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Ellipsoids and Datums Map projections (3D to 2D)

Lecture 07: Coordinate Transformation I. Overview:. Coordinate system for Earth: Ellipsoids and Datums Map projections (3D to 2D) Planar coordinate transformation (2D to 2D) Geocoding (discrete to continuous). Topics:. Ellipsoids and Datums Map projections (3D to 2D). References:.

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Ellipsoids and Datums Map projections (3D to 2D)

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  1. Lecture 07: Coordinate Transformation I Overview: Coordinate system for Earth: Ellipsoids and Datums Map projections (3D to 2D) Planar coordinate transformation (2D to 2D) Geocoding (discrete to continuous) Topics: Ellipsoids and Datums Map projections (3D to 2D) References: Chapter 3 in Jan Van Sickle’s Basic GIS Coordinates (2004) Chapter 5 in Robinson et al (1995) pp. 61-88

  2. Lecture 06: Digital Terrain Analysis II Outlines 1. Ellipsoids and Datums: A coordinate system for Earth needs Ellipsoid and Datum 1.1 Ellipsoids A shape used to approximation the shape of earth Parameters of a biaxial ellipsoid: (The biaxial ellipsoid figure) Common Ellipsoids: Clarke1866 WGS (world geodetic system) 72 and 84 Airy 1830 - Britain GRS80 – U.S.

  3. 1.2 Datums: 1) A datum is an actual coordinate system: 2) Creation of a datum (definition of a datum): (1) Steps: definition of an ellipsoid (a, b) attaching the ellipsoid to earth Initial point and orientation (five parameters) realization (2) Methods: (a) the old approach definition of an ellipsoid attaching the ellipsoid to Earth through an initial point with an azimuth to another reference point Survey of monuments

  4. 1.2 Datums: (continued…) Drawbacks: regional and nongeocentric (The nongeocentric Ellipsoids Figure) Common datums: NAD27 (Clarke 1866) (b) The new approach Definition of an ellipsoid (Geocentric) Attaching the ellipsoid to Earth Mass center of the earth Three dimensional (The Three Dimensional Figure) GPS positions of monuments Advantage: global, geocentric, 3-dementional (with Z) Common datums: NAD83 (GRS80), NAD83/91 WGS84 (WGS84), WGS84(G730) WGS84(G873)

  5. 1.3 Coordinate transformation between datums 1) Molodenski transformation: (The Molodenski Transformation Figure) 2) Seven-parameter transformation: (three translation, three rotation, one scale) (The Seven-parameter Transformation Figure) 3) Surface fitting: NAD27 to NAD83 (The Surface Fitting Figure)

  6. 2. Map Projection: (3D to 2D) 1) Purpose: 2) Difficulty: Shape of the earth 3) Distortion: Size (Equivalence) v.s. shape (Conformality) 4) Type of projections: (1) The UTM Projection: (The Transverse Mercator Figure) (2) Conformal: angular relationships are maintained (The Lambert Conformal Figure) (3) Equal area: (The Albers’ Equal Area Figure) (4) The State Plane Coordinate System: varies between states.

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