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Technology 3 Holden 0

Technology 3 Holden 0. L3 –Data Models Ch. 2, pp 54-End. 1. Object Data Models. The object data model has many similarities to object-oriented programming. It encapsulates information and operations into discrete objects. Smallworld.

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Technology 3 Holden 0

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  1. Technology 3Holden 0 Lecture 3

  2. L3 –Data ModelsCh. 2, pp 54-End Lecture 3 1

  3. Object Data Models • The object data model has many similarities to object-oriented programming. • It encapsulates information and operations into discrete objects. Lecture 3

  4. Lecture 3

  5. Smallworld • Smallworld GIS is one of the leading geopgraphical information systems (GIS) designed for the management of complex utility or telecommunications networks. • It uses an object-oriented programming language called Magik. Lecture 3

  6. Advantages and Disadvantages • Discrete features are more amenable than continuous to the object-oriented approach. • Object definition and indexing can be complex. • There is a steeper learning curve for developers. Lecture 3

  7. Raster Files and Data Compression • Compreseeion is most often applied to discrete raster data. • Lossy vs lossless compression • Common compression formats: • Run length encoding • Block encoding • Chain encoding • Quad trees Lecture 3

  8. Figure 3.11 Feature coding of cells in the raster world Lecture 3

  9. Raster data compaction techniques Lecture 3

  10. Raster data compaction techniques Lecture 3

  11. Raster data compaction techniques Lecture 3

  12. Figure 3.13 The quadtree Lecture 3

  13. Raster Formats • Single band - shades of grey • Multi-band • Used primarily for images • Generally 3 bands • Red • Green • Blue Lecture 3

  14. Raster Pyramids • Pyramids are the same file stored at varying resolutions. • It speeds up the display, but there are other more efficient ways of doing this. • It comes at a cost in both size and complexity of the data set. • In ArcGIS when asked if you wish to create pyramids, the answer should be yes. Lecture 3

  15. Geodesy, Datums, Projections and Coordinate Systems Chapter 3 Lecture 3

  16. Defining a Spatial Referencing System • Every spatial feature needs to be referenced to a location for GIS use • Spatial reference systems provide a framework to define positions on the Earth‘s surface. • Steps • Define the size and shape of the Earth. • Establish a datum – reference surface from which other points can be measured. • Develop a spatial reference system: • Origin • Orientation of the axes • Units of measure Lecture 3

  17. The Earth is NOT an Ellipsoid (only very close in shape) The Earth has irregularities in it - deviations from a perfectly ellipsoidal shape These deviations are due to differences in the gravitational pull of the Earth Deviations are NOT the surface topography Lecture 3

  18. The Earth’s True Shape is Best Described as a GEOID Lecture 3

  19. The Geoid is a measured surface (not mathematically defined) Found via surface instruments (gravimeters) towed behind boats, planes, or carried in vehicles. Or, from measurements of satellite paths (ephemerides) May be thought of as an approximation of mean sea level Lecture 3

  20. Local or Regional Ellipsoid Origin, r1, and r2 of ellipsoid specified such that separation between ellipsoid and Geoid is small These ellipsoids have names, e.g., Clarke 1880, or Bessel Lecture 3

  21. Global Ellipsoid Selected so that these have the best fit “globally”, to sets of measurements taken across the globe. Generally have less appealing names, e.g. WGS84, or ITRF 2000 Lecture 3

  22. Lecture 3

  23. Cartesian Coordinates (axes are at right angles) Generally, location is defined in two dimensions, X and Y, or in three dimensions, the X, Y, and Z Two-dimensional system most often used with Projected coordinates Three dimensional system used with Geocentric coordinates 90o y Origin 0,0 x z 0,0,0 x y Lecture 3

  24. Spherical Coordinates Use angles of rotation to define a directional vector Use the length of a vector originating near the ellipsoid center to define the location on the surface Lecture 3

  25. Greenwich Observatory The lat/long lines form the graticule. The Parallels The Meridians Lecture 3

  26. Defining a Datum Horizontal Datum Specify the ellipsoid Specify the coordinate locations of features on this ellipsoidal surface Vertical Datum Specify the ellipsoid Specify the Geoid – which set of measurements will you use, or which model Lecture 3

