Surveying & Measurement Detail Survey Topographic Surveying
Introduction Mapping surveys are made to determine the relief of the earth s surface and locate critical points on it. to determine the locations of natural, and cultural features on the earth s surface, and to define the configuration of that surface.
The Surface Features The features that are included on the map are determined by the purpose of the map. Natural features on the maps include vegetation, rivers, lakes, oceans, etc.
The Surface Features Cultural features on the maps are the products of people, and include roads, railroads, buildings, bridges, canals, boundary lines, etc.
Type of Maps Planimetric; include natural and cultural features in the plan view only, and Topographic; include planimetric features and show the configuration of the earth s surface.
Map Scale The ratio of the length of an object or feature on a map to the true length of the object or feature. Map scales are given in three ways: by ratio or representative fraction, such as 1:2000 or 1/2000 (A scale of 1:2000 means that one unit on the map equals 2000 of the same units on the ground). by an equivalence, for example 1 cm = 200 m. graphically using either a bar scale or labelled grid lines spaced.
Contours A contour is a line connecting points of equal elevations. Contours cannot be seen in nature. On maps, contours represent the planimetric locations of the traces of level surfaces for different elevations. The elevation difference between the adjacent contours is called the contour interval. The contour interval depends on a map s purpose and scale.
Contours (a) Plan view of contour lines (b) Profile view (c) Profile view
Characteristics of Contours Contour lines are continuous. Contour lines are relatively parallel unless one of two conditions exists. A series of V-shape indicates a valley and the V s point to higher elevation. A series U shape indicates a ridge. The U shapes will point to lower elevation. Evenly spaced lines indicate an area of uniform slope.
Characteristics of Contours A series of closed contours with increasing elevation indicates a hill and a series of closed contours with decreasing elevation indicates a depression. Closed contours may be identified with a +, hill, or -, depression. Closed contours may include hachure marks. Hachures are short lines perpendicular to the contour line. They point to lower elevation.
Characteristics of Contours The distance between contour lines indicates the steepness of the slope. The greater the distance between two contours the less the slope. The opposite is also true. Contours are perpendicular to the maximum slope. A different type of line should be used for contours of major elevations. For example at 100, 50 and 10 foot intervals. Common practice is to identify the major elevations lines, or every fifth line, with a bolder, wider, line.
Characteristics of Contours
Characteristics of Contours
Contours are Continuous Some contour lines may close within the map, but others will not. In this case, they will start at a boundary line and end at a boundary line. Contours must either close or extend from boundary to boundary.
Contour Lines are Parallel Two exceptions: They will meet at a vertical cliff They will overlap at a cave or overhang. When contour lines overlap, the lower elevation contour should be dashed for the duration of the overlap.
Valleys and Higher Elevation A series of V-shapes indicates a valley and the V s point to higher elevation.
U Shapes and Ridge A series of U shapes indicates a ridge. The U shapes will point to lower elevation.
Contour Spacing Evenly spaced contours indicate an area of uniform slope. Unevenly spaced contours indicates an area with variable slope.
Hills and Depressions A series of closed contours with increasing elevation indicates a hill. Hills may be identified with a + with the elevations and depressions may be identified with a -.
Hills and Depressions A series of closed contours with decreasing elevation indicates a depression.
Hachures Hachures are short lines which are perpendicular to the contour line. Used to indicate a hill or a depression.
Contour Spacing Contours spaced close together indicate a steep slope. Contours spaced wider apart indicate less slope.
Contours are perpendicular to the maximum slope.
Different types of lines should be used for contours of major elevations. Common practice is to identify the major elevations lines, or every fifth line, with a bolder, wider, line.
Data Acquisition When collecting topo data there are two important issues: Ensuring sufficient data is collected to define the object. Ensuring two types of information is gathered for each station: Location Elevation
Direct Method In this method, the contour lines are physically followed on the ground using a total station. After the instrument set up, the HI is established, and the telescope oriented horizontally. Then for the existing HI, the rod reading (FS) that must be subtracted to give a specific contour elevation is determined. The rod person selects trial points expected to give this minus sight, and is directed uphill or downhill by the instrument operator until the required reading is actually secured.
Direct Method For example: The instrument set up at point A, elevation 674.3 ft, hi 4.9 ft, and HI 679.2 ft. If the 5-ft contours are being located, a reading of 4.2 or 9.2 with the telescope level will place the rod on a contour point. The 9.2-ft rod reading means that point X lies on the 670-ft contour. After the point which gives the required rod reading has been located by trial, the horizontal position of the point is determined by measuring the horizontal distance and direction from the instrument.
Indirect Method No attempt is made to follow the contour lines. Instead a series of spot levels is taken at readily identifiable locations (controlling points) that are critical to the proper definition of the topography such as B, C, D, E, F, and G. Trees, manholes, and intersections of walls and fences are also included. Elevations are determined on these points using total station by employing trigonometric levelling.
Indirect Method Horizontal distance and azimuth are also measured to locate the points. The position of controlling points are then plotted, and contours interpolated between elevations of adjacent points.
