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## 6.3.5 Cassini cylindrical projection (-Jc -JC)

This cylindrical projection was developed in 1745 by César-François Cassini de Thury 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° away, and equator are straight lines; all other meridians and parallels are complex curves. The requirements to define this projection are:

- Longitude and latitude of central point.
- 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°45'E meridian using the Cassini projection can be obtained by running the command:

    pscoast -R7:30/38:30/10:30/41:30r -JC8.75/40/2.5i -B1g1f30m -Lf9.5/38.8/40/60 -Dh -Glightgray \
            -Wthinnest -Ia/thinner -P --LABEL_FONT_SIZE=12 > GMT_cassini.ps

Figure 6.19: Cassini map over Sardinia.

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

Next: 6.3.6 Cylindrical equidistant projection Up: 6.3 Cylindrical projections Previous: 6.3.4 Oblique Mercator projection Contents Index