5.4.5 Cassini Cylindrical Projection (-–Jc -–JC)

This cylindrical projection was developed in 1745 by C. F. Cassini for the survey of France. It is occasionally called Cassini-Soldner since the latter provided the more accurate mathematical analysis that led to the development of the ellipsoidal formulae. The projection is neither conformal nor equal-area, and behaves as a compromise between the two end-members. The distortion is zero along the central meridian. It is best suited for mapping regions of north-south extent. The central meridian, each meridian 90$^{o}$ away, and equator are straight lines; all other meridians and parallels are complex curves. The requirements to define this projection are:

$\bullet$

Longitude and latitude of central point

$\bullet$

Scale in inch/degree or as 1:xxxxx (-Jc), or map width (-–JC)

A detailed map of the island of Sardinia centered on the 8$^{o}$45’'E meridian using the Cassini projection can be obtained by running the command:

#!/bin/sh
#    $Id: GMT_cassini.sh,v 1.1 2001/03/21 04:10:21 pwessel Exp $
#

gmtset LABEL_FONT_SIZE 12
pscoast -R7:30/38:30/10:30/41:30r -JC8.75/40/2.5i -B1g1f30m -Lf9.5/38.8/40/60 -Dh -G200 -W0.25p \
   -Ia/0.5p -P > GMT_cassini.ps

Figure 5.22: Cassini map over Sardinia

As with the previous projections, the user can choose between a rectangular boundary (used here) or a geographical (WESN) boundary.