Azimuthal equidistant projection
The azimuthal equidistant projection is a type of map projection. A useful application for this type of projection is a polar projection in which all distances measured from the center of the map along any longitudinal line are accurate; an example of a polar azimuthal equidistant projection can be seen on the United Nations flag.
This projection is used by the USGS in the National Atlas of the United States of America, and for large-scale mapping of Micronesia. It is useful for showing airline distances from center point of projection and for seismic and radio work.
Distances and directions to all places are true only from the center point of projection. Distances are correct between points along straight lines through the center. All other distances are incorrect. Distortion of areas and shapes increases dramatically, the further away one gets from center point.
Some types of wide-angle camera lenses, known as "fisheye lenses" produce an azimuthal equidistant projection of the photographed scene onto the photographic medium. These lenses allow a much wider field of view than perspective lenses, which are limited to significantly less than 180 degrees.
[edit] History
While it may have been used by ancient Egyptians for star maps in some holy books,[1] the earliest text describing the azimuthal equidistant projection is an 11th-century work by al-Biruni.[2]
In some countries this projection is named "Postel projection" after Guillaume Postel, who used it for a map in 1581.[1]
[edit] References
- ^ a b SNYDER, John P. (1997). Flattening the earth: two thousand years of map projections. University of Chicago Press. ISBN 0226767477., p.29
- ^ David A. KING (1996), "Astronomy and Islamic society: Qibla, gnomics and timekeeping", in Roshdi Rashed, ed., Encyclopedia of the History of Arabic Science, Vol. 1, p. 128–184 [153]. Routledge, London and New York.
[edit] External links
- Table of examples and properties of all common projections, from radicalcartography.net
- Online Azimuthal Equidistant Map Generator
- An interactive Java Applet to study the metric deformations of the Azimuthal Equidistant Projection.
- GeographicLib provides a class for performing azimuthal equidistant projections centered at any point on the ellipsoid.
- Concept and mathematics of the Azimuthal Equidistant Projection for the marine navigator.
