Eo Y. D., Department of Technology Fusion, copyright® Lecture 12. Topographic Surveying

Eo Y. D., Department of Technology Fusion, copyright® General Spatial feature : Relief and shape of surface, natural and man-made features topographic map: Spatial features drawn according to a certain scale and map symbol For topographic mapping, topographic surveys are performed in order to determine the position of natural and man-made features.

Eo Y. D., Department of Technology Fusion, copyright® By using plane table, draft a paper map in the field for topographic mapping. This is detailed surveying using surveying points which are from traverse surveying etc. High precision cannot be obtained, however, it is adequate for complicated geographical features, built-up areas or crop areas since work can be done quickly Advantages –Since paper map is made on the spot, it is possible to draw complicated geographical features. It is also easy to find out errors or misses in surveying –It is unnecessary to read angles or write in field notes. Therefore there is no errors or mistakes caused by it. –Little office work –Work can be done quickly since the structure of equipment is not complicated Disadvantages –Many errors caused by map paper of expansion and contraction –Field work can be time consuming and can be easily affected by the weather –Inconvenient when calculating since there is no field notes, and accuracy is low overall Plane Table Surveying

Eo Y. D., Department of Technology Fusion, copyright® Plane Table setting Leveling –Leveling the plane table –After placing Alidade perpendicular to the tripod and leveling it, rotate it again at its right angle and level it. After this, rotate it at its right angle once more and check for its levelness. Centering –Placing the point marked on plane table and the station on the ground on the same plumb line

Eo Y. D., Department of Technology Fusion, copyright® Plane Table setting Orientation –Fixing the plane table in a certain direction –A method using magnetic needle : Orientation is done by using magnetic meridian of a paper map as its basis. Not accurate –A method using one direction line drawn on a paper map as its basis : Orientated by using the line on the map including centering point. General orientation follows this method and is more accurate then the one using magnetic needle

Eo Y. D., Department of Technology Fusion, copyright® Radial-line method –Surveying traverse or geographic features can be done by setting up a plane table at a station and measuring the distance from the targets around the station to the direction line –Although this is a simple and accurate method, since a number of points should be seen from one station, it is appropriate only for small area, well collimated areas which are within 60m Progression Method –Used for built up areas, roads, and forests where it is not possible to collimate many points from one station, or for surveying long and narrow areas –While observing direction and distance and moving forward from one observation station to another, create traverse on paper map, during this process, collimate pre-observed points and check for errors. This requires a long time since the plane table is moved a number of times. Method of Plane Table Surveying

Eo Y. D., Department of Technology Fusion, copyright® Method of Forward Intersection –Set up plane table at 2 or 3 known stations, collimate unknown positions and draw direction line from these stations. Decide target location with intersection point. –Used when collimating the target is possible but difficult to measure distance due to wide surveying areas and obstacles Method of backward Intersection –Set up plane table at unknown points that are not marked on the paper map and collimate known positions (usually more than 3) and intersect these direction lines. Find out the unknown point on the map by using this intersecting point Method of Side Intersection –A methods using both Forward and Backward Intersection –Decide the direction of unknown point by setting up a plane table at known position then move the plane table back to the unknown point and collimate the unknown point and decide its location Method of Plane Table Surveying

Eo Y. D., Department of Technology Fusion, copyright® Errors and precision Eccentric error –Error (q 1 ) cause by eccentricity, e, since the peephole surface and collimation surface do not coincide (fig.11.8) –q 1 =e/M, M=denominator of scale (1/500 -> M=500) –Generally, e = 25mm, where error tolerance = 0.2mm(drawing error), –e/M < 0.2mm  1/M < 0.2/25=1/125 –That is, eccentric error of surveying in scale of less than 1/125 can be ignored. e a A B D

Eo Y. D., Department of Technology Fusion, copyright® Centering Error –Error caused by imperfect centering –When centering is not perfect, the same error occurs in orientation –q 2 =2e/M –e = 5cm, where error tolerance = 0.2mm(drawing error), –2e/M < 0.2mm  1/M < 0.2/100=1/500 –That is, 5cm Centering error of surveying in scale of less than 1/500 can be ignored. e a A B C B’B’ Errors and precision

