Levelling Surveying Terminology in Advanced Surve

Levelling

1. Levelling Surveying Terminology Team 4

2. Content Introduction Levelling Surveying Terminology and Datum Hight of Collimation, Rise and Fall Summary Levelling Surveying Terminology Back Sight, Fort Sight and Intermediate Sight Flying Level

3. Back Ground History The history of surveying  dates back to ancient times, with a recorded land register in Egypt in 3000BC , and re-establishment of farm boundaries following floods of the Nile River and construction of the Great Pyramid of Giza recorded about the same time. Surveys have not always been a standard component of research, in fact, they have been in use for less than 200 years. The earliest known survey was conducted in  1834 , by the Statistical Society of London. Levelling Surveying Terminology

4. Introduction Surveying is the technique of determining the relative position of different features on, above or beneath the surface of the earth by means of direct or indirect measurements and finally representing them on a sheet of paper known as plan or map. 4 Levelling Surveying Terminology

5. Objectives of Surveying To determine the relative position of any objects or points of the earth. To determine the distance and angle between different objects. To prepare a map or plan to represent an area on a horizontal plain. To develop methods through the knowledge of modern science and the technology and use them in the field. To solve measurement problems in an optimal way. Presentation Title

6. What is leveling Surveying Terminology? Levelling is defined as the process of determining the relative heights \ elevations of points \ objects on the earth’s surface. Levelling Surveying Terminology

7. Datum A datum is a reference point or surface against which position measurements are made and an associated model of the shape of the earth for computing positions. An arbitrary horizontal plane of reference from which all vertical dimensions are measured. The most widely used datum surface is the Mean Sea Level, M.S.L. There are many other day to day examples such as temperature, pressure, distance, etc . Levelling Surveying Terminology

8. Datum There are two kinds of datum: Horizontal datum is mostly used in coordinate system on the earth surface such as latitude and longitude. E.g., for maps Vertical datum is mostly in determining the elevations or height. E.g., in levelling on the construction site Levelling Surveying Terminology

9. Levelling Machine Tripod Levelling rod Ranging Rod Plumb Bob Levelling Instruments Levelling Surveying Terminology

10. Back Sight The First reading taken at the staff rod after setting the instrument is called Back Sight or (B.S). Back Sight or B.S is generally taken on the point of known reduced level as on the benchmark or a change point. Reduced Level = Line of Collimation + Back Sight Levelling Surveying Terminology

11. Fore Sight The last reading taken at the survey line or the last reading before shifting the instrument is called Fore Sight or (F.S) It is the staff reading taken on point whose RL is to be determined. This sight is considered as negative and deduced from line of collimation to determine RL of the point. Reduced Level = Line of Collimation – Fore Sight Levelling Surveying Terminology

12. Intermediate Site The reading taken between back sight and fore sight is called Intermediate sight or (I.S) These are the points between Foresight and back sight whose RL is determined by the method already mentioned above in FS. Also called inter-sight readings. Reduced level = line of collimation - Intermediate sight Levelling Surveying Terminology

13. Height of Collimation Height of collimation is the height of horizontal plain through the telescope. Height of Collimation = Benchmark + Staff Reading Levelling Surveying Terminology

14. Rise and Fall It is the method of calculating the difference in elevation between consecutive points in levelling works. Rise = Positive (+) Fall = Negative (   Levelling Surveying Terminology

15. Height of Collimation (HCM) More Rapid Saves a considerable time and labour . Cannot Check Error is unnoticeable Different Between (H.C.M) and (R.F.M) Rise and Fall (REM) Slow Take more time and labour Can Check Error is noticeable

16. Ordnance Benchmark Ordnance benchmark is permeant benchmark, reference from mean sea level. If we know exact height, it is easy to find out next BM. It is used as start point of levelling or to check a point at the end. Levelling Surveying Terminology

17. Temporary Bench Mark Temporary Bench Mark is to control level. In site, it is used as a mark on the tree, Nails in road, marks on channel as temporary Bench Mark. Levelling Surveying Terminology

18. Flying Level Fly Levelling also known as differential levelling is a very approximate form of levelling. It is conducted when the benchmark is very far from the workstation. Levelling Surveying Terminology

19. Purpose Of Levelling Surveying To find the elevations of points on the earth’s surface for topographic maps. For design of highways, railways, canals, etc. For locating grade lines. For laying out of construction projects. For locating excavating levels To determine the drainage characteristics of an area Determination of volumes of earthwork for roads, railways etc. Levelling Surveying Terminology

20. Summary The purpose of levelling is to find out the elevation of the proposed site with the help of two methods that is already mentioned in advance- rise and fall method and line of collimation method. Furthermore, we need to be in touch with the levelling instruments, how the back sight, foresight, datum and benchmark are intertwined and work. 21 Levelling Surveying Terminology