Expressing Position: Coordinate Systems

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Expressing PositionCoordinate Systems

• ERE 371

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Introduction

• Need system to express location
• Issues
• Coordinate approaches

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Geographic Coordinates

• AKA geodetic coordinates
• Components

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Geographic Coordinates
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Geocentric Cartesian Coordinates

• 3-D system
• Orthogonal X, Y, Z axes
• Origin at geocenter
• Orientation of axes based on

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Geocentric Cartesian Coordinates
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Plane Coordinates

• Challenge
• Most surveys ignore curved earth
• Considerations

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Map Projections

• Aim of map projections
• Application
• Example coordinate systems

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Projection Concepts

• Transfer earth location to plane
• Challenge with map projection

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Developable Surfaces
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Projection Distortion

• Challenge
• Distortions are acceptable
• Limiting distortion

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Transverse Mercator Projection

• Use fictitious cylinder
• Scale
• Applications

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Transverse Mercator Projection
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Transverse Mercator Projection Scale Variation
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Transverse Mercator Projection Scale Variation
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Lambert Conformal Conic Projection

• Use fictitious cone
• Scale
• Application

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Lambert Conformal Conic Projection
Standard parallels (line of equal scale)
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Lambert Conformal Conic Scale Variation
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Lambert Conformal Conic Scale Variation
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Geodetic and Grid Azimuths

• On projection
• Implication
• Difference between grid vs. geodetic azimuth
  varies
• Size of difference related to

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Geodetic and Grid Azimuths
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State Plane Coordinate Systems

• National Geodetic Survey (NGS) designed plane
  coordinate system for each state
• Use transverse Mercator or Lambert projection
• Scale distortions limited to 110,000 if
• Width of zones is less than 158 miles
• 2/3 of zone between lines of zero scale change
• Break large states into zones to limit scale
  distortion
• NY has four zones uses both projections
• Alaska and Florida use both projections

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UTM Coordinate System

• U.S. military designed global plane coordinate
  system
• Application

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UTM Zones Over New York State
Zone 18
Zone 19
Zone 17
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Coordinate Systems and Datums

• Issue
• Horizontal datums
• Large area datums ellipsoidal reference
• Examples NAD27, NAD83, WGS84
• Challenges
• Coordinate systems may use specific datum
• SPCS27 State plane coordinates using NAD27
• SPCS83 State plane coordinates using NAD83
• Fundamental theory same parameters vary

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Readings

• Chapter 20 sections 20.1 20.5, 20.12 20.13