Mapping (Topographic) Surveys

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Mapping (Topographic) Surveys
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Required

• Readings 16-1 to 16-9.1 16-9.5
• Figures 16-1 to 16-4.
• Recommended, not required, extra readings
• Hydrographic Surveys section 16-12.

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Topographic Maps

• Topographic surveys, why?
• Planimetric vs hypsometric maps.
• A combination of Planimetric and hypsometric maps
  is a topographic map.
• DEMs and three dimensional perspective models.

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3-D Representation of a topo mapping of site 1,
project 1
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Methods for Mapping (Topographic) Surveys

• Small areas ground surveys.

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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.
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Large areasLIDAR

• Terrain 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 systems
• Knowing 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 earths 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.

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LIDAR Terrain Mapping in Forests
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Canopy Surface Model
Minus
Terrain Surface Model
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LIDAR Vegetation Height Model (LIDAR Canopy
minus LIDAR Ground DEM)
Canopy Height (m)
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LIDAR data visualization
Click on image
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LIDAR Data Visualization
Click on image

• Raw LIDAR point cloud, Capitol Forest, WA
• LIDAR points colored by orthophotograph
• FUSION visualization software developed for point
  cloud display measurement

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Oblique aerial view, courtesy of Washington Dept.
of Ecology
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Perspective shaded-relief view of 10m DEM,
derived from 124,000-scale contours
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Perspective view of LIDAR DEM
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Interpreted LIDAR DEM. Yellow is landslide, pink
is scarp, green and violet are glacially-scoured
surface
Source http//pugetsoundlidar.ess.washington.edu/
example1.htm
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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.

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Contour Lines

• 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 ft
• Contour intervals depend on map scale and the
  diversity of relief in the area.

• Every fifth contour is drawn
• with a heavier line, elevations
• are in breaks in the contour
• lines.
• Next slide then figure 16-2

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Shaded relief DTM Produced by ArcInfo
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Characteristics of Contours

• Must close on themselves, on or off the map
• Perpendicular to the direction of max. Slope
• Slope between them is assumed uniform
• The distance between them indicates the steepness
  of the slope, gentle or steep
• Irregular signify rough, smooth signify gradual
  slopes

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Characteristics of Contours

• Concentric closed contours hills or depression
• They do not cross each other, only in special
  cases
• They do not cross buildings
• They cross horizontal man made surfaces in
  parallel lines

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Locating Contours

• Direct 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.

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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.

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• 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.

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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 suitable
• for contours.
• GPS
• Must maintain satellite
• Visibility. Will not
• work efficiently
• close to building or
• Under trees.

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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 ft

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Project 2

• Map 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, Radios
• TOB TS on point 36, first point in table is 20,
  must give reference azimuth

point Horiz. Angle reading H. Dsitance Remarks
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X
Contour lines of problem 16-12