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 grdfiles. 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:
#!/bin/csh # GMT EXAMPLE 13 # # $Id: job13.csh,v 1.4 2003/12/18 02:27:21 pwessel Exp $ # # Purpose: Illustrate vectors and contouring # GMT progs: grdmath, grdcontour, pstext # Unix progs: echo, rm # 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" >! example_13.ps grdcontour dzdy.grd -J -B1/1WSne -C0.05 -A0.2 -O -K -G2i/10 -S4 -T0.1i/0.03i -X3.45i >> example_13.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 \ >> example_13.ps grdcontour z.grd -J -B1/1WSne -C0.05 -O -K -G2i/10 -S4 -X3.45i >> example_13.ps grdvector dzdx.grd dzdy.grd -I0.2 -J -O -K -Q0.03i/0.1i/0.09in0.25i -G0 -S5i >> example_13.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 \ >> example_13.ps \rm -f z.grd dzdx.grd dzdy.grd .gmt*
A pstext call to place a header finishes the plot (Figure 7.13.