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2. Horizontal Distance Measurement
Log In Sign Up. Daniel Loh. Distances are not necessarily linear, especially if they occur on the spherical earth. In the present subject we will deal with distances in Euclidean geometric space, which we can consider a straight line from one point or feature to another. Pacing provides a simple yet useful way to make rough distance measurements.
All surveyors and construction technicians should know their own personal unit pace value. A typical measuring wheel used for making rough distance measurements.
Walk casually over m counting the number of steps. Work out the length of a casual step and use this instead. All standard in lengths — m, 50m, 30 m, 20 m.
Be careful, easily break. A steel tape in a convenient reel and typical tape markings. See also Figure d. A cut tape. A ft tape with graduations outside the ft length. In use, the graduated end and the add mark are kept forward, with the ft mark at the rear.Imma tataranni 2 quando esce
In laying out ft intervals, the mark and the zero mark are used. In measuring distances less than ft, for example, The rear chainman finds that the previous point marked on the ground comes between the and the ft mark.Bg addon repo
The head chainman reads the value of the backward graduation, that is, 0. A tape clamp handle. A plumb bob is one of the simplest yet most Courtesy of The Lietz Company important accessories for accurate surveying. The vertical cord transfers a position from the steel tape to the wooden stake in the ground. A nonmetallic m fiberglass tape.
How a loop breaks a tape. Methods of supporting a tape. Holding the plumb-bob cord pavement. Breaking tape over steeply sloping ground.
The positions along a measured line are called stations. Holding the plump-bob cord taut against the tack. Plumb-bob cord bent over tape.The distance between any two random points in three dimensional space is a spatial distance.
There are several methods of determining distance, the choice of which depends on the accuracy required, the cost, and other conditions. The methods in ascending order of accuracy are estimation, scaling from a map, pacing, odometer, tacheometry, taping, photogrammetry, and electronic distance measurement. The length of an individuals pace must be determined first. Pacing furnishes a rapid means of approximately checking more precise measurements of distance.
It is used on reconnaissance surveys and, in small-scale mapping, for locating details and traversing with the plane table.
Mileage recorder, odometer, and other methods Distance maybe measured by observing the number of revolutions of the wheel of vehicle. The mileage recorder attached to the ordinary automobile speedometer registers distance to 0.
Special speedometers are available reading to 0. The odometer is a simple device that can be attached to any vehicle and directly registers the number of revolutions of a wheel.
With the circumference of the wheel known, the relation between revolutions and distance is fixed. The distance indicated by either the mileage recorder or the odometer is somewhat greater than the true horizontal distance, but in hilly country a rough correction based on the estimated average slope may be applied.
Tacheometry Tacheometry includes stadia with transit and stadia rod; stadia with alidade, plane table, and rod; distance wedge and horizontal rod; and subtense bar and theodolite. Taping Taping involves direct measurement of the distance with steel tapes varying in length from 3ft 1 m to ft m.
Graduations are in feet, tenths, and hundredths, or metres, decimeters, centimeters, and millimeters. The precision of distance measured with tapes depends upon the degree of refinement with which measurements are taken. On the one hand, rough taping through broken country may be less accurate than the stadia.
Electronic distance measurement Recent scientific advances have led to the development of electro-optical and electromagnetic instruments which are of great value to the surveyor for accurate measurements of distances. Measurement of distance with electronic distance measuring EDM equipment is based on the invariant speed of light or electromagnetic waves in a vacuum. EDM equipment which can be used for traverse, triangulation, and trilateration as well as for construction layout is rapidly supplanting taping for modern surveying operations except for short distances and certain types of construction layout.
Choice of methods Most boundary, control, and construction surveys involving long lines and large areas can be performed most accurately and economically using modern EDM equipment. Where the distances involved are relatively short or specific construction layout requirements are present, taping the distances can be more practical.
Stadia is still unsurpassed for small topographic surveys and preliminary surveys for projects of limited extent. Each of the methods mentioned in the preceding sections has a field of usefulness.
