BT-204 UNIT III MAPPING AND SENSING PDF

# UNIT - III ## MAPPING & SENSING (Contour Lines & Remote Sensing) ## Sushila Devi Bansal College of Technology Umariya, A.B. Road, Indore Page No. 163. **Topic:** Mapping & Sensing **Objective:** To Know about the mapping & sensing & contour lines **Outcomes:** Students will familiarize abou...

# UNIT - III ## MAPPING & SENSING (Contour Lines & Remote Sensing) ## Sushila Devi Bansal College of Technology Umariya, A.B. Road, Indore Page No. 163. **Topic:** Mapping & Sensing **Objective:** To Know about the mapping & sensing & contour lines **Outcomes:** Students will familiarize about the contour line & remote sensing. ## UNIT-3 [Mapping & Sensing] **RP-243** ### Introduction The relative positions of points in a plan are represented by a map. The importance of the map is considerably increased if along with the horizontal positions of the features, their relative heights are also represented. Such maps are known as topographical maps. A topographical map presents a clear picture of the surface of the ground. It shows various ground features like river, ponds, valleys, slopes, depressions, roads, railways, vegetation, etc. The features of the ground are generally shown by symbolic notations. In topographical survey, both horizontal as well as vertical controls are exercised. A topographical map shows horizontal & vertical details simultaneously. The relative heights of various points can be represented by various methods such as shading, Form lines, hachures, contour lines, etc. Out of them contour lines being the best method of representing the elevations of the points, in the plan. Contour lines are quite helpful to make topographical maps more expressive and comprehensive. ### Topographical Map Topographical maps are nothing but contour maps on which various features existing on the ground surface are relatively shown. ### Contour Lines A contour line is an imaginary line formed by joining the points of the same. It is a line in which the surface of the ground is intersected by a level surface. This is the best method of representation of features such as hills, depressions, undulations. ### Contour Interval The vertical distance between any two consecutive contours is called Contour Interval. The contour interval is kept constant for a contour plan, otherwise the general appearance of the map will be misleading. The choice of proper contour interval depends upon the following considerations. 1. **The Nature of The Ground:** For undulating and rough hilly ground, the contour interval should be more. In such cases, if very small contour interval is adopted, the contours will come too close to each other. Smaller contour intervals should be adopted for comparatively flat ground. 2. **The Scale of The Map:** The Contour interval should be inversely proportional to the scale of the map. If the scale is small, the contour interval should be large. If the scale is large, the contour interval should be small. 3. **Horizontal Equivalent:** The horizontal distance between two consecutive contours is termed as horizontal equivalent. It is not a constant value. It varies from point to point depending upon the steepness of the ground. Steeper the ground, lesser in the horizontal equivalent. 4. **Contour Gradient:** A line lying on the ground surface throughout, and maintaining a constant inclination to the horizontal is termed as contour gradient. It can be located by means of a clinometer, theodolite or a gradienter. It is generally used for road & railway routes in hilly areas. 5. **Contour Map:** It is the map of the ground surface which gives the elevations of different points of the ground surface. ### Uses of Contour Maps Following are the various uses of the contour maps: 1. The nature of the ground surface can be understood. A suitable alignment can be selected for engineering projects e.g. Roads, Railways, Irrigation Canals etc. 2. The capacity of reservoir can be approximately computed. 3. The area of catchment can be computed. 4. The intervisibility of different points can be estimated. 5. The quantity of earthwork can be computed. 6. Suitable sites can be selected for construction activities. ### Characteristics of Contours 1. Two contours of different elevations do not cross each other except in the case of an overhanging cliff (steep rock face at the edge of the cliff). 2. Contours of different elevations, do not unite to form one contour, except in the case of a vertical cliff. 3. Contours drawn closer depict a steep slope and if drawn far apart it represents a gentle slope. 4. Contour lines cross valley lines or ridge lines at right angles. ### Methods of Contouring There are two methods of contouring: 1. **Direct Method:** Contours can be drawn with the help of horizontal & vertical measurements of the different points located on the ground. In this method, the reduced level of various points are located. The contours are then drawn by joining these points. Horizontal measurements are made with the help of chain or tape, and vertical positions are found out by level or theodolite. 2. **Indirect Method:** There are various indirect methods of contouring, which are as follows: a. **Method of Squares:** In this method, the area is divided into squares forming a grid. The reduced levels of the corners are determined. The contours of different elevations are then interpolated. This method is suitable for a small open area. b. **Method of Cross Sections:** In this method, a traverse is run and cross sections are projected from this traverse line. The levels are taken at points of these cross sections. The contours are then interpolated. This method is suitable for Railways, Roads etc. c. **Tacheometric Methods:** Entire area is first covered by a network of traverse stations. From the traverse station radial lines are drawn at some angular interval and a tacheometer is placed on these radial stations. Observations are made on all these radial stations, and the elevations and distances are calculated, and from the observations taken, then contours are interpolated. ### Computations of Areas The methods of determining the areas may be classified as: 1). **Calculation of areas based upon field measurements.