7 Methods for Mapping (Topographic) Surveys Small areas: ground surveys.33
8 Large areas:-photogrammetry and Remote Sensing, automatic. With ground survey for control, GPS?Overlapped images from a plane, geometry is solved, images are oriented , and finally 3D models are produced and digitized to produce maps.
9 Large areas:LIDARTerrain mapping using scanning airborne laser radar (LIDAR): the aircraft is simply transformed into the equivalent of an airborne total station by combining laser range-finder technology with GPS and inertia systemsKnowing the aircraft position (GPS) and orientation, the distance to the ground point, and the angular orientation of the laser beam, the position of a point on the earth’s surface can be found.Several footprints of laser are available to perform various tasks. For example, large footprints VS small footprints in forested and bare-ground areas.
23 Interpreted LIDAR DEM. Yellow is landslide, pink is scarp, green and violet are glacially-scoured surfaceSource:
24 Control for Topographic Surveys Horizontal: traversing, triangulation, GPS, extended with photogrammetry in large areas.Vertical: leveling loops, GPS.Control points are the framework upon which the topographic details are usually built. Must be:Within the allowable misclosure.Checked and adjusted.46
25 Contour Lines Next slide then figure 16-2 Lines connecting points of equal elevations, such as a shoreline of a lake.Contour Interval: the vertical distance between level surfaces forming the contours. 1, 2, 5 ftContour intervals depend on map scale and the diversity of relief in the area.Every fifth contour is drawnwith a heavier line, elevationsare in breaks in the contourlines.Next slide then figure 16-257
29 Characteristics of Contours Must close on themselves, on or off the mapPerpendicular to the direction of max. SlopeSlope between them is assumed uniformThe distance between them indicates the steepness of the slope, gentle or steepIrregular signify rough, smooth signify gradual slopes68
30 Characteristics of Contours Concentric closed contours: hills or depressionThey do not cross each other, only in special casesThey do not cross buildingsThey cross horizontal man made surfaces in parallel lines68
32 Locating ContoursDirect method: locate the points of certain elevation. Keep a certain rod reading from horizontal line of site, trace and locate points on contour line.Indirect method: measure the elevation and location of “controlling points”. Interpolate to locate contours. Interpolate at each side of controlling features separately.Slide 16-4.79
33 Automated Contouring Systems DTM (DEM): digital elevation (terrain) models.Array of points with measured X, Y, and Z.Grid method: borrow pit, computer interpolation.Irregular method: indirect method, with additional information to produce triangulated irregular network.Assuming the triangle sides are of constant slopes, interpolate along the sides.810
34 Breaklines: linear Topographic features which have uniform slopes. Must be triangle sides.For example: notice how roads are shown in the TIN and in the contours.
35 Field Methods for Locating Topographic Details Radiation by total station: measure angle and distance to each feature. X, Y, Z of the surveyed point can be displayed in real time.Grid method: suitablefor contours.GPS:Must maintain satelliteVisibility. Will notwork efficientlyclose to building orUnder trees.911
36 Accuracy Specifications for Topographic Surveys More than one standards: national map accuracy standards (NMAS), ASPRS, American Society of Civil Engineers (ASCE)Maximum permitted errors are related to map scale. The smaller the scale the bigger the allowed error.Example: not more than 10% of tested points shall be in error in horizontal position by more than 1/30 inch, what about a map 1 in: 100 ft1012
37 Project 2Map the site of project 1, extend it to the edges of vegetation.Map every thing that DOES NOT MOVES, big or small.Use known control stations and coordinate. Keep good sketches.Contours: interpolated from project 1 earthwork grid, extend it to the limits by hand.Check out: TS, battery “check the charge before you leave, tripod, prism or two, prism pole or two, tape measure, RadiosTOB: TS on point 36, first point in table is 20, must give reference azimuthpointHoriz. Angle readingH. DsitanceRemarks