[xv,yv]=ginput;
xv = [xv ; xv(1)]; yv = [yv ; yv(1)];
in = inpolygon(x,y,xv,yv);
u=find(in==1 | in==0.5);
ess=mod_data(u);
v=find( ess > 0);
ess(v)=ess(v)-40;
mod_data(u)=ess;
h=pcolor(x,y,mod_data(:,:));
shading flat
v=[-40 40];