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| Benefon Esc! - Grids & Datums |
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What is a projection?
Projection is a method of representing the earth's three-dimensional surface as a flat
two-dimensional surface. This normally involves a mathematical model that transforms
the locations of features on the earth's surface to locations on a two-dimensional
surface. Because the earth is three-dimensional, some method must be used to depict
the map in two dimensions. Therefore, such representations distort some parameter
of the earth's surface, be it distance, area, shape, or direction.
There are a variety of map projections, but all are generally of three basic
types; these are the Azimuthal, conical and cylindrical projections.
What is a grid?
Most maps have a grid of some kind marked on them, lines that crisscross the map
in two directions. The most common is the latitude and longitude system, usually
marked in degrees. The easiest way to depict a point on a two-dimensional map is
with two lines that cross. Where they cross is the location of the point you are
interested in the campsite, the waterfall, or where you are standing at a given point in time.
Grids supported in Esc!
HDDDºMM'SS.S"
HDDDºMM.MMM'
HDDD.DDDDDº
BRITISH GRID (BNG), GERMAN GRID (GK), IRISH GRID (ITM), NEW ZEALAND GRID (NZG),
SWEDISH GRID (SG), SWISS GRID (SUI), TAIWAN GRID (TG), UTM, USER UTM GRID (USR).
What is a datum?
Datum is a mathematical model of the earth used to calculate the coordinates on a map.
This includes a set of defining parameters, which forms the basis for computing positions
on the surface of the earth. These parameters include the dimensions of a reference
ellipsoid and the coordinates of a point of origin. Most datums are created for use
only in specific areas of the earth, but the World Geodetic Systems (WGS) can be
used globally.
Datums are important because to accurately represent horizontal positions on maps
and charts, we need a mathematical model of the earth that takes into consideration
the size and shape of the earth.
Datums supported in Esc!
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AIN EL ABD: Kuwait; Saudi Arabia |
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AGD66, AGD84: Australia; Papua New Guinea |
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ARC 1950, ARC 1960: Africa - south |
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CAPE: South Africa |
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CH 1903: Switzerland |
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CORREGO ALEGRE: Brazil - NE coastal area between 45º W and 40º W |
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EUROPEAN 1950: Austria, Belgium, Denmark, Finland, France, Germany, Gibraltar,
Greece, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland
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EUROPEAN 1979: Austria, Finland, Netherlands, Norway, Spain, Sweden, Switzerland |
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FINLAND HAYFORD: Finland |
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GD49: New Zealand |
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HJORSEY 1955: Iceland |
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HONG KONG 1963: Hong Kong |
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INDIA BANGLADESH: Bangladesh, India, Nepal |
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INDIA THAILAND: Thailand, Vietnam |
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INDONESIA 1974: Indonesia |
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IRELAND 1965: Ireland |
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KERTAU: West Malaysia, Singapore |
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LUZON MINDANAO: Mindanao Island |
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LUZON PHILIPPINES: Philippines excl. Mindanao Island |
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NAHRWN MASIRAH: Oman - Masirah Island |
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NAHRWN SAUDI A: Saudi Arabia |
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NAHRWN UAE: United Arabic Emirates |
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OLD EGYPTIAN ´07: Egypt |
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OSGB: England, Isle of Man, Scotland, Shetland Isles, Wales |
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PROV SA ´56: South America |
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PROV S CHILE ´63: South America |
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RT90: Sweden |
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STH AMERICA 1969: Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Guyana,
Paraguay, Peru, Venezuela, Trinidad&, Tobago |
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SOUTH ASIA: Singapore |
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WGS72, WGS84: World |
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USER DATUM |
What is the benefit for the user?
Different maps and charts use different position formats. Grids and Datums support
allows the user to choose the correct system for particular purpose.
It is important to know which datum is being used on a map, because the
coordinates for a point on the earth´s surface in one datum will not
match the coordinates from another datum for that same point.
User datum for Finnish (YKJ grid):
DX: -78 m
DY: -231
DZ: -97 m
DA: -251 m
DF: -0.1419270
User grid for Finnish (YKJ grid):
Longitude origin: E027.00.00
False easting: +03500000.0
False northing: +00000000.0
Scale: +1.00000000
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