What is meant by surveying?Surveying is a technique of making all the essential measurements for determining the relative position of points on or beneath the Earth’s surface by measuring the horizontal distances, elevations, directions, and angles. Surveying helps in analyzing and recording all the characteristics of a terrain and designing plans or maps for constructions such as bridges, highways, channels, dam, and pipelines. Surveys will always be conducted to determine the location of the site and its surrounding before the commencement of any engineering project. The aim of surveying is typically used to obtain topographic information to prepare a map which shows the relative positions of the objects on the surface of the earth. 2.
What are the principles of surveying?The fundamental principles of surveying are : I. to work from the whole to the part. II.
to locate a new station through linear or angular measurements from fixed reference points. According to the first principle, the whole surveying area is first enclosed by forming a network of control points (stations) with high precision. These points are established by triangulation. The surveying area is then divided into numerous large triangles with the greatest accuracy.
These large triangles are further divided into small triangles which are surveyed with less accuracy as figure 3.2.1. The objective of working from the whole to the part is to control minor errors and to prevent the accumulation of errors so that the aftermath of errors of one section does not affect the rest.
Figure 3.2.1 According to the second principle, after deciding the position of a new station, it can be located by means of linear or angular measurement from at least two fixed reference points. Linear measurement is actually horizontal distance which can be measured by using tape. Angular measurement refers to the horizontal angle which can be measured by using theodolite.
3. How many links are provided in a 20-meter metric chain?Metric chains come in many lengths such as 5, 10, 20 and 30 meters. However, the most commonly used is 20-meter metric chain. Tallies are provided at every 2 meters of the chain for easy reading of measurements. Every link of this type of chain is 0.
2 meters. Therefore, 100 links are provided in a 20-meter metric chain as figure 3.3.1. Figure 3.3.1 4. Differentiate between ranging rod and offset rod.
Ranging rods and offset rods are long poles that made up of wood and metal and painted with red and white or black and white alternately as the figure 3.4.1.
These rods are used to range some intermediate points in a survey line and set out straight lines on the field when the survey line is long. The only difference between ranging rod and offset rod is the length. Ranging rods and offset rods are commonly 3 meters long. Ranging rods of greater length than 3 meters are called ranging poles that are used in a very long survey line, however, the ranging poles are only available up to 8 meters long. Offset rod has no flag attached to the top of it, but a flag with yellow or red or white color will be attached to the top of a ranging pole for clear visibility when the length of survey lines is long. Offset rod is typically used to measure the offset of short lengths from the survey line and there are two narrow slits at right angles to each other which are used to set right angles.
Figure 3.4.1 5.
Define the terms baseline, tie line, and check line.A baseline is the most significant and the longest chain line which about passes through the center of the survey field as figure 3.5.1. This line will always be plotted first before the framework of triangles are built on it.
All the other measurements that show the details of the work will be taken with respect this line. Therefore, the measurement of the baseline must be accurate as the accuracy of the whole survey work depends on it.A tie line is a line that joins some fixed points called stations to the main survey lines as figure 3.
5.1. It helps to locate the interior details and accuracy of surveying. The main objective of running a tie line is to get the information of nearby objects.A check line is a line that connecting the main station to a subsidiary station on the opposite site is connecting to the subsidiary station as figure 3.5.
1. Measurement of a check line will always be done to examine the accuracy of the framework. The length of a check line that is measured on the ground should be matched with its length on the plan.
Figure 3.5.1 Subsidiary Stations : F, G, H, L Main Survey Stations : A,B,C,D,E Main Survey Lines : AB, BC, CD, DE, EA Base Line : BE Check Lines : HL, MN Tie Lines : AF, GC 6. What is meant by perpendicular and oblique offset?The measurements which are not made at right angles to the survey line are called oblique offsets as figure 3.6.
1. The measurements are taken at right angle to the survey line called perpendicular offsets as figure 3.6.1. Figure 3.
6.1 7. What is the usage of Total Station?Total Station is an instrument that is integrated with distance measuring instrument (EDM), angle measuring instrument (Theodolite), and a microprocessor. It can be used to : I. Measure elevations, coordinates, sloping distance, horizontal and vertical angles in tachometric, topographic and geodetic surveys. Measured data can be recorded in the internal memory and transferred to the computer to further process for generating a map of a surveyed area. II. Record excavations by archaeologists.
III. Instantaneously compute elevations, vertical and horizontal distance components, and coordinates, and display on the LCD. IV. Store data either in the internal data storage or the external data collector after measurements are taken. V.
Perform a variety of functions and computations such as :· Averaging multiple angle and distance measurements.· Computing horizontal and vertical distances.· Corrections for temperature, atmospheric pressure, and humidity.· Calculating elevations of points from the vertical distance components.
· Computing polars, inverses, and resections.· Computing X, Y, and Z coordinates. VI. Measure the elevation of objects from far away as figure 3.7.
1, and known as Remote Elevation Measuring (REM).VII. Find the coordinate of missing pillars using two known coordinates as figure 3.7.2.VIII. Find its coordinate using two control points as figure 3.7.
3, and known as resection. IX. Calculate the area of a closed figure using the coordinates of the corner of the figure as figure 3.7.4.