On the survey for a single enterprise, the surveyor may find occasion to employ a combination of methods to advantage. TapesTapes are made in a variety of materials, lengths, and weights. Those more commonly used by the surveyor and for engineering measurements are the steel tapes, sometimes called the engineers or surveyors tape, and woven nonmetallic and metallic tapes.
Errors in measurement of Distances 1. Tape not standard length Imperfect alignment of tape Tape not horizontal Tape not stretch straight Imperfection of observation Variations in temperature Variations in tension. Mistakes in Measurement of Distances 1. Adding or dropping a full tape length. Adding a cm. Recording numbers incorrectly, example 78 is read as Reading wrong meter mark. Correction applied for measurement of distances 1. Normal Tension: It is the tension which is applied to a tape supported over two supports which balances the correction due to pull and due to sag.
The application of the tensile force increases the length of the tape whereas the sag decreases its length, the normal tension neutralizes both corrections, therefore no correction is necessary.There are many good ways to measure distances.
The method of measurement you use will depend on several factors: the accuracy of the result needed; the equipment you have available, to use; the type of terrain you need to measure. In the following sections, you will learn how to use the various methods of measurement.
Table 1 will also help you to compare these methods and to select the one best suited to your needs. TABLE 1. In italics, equipment you can build yourself, as explained in text. Calculating perimeter lengths 5.
The perimeter of an area is its outer boundary. The length of the perimeter of regular geometrical figures can be calculated from the mathematical formulas given in Annex 1at the end of this manual.
To measure short distances, use a measuring stick called a ruler, 4 to 5 m long. You can make your own by following the steps below. A ruler is particularly useful for measuring horizontal distances on sloping ground.
Making your own ruler 2. Get a piece of wood which is straight and flat. It should be about 5 cm wide, and a little more than 4 m long. You can also use a shorter length, if the distance you are going to measure is shorter. It is best to use a planed piece of wood, but if you cannot get one you may use a straight wooden pole. If you use a pole, you should plane at least one of its surfaces. You should now add graduations to it.
Graduations are marks which show exact measurements, in centimetres, decimetres, metres, etc. To do this, you need to get two ready-made measuring tapes, such as the 2 m ribbon tapes that tailors use. Glue one of these measuring tapes onto the planed face of your piece of wood.
Take care to align the zero mark of this tape with one of the ends of the piece of wood.Basic field operations performed by a surveyor involve linear and angular measurements.
The highway surveyor must be adept at making the required measurements to the degree of accuracy required. Various types of engineering works require various tolerances in the precision of the measurements made and the accuracies achieved by these measurements.
The use of common sense and development of good surveying practice in all phases of a survey cannot be overemphasized. All conditions that may be encountered in the "real world" during the actual field survey cannot be covered in any manual. A manual may specify certain techniques, such as a certain number of repeated operations, to achieve a required accuracy.Bms anagni vendita
The surveyor must then often use judgment based on the equipment being used and the field conditions encountered, to modify those techniques. Some field conditions heat waves or wind for example may make it impossible to perform some operations to a consistent degree of accuracy. Accuracy is the degree of conformity with a standard or accepted value.
Accuracy relates to the quality of the result. It is distinguished from precision that relates to the quality of the operation used to obtain the result. The standard used to determine accuracy can be:. Although they are known to be not exact, higher order NGS control points are deemed of sufficient accuracy to be the control for all other less exact surveys.
Precision is the degree of refinement in the performance of an operation procedures and instrumentation or in the statement of a result. It is a measure of the uniformity or reproducibility of the result. The accuracy of a field survey depends directly upon the precision of the survey. Although through luck compensating errors, for example surveys with high order closures might be attained without high order precision, such accuracies are meaningless.
Therefore, all measurements and results should be quoted in terms that are commensurate with the precision used to attain them. Similarly, all surveys must be performed with a precision that ensures that the desired accuracy is attained. However, surveys performed to a precision that excessively exceeds the requirements are costly and should be avoided. Statistically speaking, field observations and the resulting measurement are never exact. Any observation can contain various types of errors.
