accuracy?
To double the accuracy of a particular survey, four times the number of original observations or measurements must be taken; to triple the relative accuracy, nine times as many observations must be made; and so on.
What is meant by the 95 percent error?
Using statistical formulas of surveying instruments and procedures, test and determine the probability of different ranges of random errors. The most probable error is that which has an equal chance of either being exceeded or not being exceeded in a particular measurement. It's sometimes called E50. For rating the surveying methods 95 percent error will be used.
When the same precision is used, would the relative accuracy of a long survey be the same as, better than, or worse than the accuracy of a shorter survey? Why?
With the same precision the relative accuracy of a long survey will be better that the accuracy of a shorter survey. A ratio with large second number or denominator implies better accuracy than a ratio with a small second number or denominator. As accidental errors, tend to increase in proportion to the square root of the distance measured and not to the actual distance itself. Therefore, when the same precision is applied, the relative accuracy of a long survey will be better than that of a short survey.
Indicate by A (accidental), S (systematic), or B (blunder) the type of error or mistake the following would cause: a) Swinging plumb bob while taping b) Using a repaired (spliced) tape c) Aiming the transit at the wrong point d) Recopying field data e) Surveying with a transit that is not level f) Reading a 9 for a 6 g) Reading the transit scale without a magnifying glass h) Working in poor light i) Not aiming the transit carefully j) Not focusing the transit carefully
a) Swinging plumb bob while taping - A (accidental error) b) Using a repaired (spliced) tape - B (blunder) c) Aiming the transit at the wrong point - B (blunder) d) Recopying field data - B (blunder) e) Surveying with a transit that is not level - S (systematic) f) Reading a 9 for a 6 - B (blunder) g) Reading the transit scale without a magnifying glass - B (blunder) h) Working in poor light - B (blunder) i) Not aiming the transit carefully - B (blunder) j) Not focusing the transit carefully - B (blunder)
Indicate by an A, S, or B whether the following. would cause accidental errors, systematic errors, or blunders: a) Using a level rod that is inaccurately graduated b) Having too long a sight distance between the level and level rod c) Carelessly centering the bubble of the spirit level in a level instrument when leveling d) Using a level instrument that is out of adjustment so that the line of sight is not horizontal when the bubble is centered e) Failing to check a reading f) Failing to correct for temperature when measurements are made with a steel tape on a very hot or cold day g) Failing to hold the level rod on the correct point h) Leveling when "heat waves" make it difficult to read the level rod i) Using the wrong end of the tape for measurement j) Working without glasses if you normally wear them
a) Using a level rod that is inaccurately graduated - S (systematic) b) Having too long a sight distance between the level and level rod - S (systematic) c) Carelessly centering the bubble of the spirit level in a level instrument when leveling - B (blunder) d) Using a level instrument that is out of adjustment so that the line of sight is not horizontal when the bubble is centered - S (systematic) e) Failing to check a reading - B (blunder) f) Failing to correct for temperature when measurements are made with a steel tape on a very hot or cold day - S (systematic) g) Failing to hold the level rod on the correct point - B (blunder) h) Leveling when "heat waves" make it difficult to read the level rod - S (systematic) i) Using the wrong end of the tape for measurement - B (blunder) j) Working without glasses if you normally wear them - B (blunder)