  27. There are two horizontal control networks commonly referred to North American Datum of 1927 (also NAD27) North American Datum of 1983 (also NAD83), to replace NAD27 Lecture 3

  28. NAD27 vs NAD83 Kansas Lecture 3

  29. Datum “Adjustment” A datum adjustment is a calculation of the coordinates of each benchmark – this is how we specify the “reference surface” Not straightforward, because of contradictions Errors in distance, angle measurements Improvements in our measurements of Geoid, best spheroid Improvements in computing capabilities Lecture 3

  30. Vertical Datums Like horizontal, but referenced to standard elevation and established using vertical leveling  Two major vertical datums,  North American Vertical Datum of 1927 (NAVD29), and an update,  North American Vertical Datum of 1988 (NAVD88) Lecture 3

  31. Map projections are used to transfer or “project” geographical coordinates onto a flat surface. . There are many projections: Maine example: • NAD 27 Universal Transverse Mercator – Zone 19N • NAD 27 Maine State Plane • East Zone • West Zone • NAD 83 Universal Transverse Mercator– Zone 19N • NAD 83 Maine State Plane • East Zone • Central Zone • West Zone Lecture 3

  32. Many Projections: Minnesota example http://rocky.dot.state.mn.us/geod/projections.htm Lecture 3

  33. Projections may be categorized by: • The location of projection source • The projection surface • Surface orientation • Distortion properties Lecture 3

  34. Categorized by the Location of Projection Source Gnomonic - center of globe Stereographic - at the antipode Orthographic - at infinity Lecture 3 Source:http://www.fes.uwaterloo.ca/crs/geog165/mapproj.htm

  35. The projection surface: Cone – Conic Cylinder - Cylindrical Plane - Azimuthul Lecture 3

  36. Projection Surfaces – “developable” Lecture 3

  37. The Tangent Case vs. The Secant Case In the tangent case the cone, cylinder or plane just touches the Earth along a single line or at a point. • In the secant case, the cone, or cylinder intersects or cuts through the Earth as two circles. • Whether tangent or secant, the location of this contact is important because it defines the line or point of least distortion on the map projection. • This line of true scale is called the standard parallel or standard line. Lecture 3

  38. The Orientation of the Surface Lecture 3

  39. Projections Categorized by Orientation: • Equatorial - intersecting equator • Transverse - at right angle to equator Lecture 3

  40. Specifying Projections • The type of developable surface (e.g., cone) • The size/shape of the Earth (ellipsoid, datum), and size of the surface • Where the surface intersects the ellipsoid • The location of the map projection origin on the surface, and the coordinate system units Lecture 3

  41. Defining a Projection – LCC(Lambert Conformal Conic) • The LCC requires we specify an upper and lower parallel • An ellipsoid • A central meridian • A projection origin origin central meridian Lecture 3

  42. Conformal Projections • Locally preserves angles/shape. • Any two lines on the map follow the same angles as the corresponding original lines on the Earth. • Projected graticule lines always cross at right angles. • Area, distance and azimuths change. Lecture 3

  43. Equidistant Projections • A map is equidistant when the distances between points differs from the distances on Earth by the same scale factor. Lecture 3

  44. Equivalent Projection • Equivalent/equal area projections maintain map areas proportional to the same areas of the Earth. • Shape and scale distortions increase near points 90o from the central line. Lecture 3

  45. “Standard” Projections • Governments (and other organizations) define “standard” projections to use • Projections preserve specific geometric properties, over a limited area • Imposes uniformity, facilitates data exchange, provides quality control, establishes limits on geometric distortion. Lecture 3

  46. National Projections Lecture 3

  47. Lecture 3

  48. Map Projections vs. Datum Transformations • A map projections is a systematic rendering from 3-D to 2-D • Datum transformations are from one datum to another, 3-D to 3-D or 2-D to 2-D • Changing from one projection to another may require both. Lecture 3

  49. From one Projection to Another Lecture 3

  50. Lecture 3

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