Eo Y. D., Department of Technology Fusion, copyright® Error in sighting (normal Alidade) –Collimation error caused by the diameter of the peephole and the thickness of collimation thread –Where the diameter of the peephole d, thickness of collimation thread f, the width of two collimation plate c, the length of direction line(on map) l, the positional error is d/2 B B’B’ c –If d= 0.5mm, f=0.2mm, c=220mm, error tolerance q=0.2mm, l is 163mm –When considering other errors, it is recommended to lower the length of direction line below 10cm in general Errors and precision

Eo Y. D., Department of Technology Fusion, copyright® Precision of Plane Table Surveying –Flat Area : 1/1,000~ –Gentle slope : 1/800~1/600 –Complex and steep slope : 1/500~1/300 Errors and precision

Eo Y. D., Department of Technology Fusion, copyright® A topographic map which serves as the basis of a country National Geographic Information Institute in Ministry of Land, Transport and Maritime Affairs supervises its making National base map such as 1:25,000, 1:50,000, 1:25,000, 1:5,000 are made Recently 1:5,000 digital maps are made Usually made by airborne photogrammetry National Base Map

Eo Y. D., Department of Technology Fusion, copyright® Shading ( 음영법 ) –Relief is marked by the shadow which is formed when parallel light shines in a certain direction from a certain point –Appropriate for features with big relief and sharp inclination Hachures ( 우모선법 ) –Using short and nearly parallel line –Use the distance between lines, thickness, length and direction etc. to mark the ups and downs of a feature –When inclination is steep use thick and short lines, however when inclination is gentle use thin and long lines and mark in the direction of the greatest inclination on the paper Color ( 채색법 ) –Differentiate altitude by coloring the space between contours with the same color –Mark with darker color when the terrain gets higher from the ground –In case of oceans, use darker colors as it get deeper Shading, hachures, and color methods are lack in quantitative expressions and are generally used in small scale maps Representation of topography

Eo Y. D., Department of Technology Fusion, copyright® Spot height ( 점고법 ) –A method of writing numbers at surveying points when indicating water depth in River, harbour, oceanographic surveying –Also used for special terrain such as built-up area Contour lines ( 등고선법 ) –Representing terrain with curved lines which connect points of the same height –The most common way of describing terrain quantitatively Representation of topography

Eo Y. D., Department of Technology Fusion, copyright® DEM(Digital Elevation Model) –Generally represented by regular grid –Each grid point is assigned height value –Ineffective when points of the same height continue TIN(Triangulated Irregular Network ) –Geographical features are represented by a network composed of irregular triangles –Effective representation of geographical features compared to regular grids Representation of topography 3 dimensional model by Computer

Eo Y. D., Department of Technology Fusion, copyright® Types of contour line –Intermediate contour ( 주곡선 ): Main line of contour Line intervals are decided upon scale and precision of map Generally, the contour intervals are M/2,500 (small scale), M/2,000 (large scale) where map scale 1/M –Index contour ( 계곡선 ): For every 5 intermediate contour, thick lines are drawn in order to make the number of intermediate contour easy to see –Half interval contour ( 간곡선 ) : When it is difficult to represent areas with gentle inclination, wavy line is drawn between two intermediate contours –Supplementary contour ( 조곡선 ): Drawn between intermediate contour and half interval contour for precise representation of an area. Less than a quarter of the line interval of intermediate contour Contour

Eo Y. D., Department of Technology Fusion, copyright® Contour type Line type Contour type 1/50,0001/25,0001/10,0001/5,000 4 호 solid line Index100m50m25m 2 호 wavy line Intermediat e 20m10m5m2.5m 2 호 wavy line Half interval 10m5m2.5m1.25m 2 호 dotted line Suppleme ntary contour 주곡선 간격의 1/4 이하 Contour

Eo Y. D., Department of Technology Fusion, copyright® Characteristics of Contour –All points on a single contour have the same height –Must be closed in map or between maps –Center of close : mountain peak or concave area (represented by arrows etc.) –interval between contour lines gentle slope : wide, steep slope : narrow equi-slope area : constant Direction of maximum slope has shortest interval between contour lines Contour