Interpolation Drawing contour lines to produce a topographic map requires the ability to interpolated between points. Interpolation is required because contour lines are lines of constant elevation and the station elevations that are measured in the field seldom fall on the desired contour elevation. Interpolating is finding the proportional distance from the grid points to the contour line elevation.
Interpolation Interpolating can be done by estimation for low precision maps. It should be done by calculation and measurement for higher precision maps. A combination of methods can also be used, depending on the use of the map.
Interpolating by Estimation Logic or intuitive reasoning would conclude that when the grid points are at 102 ft elevation and 98 ft elevation, then a contour line of 100 ft elevation would be half way in between. a dashed line has been drawn between the two points. In topographic surveying it is assumed that the area between two measured stations is a plane.
Interpolating by Calculation Proportional distance is calculated using an equation. High elevation - Contour elevation Proporiton = High elevation - Low elevation Example: Determine the location of the 96 foot contour line for the illustration. Dist = HE - CE 99-96 = = 0.75 HE - LE 99-95
Interpolation by Calculation and Measurement Start by selecting an contour interval and two grid points. This example starts with the 110 foot interval. The first step is to calculate the position of the 110 foot contour between stations A1 and A2. % = HE - CE 125-110 = = 0.6 HE - LE 125-100
Interpolation by Calculation and Measurement The next step is to measure and mark the position of 0.6. Next, determine which direction the contour goes between the diagonal and the other three sides of the grid. Mark the next points. P = 0.6 x 1.5 = 0.9
Interpolation by Calculation and Measurement The 110 foot contour line passes between B1 and B2, therefore the next station is the diagonal. These steps are followed one grid line at a time until the contour closes, or reaches the edge of the map. Dist = HE - CE 112 110 = = 1 = 0.167 HE - LE 112 100 0.167 x 2.1 = 0.35
Interpolation by Calculation and Measurement Determining the proportion for line B1:B2. dist = HE - CE 112-110 = = 0.182 HE - LE 112-101 0.182 x 1.5 =.27
Interpolation by Calculation and Measurement The grid lines and diagonals for each square are considered and the contour is extended. Dist = HE - CE 112-110 = = 0.14 HE - LE 112-98 0.14 x 2.1 = 0.294
Interpolation by Calculation and Measurement When the contour points form a closed shape or have extended from one edge of the map to another, a smooth line is drawn connecting the points. The contour lines must be labeled.
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S1
Angle & Distance The first step in producing a topographic map from angle and distance data is drawing a map of the boundaries. To draw the boundaries, the map scale must be selected.
Angle & Distance Drawing Map To determine the map scale the maximum distances must be determined. Study the data table and sketch. The lot is rectangular and the distance from station IP to station D is198.3 ft and from IP to B is 261.2. 198.3 + 261.2 = 459.5 ft. 459.5/50 = 9.19 inches A scale of 1 = 50 will require paper that is 9.19 inches long.
Angle & Distance Drawing Map STA A B C D E F G H I J K L M N O P Q R Dist 267.2 261.2 348.3 198.3 275.1 130.6 65.8 145.7 203.0 266.2 291.3 206.5 65.2 45.3 35.8 148.9 280.3 144.4 0 deg=n Angle 303.5 42.1 126.7 190.3 216.2 358.5 43.3 163.4 195.3 199.7 211.2 214.2 172.0 84.7 291.6 223.3 232.4 295.9 Elev 950.2 961.1 954.9 938.7 933.5 948.3 946.5 940.1 938.8 936.4 932.7 935.2 937.0 940.5 942.0 938.5 937.3 965.5
Angle & Distance Drawing Map North is zero degrees To draw the map the IP is located in the approximate position and the data is used to locate each corner using the angle and the distance. Corner A is 5.3 inches and -56.5o from North and IP. STA DIST ANGLE ELEV A 267.2 303.5 950.2
Angle & Distance Drawing Map Each boundary station is marked on the map using the same method. Station B is 261.2 feet from the instrument position and at an angle of 42.1o. STA DIST ANGLE ELEV B 261.2 42.1 961.1
Angle & Distance Drawing Map Station C is 228.3 feet from the instrument position and at an angle of 126.7. STA DIST ANGLE ELEV C 228.3 126.7 954.9
Angle & Distance Drawing Map Station E is 275.1 feet from the instrument position and at an angle of 216.2. STA DIST ANGLE ELEV E 275.1 216.2 933.5
Angle & Distance Drawing Map This completes the boundary of the lot. The next step is draw the boundary lines.
Angle & Distance Drawing Map The remaining stations are added to the map. Station F is 130.6 feet from the instrument position and at an angle of 358.5o. STA DIST ANGLE ELEV F 130.6 358.5 948.3
Angle & Distance Drawing Map Station G is 65.8 feet from the instrument position and at an angle of 43.3o. STA DIST ANGLE ELEV G 65.8 43.3 946.5
Angle & Distance Drawing Map Station H is 145.7 feet from the instrument position and at an angle of 163.4o. STA DIST ANGLE ELEV H 145.7 163.4 940.1