function a = DrawGraph(X,Y,Z,XCurtain,YCurtain,ZCurtain,ViewP)

	% Draw a surface model version of the data.

h = surf(X,Y,Z);
set(h,'MeshStyle','column');
%surfl(X,Y,Z);

	% Set properties of axes.
	
v = axis;
axis( [-80 80 -80 80 0 v(6)] );
axis('square');
set(gca, 'XTick', [-80 -40 0 40 80]);
set(gca, 'YTick', [-80 -40 0 40 80]);

if ViewP(1,2) ~= 90
	ViewP(1,2) = 35;
	end;
	
view(ViewP);
	

	% Freeze the axes.
	
axis(axis);

	% Set so drawing occurs on the current axes not a new
	% set of axes.
	
hold on;

	% Draw 0, 90, 180, and 270 degree lines.
	
x1=[-75;75];
y1=[0;0];
plot(x1,y1);
	
x1=[0 0;0 0];
y1=[-75 0;0 80];
plot(x1,y1);

	% Draw circle at zenith angle of 76 degrees.

t=0:.05:2*pi;
x = 76 * cos(t);
y = 76 * sin(t);
plot(x,y);

	% Draw the curtain lines for the view zenith angle strips.

if ViewP(1,2) ~= 90
	h = plot3(XCurtain, YCurtain, ZCurtain);
	set(h,'Color',[1,.5,0]);
	
	end;	% if ViewP(1,2) ~= 90
	
hold off;
