Bonne's projection is a pseudoconical equal-area projection. The
meridians are represented by concurrent curves, the parallels by
concentric arcs of circles. The centre of the projection is defined as
the intersection of a straight central meridian with a central parallel
of length r0 = R*tan(90-lat0), where lat0 is the latitude of the central
parallel. The parallels are correctly spaced along the central meridian
and represented in correct length (which gives the projection the
equal-area property). Transformation formulae:
x = r*sin(T)
y = R*cot(lat0) - r*cos(T)
where
T = R*longit*cos(latit) / r
r = R[cot(lat0) - (latit - lat0)]
lat0 is the latitude of the central parallel.
R is the radius of the generating globe.
(setting the equator as central parallel yields sanson's sinusoidal
projection).
For more information see for example:
Canters, F. and H. Decleir, 1989, The world in perspective: a directory
of world map projections, John Wiley&Sons, Chichester.
___________________________________________
William De Genst
Centre for Cartography and GIS
Department of Geography
Brussels Free University V.U.B.
Pleinlaan 2
B-1050 Brussels
BELGIUM
Tel: ++ 32-2-629.35.56
Fax: ++ 32-2-629.33.78
http://www.vub.ac.be/DGGF
___________________________________________
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