Although some people today still think otherwise, our planet is not flat, so any attempt to represent the Earth on a plane needs some kind of transformation, known as map projection. In this process, there is always a compromise between the properties that get preserved and others that get deformed, any map projection therefore always has some kind of distortion. The Tissot's Indicatrix is a plot that contains circles at grid intersections and shows how they vary due to distortion Depending on what the map is needed for, one projection may be better than another, and there are lots of different map projections that can be classified by two main criteria:
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Tissot's Indicatrix for Mercator projection |
The Mercator map projection was created by Gerardus Mercator in 1569. This projection is cylindrical and conformal, so local angles are preserved and local circles are not deformed. Distortion is constant along any parallel and constant bearings (rhumb lines) are straight lines. The map extends infinitely north and south. This is the projection used in Google Maps and by extension, all websites fed by them, including Vortex interface The Universal Transverse Mercator however, is not a single map projection but a system that divides the Earth into sixty zones, each being a six-degree band of longitude (numbered from 01 to 60, west to east). These bands are divided into cells eight-degrees high of latitude (specified by a letter from A to X, south to north, with N being the first letter north of the equator.) A position on the Earth is given by the UTM zone number and the easting (x Cartesian coordinate) and northing (y coordinate) in that zone. |
Another way to transform geographic coordinates to UTM is by using the Geospatial Data Abstraction Library (GDAL). This Open Source library can transform any coordinate system referenced to any datum. A couple of UTM coordinates (utmx, utmy) can be converted to a geographical latitude and longitude by typing:
> gdaltransform -s_srs EPSG:ZONE -t_srs EPSG:4326 utmx utmyWhere the parameter ZONE depends on the UTM zone and can be obtained from http://spatialreference.org
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