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5.1.1.2 Geographic coordinates

Figure 5.2: Linear transformation of map coordinates.
\includegraphics[]{eps/GMT_linear_d}

While the Cartesian linear projection is primarily designed for regular floating point x,y data, it is sometimes necessary to plot geographical data in a linear projection. This poses a problem since longitudes have a 360$^{o}$ periodicity. GMT therefore needs to be informed that it has been given geographical data allthough a linear transformation has been chosen. We do so by appending a d (for degrees) to the end of the -Jx (or -JX) option. As an example, we want to plot a crude world map centered on 125$^{o}$E. Our command will be 




gmtset GRID_CROSS_SIZE_PRIMARY 0.1i BASEMAP_TYPE FANCY PLOT_DEGREE_FORMAT ddd:mm:ssF
pscoast -R-55/305/-90/90 -Jx0.014id -B60g30f15/30g30f15WSen -Dc -A1000 -Glightgray -W0.25p -P \
    > GMT_linear_d.ps
gmtset GRID_CROSS_SIZE_PRIMARY 0




with the result reproduced in Figure 5.2.

next up previous contents index
Next: 5.1.1.3 Calendar time coordinates Up: 5.1.1 Cartesian Linear Transformation Previous: 5.1.1.1 Regular floating point   Contents   Index
Paul Wessel 2006-01-01