Often some of these errors are known and can be eliminated by applying appropriate corrections. However, even after all known errors are eliminated, a measurement will still be in error by some unknown value.
To minimize the effect of errors, the surveyor has to use utmost care in making the observations and utilizing only calibrated equipment.
However, a measurement is never exact, regardless of the precision of the observations. Although this manual contains many guidelines and standards, the ultimate responsibility for providing surveys that meet desired accuracies remains with the field personnel. To fulfill this responsibility, the crew chief and his or her assistants must understand errors, including but not limited to:. Many textbooks on surveying refer to a blunder as a gross error.
One can easily make a case for a blunder to be considered an error. However, a blunder is really an unpredictable gross mistake made by the surveying team. It is not a hidden error that will go unnoticed, but usually it becomes apparent that something is wrong with the measurements. Examples of blunders are:.
Blunders are caused by carelessness, misunderstanding, confusion, or poor judgment. They are, for the most part, avoided by alertness, common sense, and good judgment. Small blunders are more difficult to detect and correct especially if the number of redundant measurements is too small. Therefore, surveys must be carried out with sufficient redundancy to prevent a blunder from going undetected.
All blunders must be eliminated prior to correcting and adjusting a survey for errors. Error is the difference, after blunders have been eliminated, between a measured or calculated value of a quantity and the true or established value of that quantity.To browse Academia.
Skip to main content. Log In Sign Up. Surveying Problem Solving. Saied Albayya. Dr A M Chandra Distance m. No part of this ebook may be reproduced in any form, by photostat, microfilm, xerography, or any other means, or incorporated into any information retrieval system, electronic or mechanical, without the written permission of the publisher. All inquiries should be emailed to rights newagepublishers.
It aims at helping the students understand surveying more comprehensively through solving field related problems. Each chapter of the book commences with a summary of basic theory and a range of worked out examples making it very useful for all undergraduate and postgraduate courses in surveying. Alternative solutions to the problems wherever possible, have also been included for stimulating the budding minds.
A number of objective type questions which are now a days commonly used in many competitive examinations, have been included on each topic to help the readers to get better score in such examinations. At the end, a number of selected unsolved problems have also been included to attain confidence on the subject by solving them. The practicing engineers and surveyors will also find the book very useful in their career while preparing designs and layouts of various application-oriented projects.
Constructive suggestions towards the improvement of the book in the next edition are fervently solicited. The author expresses his gratitude to the Arba Minch University, Ethiopia, for providing him a conducive environment during his stay there from Sept.
The author also wishes to express his thanks to all his colleagues in India and abroad who helped him directly or indirectly, in writing this book. A LEE 1. Direct Method Using a Tape 20 2. Error in Pull Correction due to Error in Pull 23 2. Error in Sag Correction due to Error in Pull 23 2.
Tacheometric or Optical Method 26 2. Subtense Tacheometry 27 2. Effect of Staff Vertically 27 2. Accuracy in Vertical Angle Measurements 36 3. Levelling 59 3. Datum 59 3. Level Line 59 3. Direct Differential or Spirit Levelling 60 3. Comparison of Methods and their Uses 63 3.
Loop Closure and its Apportioning 64 3. Reciprocal Levelling 64 3. Trigonometric Levelling 65 3. Sensitivity of a Level Tube 67 3. Two-Peg Test 67 3. Eye and Object Correction 68 4. The Theodolite 89 4. Adjustment of Observations 5.Horizontal distances are distances laid on the ground or earth surface. We will discuss following topics in the chapter:. Wheel tape does not provide high precision which is aroundbut provides a convenient way to conduct fast measurement on a path or road including its curves.
A lot have to be done to conduct measurement in an appropriate way to obtain precision expected. To achieve a high level of accuracy one must avoid several potential random and systematic errors further explained. If 1 m shift on distance of m is not exceeded, then there are no needs to worry much about the error of the result. There are tools available to check that tape or its start and end point is aligned into horizontal level.