** 2). **Measurement of regular plan area by Planimeter.** ### Calculation of Areas based upon field measurements There are three methods: 1. **By dividing the area into a number of triangles.** 2. **By dividing the plan area into squares of regular sizes.** 3. **By offsets from the base line:** * **Area of triangle:** $S(S - a)(S - b)(S - c)$ * $a$, $b$, $c$ = lengths of the sides of the triangle. * $S$= half the perimeter of the triangle. * $S = \frac{a + b + c}{2}$. If base (b) & height (h) of the triangle are known, then its area can be determined by using the following formula: Area of triangle = $\frac{1}{2} \times b \times h$. ### By offsets from the base line The following are the mid ordinates which can be used for this purpose: a. **Ordinate Rule** b. **Average ordinate Rule** c. **Trapezoidal Rule** d. **Simpson’s Rule** * **Area:** $\frac{1}{n}(h_{1}+h_{2}+h_{3}+...+h_{n}) \times L$ * **Area:** $(h_{1}+h_{2}+h_{3}+...+h_{n}) \times d$ * **Area:** $d\times \sum_{i=1}^{n} h_i$ * $d$ = common interval * $n$ = number of divisions * $L$= Total length of the line ### Average ordinate Rule * **Area:** $\frac{Sum of ordinates \times length of base line}{No. of ordinates}$ * **Area:** $(\frac{O_{1}+O_{2}+O_{3}+...+O_{n}}{n +1}) \times L$ * **Area:** $\frac{\sum_{i=1}^{n} O_i}{n+1}$ * $O_{1}$ = the ordinate at one end of the base line. * $O_{n}$ = the ordinate at other end of the base line. * $n$ = number of divisions. * $O_{2}$ $O_{3}$....$O_{n}$ = ordinates at the ends of each division. ### Trapezoidal Rule * **Area =** $\frac{Common interval}{2} (1^{st} ordinate + last ordinate) + 2(Sum of the rest of ordinates)$ * **Area =** $\frac{d}{2} ( O_{1} + O_{n}) + 2( O_{2} + O_{3} + ... + O_{n-1})$ ### Simpson’s rule: * **Area =** $\frac{Common interval}{3} (1^{st}ordinate + last ordinate) + 4 (Sum of even ordinates) + 2 (Sum of odd ordinates)$. * **Area=** $\frac{d}{3} (O_{1} + O_{n}) + 4 (O_{2} + O_{4} + ... ) + 2 (O_{3} + O_{5} + ...) $ Simpson’s rule is more accurate. ### Formula for calculation of volumes  where: * $D$= Common distance between sections. * $A_{1}, A_{2},...A_{n}$ = area of cls. * $n$ = Number of cls. ### Trapezoidal Formula * **Area =** $\frac{D}{2} (A_{1}+A_{n}) + 2 (A_{2} + A_{3} + ... + A_{n-1})$. * **Vol =** $\frac {Common distance}{2} \times{ (Area of 1^{st} sector + area of last sector) + 2 (Sum of areas of rest sectors)}$. ### Prismoidal Formula * **Area =** $\frac{D}{3} (A_{1}+A_{n}) + 4 (A_{2} + A_{4} + ...+ A_{n-1}) + 2 (A_{3} + A_{5} +...+ A_{n-2})$. * **Vol =** $\frac{Common distance}{3} \times { (Area of 1^{st} sector + area of last sector) + 4 (Sum of areas of even sectors) + 2 (Sum of areas of odd sectors)}$. ## Sushila Devi Bansal College of Technology Umariya, A.B. Road, Indore Page No. P-172 ## Remote Sensing Remote sensing is broadly defined as collecting & interpreting information about a target object from a distance. It is the method used to study the physical & chemical characteristics of objects from a distance. Aircraft, Satellites, and commonly, cameras, scanenrs, radar sets & sensors, are used for remote sensing. Collection of data is usually carried out by high sophisticated sensors. e.g Cameras, Scanners, radarsets. ## Application of Remote Sensing 1. **Environmental application:** Remote sensing is a vital source of environment information. It is the best means of collecting aspects of weather, pollution, weather forecasting, many basic information for ozone layer depletion & global warming. It is useful for reconnaissance & detailed exploration. 2. **Mineral Exploration:** Remote sensing techniques and reconnaissance & detailed exploration of minerals, fossil fuels. It has proved useful for locating boundaries of mines, mapping local fracture patterns, detecting rocks associated with ore deposits, providing basic geological information, etc. 3. **Land use & Land cover patterns** 4. **Natural Hazards** 5. **Archeology:** Remote sensing has found a widespread use in archeology. Remote sensor images are able to recognize prehistoric archeological patterns & buried archaeologically important sites. ## Summary * Introduction of mapping & sensing. * Contour lines & uses of contours. * Methods of Contouring. * Computations of areas & volas. * Remote sensing & its applications. ## Sushila Devi Bansal College of Technology A.B. Road, Indore ## Assignment / Tutotial - 3 **Important Quests** Basic Civil Engg & Engg. Mech (BT-2-04) **Q1.** What do you understand by term **Contour**? Explain various characteristics of **contour** **Q2.** What is **remote sensing** & its application. **Q3.** Discuss various methods used for calculation of area. **Q4.** The following offsets were taken from a chain line to hedge. | Distance (m) | 0 | 20 | 40 | 60 | 80 | 100 | 160 | 220 | 280 | |---|---|---|---|---|---|---|---|---|---| | Offset (m) | 9.4 | 10.8 | 13.6 | 11.2 | 9.6 | 8.4 | 7.5 | 6.3 | 4.6 | **Compute the area included by the chain line & the offset by** (i) **Mid - ordinate rule.** (ii) **Simpson’s rule** (iii) **Trapezoidal rule.** **Q5.** Define the following term related to contour. 1. **Contour** 2. **Horizontal Equivalent.** 3. **Cliff** 4. **Contour interval** 5. **Grade contour** 6. **Ghat tracer** 7. **Ridge line** 8. **Valley line**