Reference Systems (Projections, Datums, Coordinates) and Surveys

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Reference Systems (Projections, Datums,
Coordinates) and Surveys
Source Peter H. Dana, The Geographer's Craft
Project, Department of Geography, The University
of Colorado at Boulder, http//www.ncgia.ucsb.edu/
education/curricula/giscc used with permission
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Projections

• Worlds not flat (despite what you have heard
  from Dr. K!)
• We want to tie our plane surveys to global
  systems
• Submeter accuracy
• GPS
• Satellite imagery

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Projections

• Conformality
• Distance
• Direction
• Scale
• Area

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Mercatur
Lambert
Lat-Long (unprojected)
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Scale true on 2 parallels
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Secant at 45 (minimizes shape distortion)
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Note shift of latitude lines(minimizes area
exaggeration)
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Constant azimuth for lines
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Preserve distance along great circle
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Pseudocylindrical
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North American Projections
Equal Area Equal Dist.
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Iowa State Plane USGS topos
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Similar to Gall, no secant
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State Systems (hybrids)

• Origin
• 3110 North
• 10000 West
• standard parallels
• 2725 North
• 3455 North

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Iowa DOT Lambert Hybrid
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Datums

• Define the shape of the earth
• Range from flat-earth to complex
• Wrong datum may produce 100s of meters in error
• cartography, surveying, navigation, and
  astronomy, geodesy

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Geometric Earth Models

• Early ideas of the figure of the earth resulted
  in descriptions of the earth as an oyster (The
  Babylonians before 3000 B.C.), a rectangular box,
  a circular disk, a cylindrical column, a
  spherical ball, and a very round pear (Columbus
  in the last years of his life).

You are here!
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Geometric Earth Models

• Flat earth models are still used for plane
  surveying, over distances short enough so that
  earth curvature is insignificant (less than 10
  kms).

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• Looks like a sphere, but flat here, and here

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The best ellipsoidal models can represent the
shape of the earth over the smoothed, averaged
sea-surface to within about one-hundred meters.
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• Sea level average surface of the oceans ( is far
  more complex)
• Tidal forces and gravity cause surface to vary by
  hundreds of meters!
• Gravity models and geoids are used to represent
  local variations in gravity that change the local
  definition of a level surface

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Geodetic Height
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Coordinate Systems

• Based on
• Datums
• Units
• Projections
• Reference systems

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UTM

• Note false easting
• False northing in southern hemisphere

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Local Adjustments

• May need a scaling factor to make total station
  measurements match regional coordinate systems
• e.g., Iowa DOT develops a scaling factor for each
  project
• Based on an accurately measured point in the
  center of the project
• Not using a scaling factor can produce a 12
  error 30 miles from project center

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Public Land Rectangular Surveys (USPLS)

• Townships, square with six miles on each side,
  are numbered with reference to a baseline and
  principal meridian.
• actually, few townships are truly square due to
  convergence of the meridians.
• Ranges are the distances and directions from
  baseline and meridian expressed in numbers of
  townships.
• Every four townships, a new baseline is
  established so that orthogonal meridians can
  remain north oriented.

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• Metes and Bounds
• Metes and Bounds identify the boundaries of land
  parcels by describing lengths and directions of a
  sequence of lines forming the property boundary.

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Linear Referencing Systems

• Methods
• Milepost
• Milepoint
• Cogo (project coordinates)
• Lat-Long
• Projected coordinates
• Address
• Literal description

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Linear Referencing Systems

• CAD/cartography
• Linear Datum
• Anchor points
• Anchor sections
• Reference points

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DOT Hwy Surveys

• The use of photogrammetry, CAD, GPS to establish
  design controls and details
• Survey methods
• Ground survey windshield, transit, level, rod,
  chain, EDM, total station
• GPS, DGPS, Kinematic GPS - smaller crew needed
• Photogrammetry (with control points established
  by a or b above), including digital photography,
  orthos, softcopy
• LIDAR (Light Detection and Ranging)

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Survey Types

1. Desk Study
2. Reconnaissance/cornerstone survey (used to
   validate or even provide a base map of culture
   and topography sufficient to select prelim.
   aligns.) width usu. 0.4 0.6 of total length of
   project, 1100 or 200, 2-5 contours
3. Location or Preliminary (identify BOP, EOP, and
   PIs, and key features (drainage, environmental
   land, archeological/cultural, traffic)
4. Final or Construction survey centerline by
   station, slope stakes, drainage, edge of
   pavement, offset, permanent land corners,
   right-of-way markers

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Wright, Paul, Highway Engineering, 6th Ed. Wiley,
1996