Such tool is, for example, "hand level", which has to be set up with the built-in spirit bubble. Pulling with proper force The tape has to be pulled with proper force, which is stated by the manufacturer. Let us make an example, that instead of pulling by proper force of 20 N 2 kg tape is pulled by 50 N. At 15 K diversion expansion will be 0.
The factor will be even more of interest if a survey is conducted in winter. Stations are temporary objects established to conduct measurement. They can be short-time lived, for purposes of measuring distances only, or long-time lived, based for further measurements. Marks on the ground must be made clear, visible and rigid. The marks are often established in order to conduct further measurements, e.Correcting Distance Measurements
In such cases their exact position will be found later using calculations. Marks will be established. Marks should be done by scratch, a color label can be used outside.Monetarism was first championed by
Plumb bob is used over the tape against mark as explained on picture. EDM is designed to make a measurement of distances of up to tens of kilometers. There are two categories of inaccuracy with EDM:.
2. MEASURING HORIZONTAL DISTANCES
Using EDM for short distances is not appropriatenot accurate, because the error is mostly fixed per measurement. The early EDM instruments could measure long distances with an accuracy of about 5 parts per million i. Nowadays there are also many types of accurate and compact EDM instruments integrated with an electronic theodolite and known generically as a Total Station. Generally speaking, EDMI measures distances.
Does not measure horizontal distance. Prism is equipment used together with EDM instrument. It serves to reflect back a signal usually infrared light or microwaves 3 to 35 GHz send by instrument. The larger prism is, the longer distances can be measured: multiplied prisms are being used for long distances. Scheme above shows in 2D space two mirrors connected at the right angle.
When beam reaches first mirror, it leaves the mirror under the same angle and continues to the second mirror where the same happens. If we study angles within the picture a little, we will see that the result is not depending on the angle of origin within some borders : beam coming in leaves out to the direction of origin. Init was first commercially available electro-optical distance meter. Its total weight is near kg. It is capable of measuring distances up to 50 km.
The observations can be made in nights only. List of chapters. Horizontal measurements Horizontal distances are distances laid on the ground or earth surface. In some circumstances pacing may be sufficient technique.Click here to return to the page you were visiting.
The worst-case predictions regarding the effects of global warming are the most likely to be true, a new study published this week has warned. Ken Caldeira, an atmospheric scientist at the Carnegie Institution for Science, who co-authored the study told The Independent. Since the Earth's climate system is incredibly complex, different scientists have put forward different models to determine how fast the planet is warming. This has resulted in a range of predictions, some more dire than others.
The new study, published in the academic journal "Nature", aimed to determine whether the upper or lower-end estimates are more reliable. Caldeira and co-author Dr. Patrick Brown looked at models that proved to be the best at simulating climate patterns in the recent past. They reasoned that these models would present the most accurate estimates. According to the researchers' conclusions, models with higher estimates are more likely to be accurate, meaning the degree of warming is likely 0.
Scientist that weren't involved with the research have come out in support of the findings as well. Professor Collins explained that the new study "breaks the issue down into the fundamental building blocks of climate change. President Donald Trump have dismissed such claims. However, with more and more research backing worst-case predictions, complete dismissal of such findings becomes increasingly difficult.
This study in particular addresses one key point climate change deniers often seize upon: the uncertainty that comes with so many different climate models. RELATED: Climate disaster map shows Georgia as second most apocalyptic state"This study undermines that logic," Dr.
Brown told MIT Technology Review. Cadeira's study also comes on the heels of a dire warning issued by more than 15,000 scientists from around the world last month. The scientists warned that quick and drastic actions should be undertaken by society to address the threat to Earth.
President Donald Trump said in June that he would pull the U. Since then, Nicaragua agreed to sign the agreement in October, and Syria followed in November. Instead of addressing greenhouse gas emissions as the Paris accord requires, the White House said it "will promote coal, natural gas and nuclear energy as an answer to climate change," a decision scientists around the globe have warned against. RELATED: California wildfires force thousands to evacuate: Live updates Sign up for free e-newsletters to get more of AJC delivered to your inbox.
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