Eo Y. D., Department of Technology Fusion, copyright® Characteristics of Contour –Skip, intersection (cave, cliffs are exceptions →in reality, symbol are used, ramification and coincidence is not applied –Ridgeline, valley, maximum slope lines are perpendicular to contour 고개 Contour

Eo Y. D., Department of Technology Fusion, copyright® 凸線 (ridge) –Connect the highest terrain points 凹線 ( 谷線 ) –Connect the lowest terrain points –Line where rainwater meet Line which change slope –Line when there is an apparent change in the distance between contours –A boundary line where the terrain slope changes –Slope change point =the intersecting point of slope change line and 凹 凸線 –Line with the maximum surface slope –Connect in the direction of the shortest distance among adjacent contours Basic Relief Line

Eo Y. D., Department of Technology Fusion, copyright® Direct Method –Use the principle of leveling to measure the points which are at a certain height and connect these to obtain contour –Appropriate for gentle slope areas which need the precise terrain expression –Use staff and thedolite or tatalstation Contour Measurement

Eo Y. D., Department of Technology Fusion, copyright® Direct Method –Method using staff and theodolite Set up theodolite at known point and adjust collimation horizontally Measure height of instrument and decide on the height of collimation Depending on the spot height desired, decide on graduation of staff which should be identical to collimation Select the point where selected the graduation of staff and collimation are in agreement Determine the direction by measuring the horizontal angle of other known points and surveying point Determine on the distance by Stadia line of theodolite Continue selecting the next point in the same height Contour Measurement

Eo Y. D., Department of Technology Fusion, copyright® Geomatics Engineering (Cho, Yangseogack)

Eo Y. D., Department of Technology Fusion, copyright® Direct method –When using totalstation Input height after installing at known point Collimate other known point and input azimuth Install reflective prism to suit the height of horizontal collimation(instrumental height) Consider instrument as tracking mode and move so it can be of desired height. Save azimuth, horizontal distance and altitude Continue with the next point Contour Measurement

Eo Y. D., Department of Technology Fusion, copyright® Indirect Method –Measuring the horizontal and vertical location of important points such as basic relief line and measure the height using interpolation between adjacent two points (known) –Appropriate for land with high inclination and even ups and downs –There are methods using section/graph method, profiling/cross section surveying method, traverse surveying and radial-line method Contour Measurement

Eo Y. D., Department of Technology Fusion, copyright® Indirect method –Section/Graph method Divide the target area into regular grid with regular intervals and measure the height of intersecting points, put the contour using interpolation between adjacent two points (fig ) Used for rather even areas –Profiling/cross-sectioning survey Mainly used for route surveying such as railroad, road and hydrography Measure the height of each point on the certain centerline (profile) and the height of point (slope changed) on both side-line of center at the same time. Use this data to record contour (fig ) Contour Measurement

Eo Y. D., Department of Technology Fusion, copyright® Geomatics Engineering (Cho, Yangseogack)

Eo Y. D., Department of Technology Fusion, copyright® Geomatics Engineering (Cho, Yangseogack)

Eo Y. D., Department of Technology Fusion, copyright® Indirect method –Method using traverse surveying and radial-line method Measure the main points on a valley or ridge whose inclination and direction change and find the points where contour pass by using interpolation (fig ) Contour Measurement

Eo Y. D., Department of Technology Fusion, copyright® Interpolation –When inclination of two known points (location and height) is equal, the point where contour meets the line made by these two points can be calculated. –That is to say, put the distance between the two known points A,B as D, altitude difference (H B -H A ) as H, the location of a point with H C as its altitude is located D x (H C -H A )/H away from point A Computation of height using contour

Eo Y. D., Department of Technology Fusion, copyright® Cross section mapping using contour Select the section(line AB) which needs to be drawn on cross section of a topographical map (fig ) Mark the intersecting point of cross section base line (line CD) and contour Mark height of intersecting points with contour The scale of cross section does not need to be identical to that of topographic map, generally the vertical scale(height) is greater than lateral scale (horizontal distance)