- Cassini projection
The Cassini projection is a
map projection described byCésar-François Cassini de Thury in1745 ["Flattening the Earth: Two Thousand Years of Map Projections", John P. Snyder, 1993, pp. 74-76, ISBN 0-226-76747-7.] . It is thetransverse aspect of theequirectangular projection , in that the globe is first rotated so the central meridian becomes the "equator", and then the normal equirectangular projection is applied. Composing these operations::x = arcsin(cos(phi)sin(lambda)),
:y = arctanleft(frac{ an(phi)}{cos(lambda)} ight)
where lambda is the longitude from the central meridian and phi is the latitude. When programming these equations, the
inverse tangent function used is actually theatan2 function, with the first argument sin(phi) and the second cos(phi)cos(lambda).The use of the Cassini projection has largely been superseded by the
Transverse Mercator projection, at least with central mapping agencies.Distortions
Things along the central meridian, and at right angles to it, are not distorted. Elsewhere, the distortion is largely in a north-south direction, and varies by the square of the central meridian. As such, the greater the longitudinal extent of the area, the worse the distortion becomes.
Due to this, the Cassini projection works best on long, narrow areas, and worst on wide areas.
References
External links
* [http://www.radicalcartography.net/?projectionref Table of examples and properties of all common projections] , from radicalcartography.net
* [http://www.ordnancesurvey.co.uk/oswebsite/freefun/geofacts/geo1164.html Ordnance Survey GeoFacts on the Cassini Projection]
Wikimedia Foundation. 2010.