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7.13 Plotting of vector fields

In many areas, such as fluid dynamics and elasticity, it is desirable to plot vector fields of various kinds. GMT provides a way to illustrate 2-component vector fields using the grdvector utility. The two components of the field (Cartesian or polar components) are stored in separate grid files. In this example we use grdmath to generate a surface and to calculate by returning the x- and y-derivatives separately. We superpose the gradient vector field and the surface z and also plot the components of the gradient in separate windows. A pstext call to place a header finishes the plot (Figure 7.13:

    #!/bin/sh
    #               GMT EXAMPLE 13
    #
    # Purpose:      Illustrate vectors and contouring
    # GMT progs:    grdmath, grdcontour, grdvector, pstext
    # Unix progs:   echo, rm
    #
    ps=example_13.ps
    grdmath -R-2/2/-2/2 -I0.1 X Y R2 NEG EXP X MUL = z.grd
    grdmath z.grd DDX = dzdx.grd
    grdmath z.grd DDY = dzdy.grd
    grdcontour dzdx.grd -JX3i -B1/1WSne -C0.1 -A0.5 -K -P -G2i/10 -S4 -T0.1i/0.03i \
            -U"Example 13 in Cookbook" > $ps
    grdcontour dzdy.grd -J -B1/1WSne -C0.05 -A0.2 -O -K -G2i/10 -S4 -T0.1i/0.03i -X3.45i >> $ps
    grdcontour z.grd -J -B1/1WSne -C0.05 -A0.1 -O -K -G2i/10 -S4 -T0.1i/0.03i -X-3.45i -Y3.45i >> $ps
    grdcontour z.grd -J -B1/1WSne -C0.05 -O -K -G2i/10 -S4 -X3.45i >> $ps
    grdvector dzdx.grd dzdy.grd -I0.2 -J -O -K -Q0.03i/0.1i/0.09in0.25i -G0 -S5i >> $ps
    echo "3.2 3.6 40 0 6 BC z(x,y) = x * exp(-x@+2@+-y@+2@+)" \
            | pstext -R0/6/0/4.5 -Jx1i -O -X-3.45i >> $ps
    rm -f z.grd dzdx.grd dzdy.grd .gmt*

Figure: Display of vector fields in GMT.

Next: 7.14 Gridding of data Up: 7. Creating GMT Graphics Previous: 7.12 Optimal triangulation of Contents Index