size(12cm,12cm);

import graph;
import palette;

int n=256;
real ninv=2pi/n;
real[][] v=new real[n][n];

for(int i=0; i < n; ++i)
  for(int j=0; j < n; ++j)
    v[i][j]=sin(i*ninv)*cos(j*ninv);

pen[] Palette=BWRainbow();

picture bar;

bounds range=image(v,(0,0),(1,1),Palette);
palette(bar,"$A$",range,(0,0),(0.5cm,8cm),Right,Palette,
        PaletteTicks("$%+#.1f$"));
add(bar.fit(),point(E),30E);

documentclass{article}
usepackage[pdftex]{graphicx}
usepackage[inline]{asymptote}
begin{document}

begin{figure}[!h]
begin{asy}
import graph;
import contour;
import palette;
defaultpen(fontsize(10pt));
size(14cm,8cm,IgnoreAspect);
// Load my height function:
file Z=input("dataZ.dat").line();
real[][] z= Z;
z = transpose(z);
pair xyMin=(1,74);
pair xyMax=(3,86);
// original function
real f(real x, real y) {return -2.051^3*1000/(2*3.1415*(2.99*10^2)^2)/(x^2*Cos(y)^2);}
int N=200;
int Levels=16;
defaultpen(1bp);
bounds range=bounds(-3,-0.10);
real[] Cvals=uniform(range.min,range.max,Levels);
// Original
// guide[][] g=contour(f,xyMin,xyMax,Cvals,100,operator --);
// Modified
guide[][] g=contour(z,xyMin,xyMax,Cvals,100,operator --);
pen[] Palette=Gradient(Levels,rgb(0.3,0.06,0.5),rgb(0.9,0.9,0.85));
for(int i=0;i<g.length-1;++i){
  filldraw(g[i][0]--xyMin--(xyMax.x,xyMin.y)--xyMax--cycle,Palette[i],darkblue+0.2bp);
}
xaxis("$x$",BottomTop,1,3,darkblue+0.5bp,RightTicks(Step=0.2,step=0.05),above=true);
yaxis("$y$",LeftRight,74,86,darkblue+0.5bp,LeftTicks(Step=2,step=0.5),above=true);
palette("$f(x,y)$",range,point(SE)+(0.2,0),point(NE)+(0.3,0),Right,Palette,
        PaletteTicks("$%+#0.1f$",N=Levels,olive+0.1bp));
end{asy}
caption{A contour plot.}
end{figure}

end{document}