Changes between Initial Version and Version 1 of Ivor's_Geo_Talk_Slides


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Timestamp:
Nov 19, 2005, 10:51:07 AM (16 years ago)
Author:
Dominic Hargreaves
Comment:

Imort from old wiki

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  • Ivor's_Geo_Talk_Slides

    v1 v1  
     1Originals at http://un.earth.li/~ivorw/slides/geogmod.ppt - turned into PDF by Dom and transcribed by me.
     2
     3=== Geographical perl modules ===
     4
     5 * Some etymology
     6   * geo'graphy - Drawing the Earth
     7   * geo'metry - Measuring the Earth
     8
     9 * The interest in geography
     10   * The Open Guide to London
     11   * Geocache, MUD-London and other web based mapping ideas
     12   * 'Grubstreet' had map links with OS grid coordinates (www.streetmap.co.uk)
     13   * We can use the X and Y to plot a map.
     14   * [map with grid and icons of beer, knife and fork, tube sign]
     15 * Find by distance
     16   * We know the location of A (X1, Y1)
     17   * We know the location of B (X2, Y2)
     18   * The distance between them is Sqrt( (X2-X1)^2 + (Y2-Y1)^2 )
     19   * And: OS eastings and northings work in metres
     20 * BUT: everyone else uses Latitude and Longitude
     21   * The standard for GPS
     22   * Works worldwide
     23 * The problem
     24   * The world is <strike>flat</strike>round
     25 * Latitude and Longitude are angles
     26 * Mercator's projection
     27   * Was designed for nautical use
     28   * Preserves angles (azimuth, heading)
     29   * Distorts large distances
     30   * Works well over short range distances
     31   * The Mercator projection is geared to temperate latitudes (eg Europe)
     32 * Transverse Mercator
     33 * Ordnance Survey Grid
     34   * Is a transverse Mercator, with false (offset) Easting and Northing
     35   * A perl module exists to convert between OS Grid and Lat/Long - Geography::NationalGrid
     36 * Geography::NationalGrid
     37   * Object Oriented interface
     38   * Each object is a location
     39   * As parameters to new specify one of the following: Lat/Long; OS Grid reference e.g. TQ 123456; 6 digit Easting and Northing (ie X and Y)
     40   * Method calls include: latitude, longitude, gridReference, easting, northing, deg2string( $degrees) (converts an angle to degrees, minutes and seconds)
     41   * Subclassable
     42   * Subclasses are used to implement grids for individual countries
     43   * The module comes with Geography::NationalGrid::GB and Geography::NationalGrid:: IE
     44 * Back to OpenGuides
     45   * Location and find_by_distance are based on the Ordnance Survey grid
     46   * The Ordnance Survey charge $$$ licence fees to use their data and maps
     47   * We want a system that will work outside the UK and Ireland
     48 * Why don't we do it ourselves?
     49   * Radius of a circle of parallel is R = EcosA where E = radius of Earth, A = latitude
     50 * The radian approximation
     51   * For small theta, sin theta < theta < tan theta (theta must be in radians)
     52   * For a small distance on the ground the conversion between lat/long and X/Y is linear
     53 * Transverse Mercator revisited
     54   * There is an emerging standard , UTM - Universal Transverse Mercator
     55   * It is not UK-centric
     56 * Problem #2
     57   * The earth is <strike>flat</strike> <strike>round</strike> squashed
     58 * The earth is an oblate spheroid
     59   * More like the shape of an apple than a ball
     60   * Instead of projecting onto a cylinder we project onto an ellipsoid
     61 * To use UTM
     62   * You need to specify a datum. This includes an ellipsoid and offsets (false easting and false northing)
     63 * Geo::Coordinates::UTM
     64   * Takes an ellipsoid, not a datum. Hence no internal facility for false easting and northing.
     65   * Non OO interface
     66 * latlon_to_utm
     67   * my ($zone, $east, $north) = latlon_to_utm( 'clarke 1866', 98.251, 2.562 );
     68 * utm_to_latlon
     69   * my ($lat, $long) = utm_to_latlon( 'clarke 1866', '30V', 12554, 41562 );
     70 * Plug-ins for CGI::Wiki and OpenGuides
     71   * CGI::Wiki::Plugin::Locator::UK
     72   * CGI::Wiki::Plugin::Locator::UTM