CHAPTER 10. Digital Mapping and Earthwork

Transcription

1 CHAPTER 10 Digital Mapping and Earthwork CE 316 March

2 10.1 Introduction 349

3 10.2 Single Images Rectified Photograph With a single photograph, X,Y data can be extracted after the photo has been rectified. If this tilt can be eliminated, a rectified image, which is essentially a map, is the result.. H f Vertical Photo Where f is the camera s focal length Tilted Photo AB and DE are equal distances apart D E 350

4 10.3 Stereomodel scaled replica of a terrain that has been photographed from two or more points of view so that the resulting image can be viewed in 3D. Each photo has 6 degrees of freedom, position and rotation along the X, Y, and Z axis. These 12 elements are recovered with the orientation. Interior orientation. Accomplished by the proper placement of the film in the projector. Relative orientation, where the stereomodel is established at an unknown scale. The two projections are aligned relative to each other using ground points that appear on both images. This fixes 5 of the elements of one of the pictures (all but the distance the projectors are apart. 351

5 Digital Elevation Maps Surface terrain is represented as a network of points of known X, Y, and Z coordinates Stereomodel These are created by digitizing a rectified image, and using a series of known control points to find the absolute coordinates of points on the DEM. 352

6 10.3 Stereomodel Orthophotography 353

7 10.4 Contours and Contour Lines contours: a line of constant elevation on the ground surface. Triangulated Irregular Network (TIN): Uses a DTM to create a view of the terrain. Computer generated contours Triangulated irregular network (TIN) Hachures 354

8 10.4 Contours and Contour Lines Digital Elevation Map: example 355

9 10.4 Contours and Contour Lines Digital Elevation Map: example 2 356

10 10.4 Contours and Contour Lines Topographic Map Construction Project Specifications. Accuracy contents of map Aerial Cameras Specially designed precise equipment Photo Control Survey Ground control is a link between photos and the earth s surface Aerial Photography must be done on a clear day 2D information can be obtained by 1 photo Overlapping photos are needed to extract 3D information standard overlap is 60%, 80% for orthophotos 357

11 10.4 Contours and Contour Lines Topographic Map Construction Analytical Aerotriangulation position of control points are measured with this information, the position and orientation of each camera when the picture was taken, can be found. After this, the ground coordinates of any point can be computed Stereo Data Capture Stereoplotters allow the user to view the photo in 3D and to input the X,Y, and Z points into the computer. Planimetric data: feartures such as buildings, roads, rivers, etc. Topographic data: breaklines, profiles, etc. Product Generation processing digital data into a useful product planimetric map overlayed on an orthophoto TIN 358

12 10.4 Contours and Contour Lines Topographic Map Construction Example: Mount Washington Placement of ground control points 359

13 10.4 Contours and Contour Lines Sample GPS Data Station ID: 3029 Session #: Feb 11, :28 Reference Position - NOT SPECIFIED: Lat. = 0:00'00.000" N Long.= 0:00'00.000" W Height = 0.0 [meters] Antenna height = [meters] (entered in the field in meters Receiver serial # = Antenna serial # = (entered in the office) NP Software = 2.50 SP Software = 0.11 Download Software = Survey schedule: UNSPECIFIED Data-logging start time = 17:44 Data-logging stop time = 22:02 SV Selection mode = AUTOMATIC Elevation mask = 15 [degrees] Minimum # of SVs = 4 Survey sync rate = 15.0 [sec] 3D Position Best PDOP Position [ 1.8] Mean Position [15430] Latitude: 49:46' " N 49:46' " N Longitude: 125:17' " W 125:17' " W Height [m]: D Position Position not available 360

14 10.4 Contours and Contour Lines 361

15 10.4 Contours and Contour Lines 362

16 10.4 Contours and Contour Lines 363

17 10.4 Contours and Contour Lines Planimetric map overlayed on an orthophoto of Mt Washington 364

18 10.4 Contours and Contour Lines Topographic map of area 365

19 10.4 Contours and Contour Lines Selected Cross Section 366

20 10.4 Contours and Contour Lines 367

21 Elevation (m) 10.4 Contours and Contour Lines Example at the Lanigan Mine The Slurry wall centerline was surveyed twice, first using the Mine s datum which was tied into a bench mark in The second survey was tied into another benchmark near the mine in the summer of The two elevations differed as shown in the graph below CL Slurry Wall Centerline Elevations 0+900CL 1+100CL 1+300CL 1+500CL 1+700CL Atlis Datum Mine Datum Station 368

22 10.5 Construction Survey Surveying on a construction site is used to: establish a system of markers in plan and elevation from which measurement of earthwork and structures can be taken making measurements necessary to verify the location of existing construction and to determine the volume of work preformed. 369

23 10.5 Construction Survey Placement of Slope Stakes By method of slope distance A sighting is taken at A where AB equals the instrument height 370

24 10.5 Construction Survey Placement of Slope Stakes The difference in elevation between point A and D is V = I sin a The distance between the points is: D = I cos a d(calc) = w/2 + s(c +/- V) or w/2 + s(f +/- V) where: (c + V) is used for an uphill sight (c - V) is used for a downhill sight c is the cut at the centerline f is the fill at the centerline When the calculated value of d equals the d obtained by field measurements, the correct position for slope stakes has been found. 371

25 10.5 Construction Survey Cut and Fill Volumes BY END AREAS Where:A1 and A2 are the end areas Error in this formula is usually insignificant in comparison to the volume of earthwork. 372

26 10.5 Construction Survey Cut and Fill Volumes BY PRISMOIDAL FORMULA A1 4Am A2 V L 6 Where A m is the area of the section midway between A 1 and A 2 This formula can be used if more precise values are needed. 373