C#

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float maxint = maximum intensity in your 2d terrain.<br />
float minint = minimum intensity in your 2d terrain.<br />
float scale = maximum altitude/maximum intensity in 2d terrain.<br />
float zscale = scale*(maxint-minint)<br />
for each x and y in 2d image <br />
float dx= intense2d(x+1,y)-intense2d(x,y), dy=intense2d(x,y+1)-intense2d(x,y);<br />
//Your normal would be the cross product of dx and dy as vectors<br />
//Vector and cross product you define yourself of course.<br />
Vector norm = cross(new Vector(1,0,dx), new Vector(0,1,dy)); <br />
Gl.glNormal3f ( (float)norm.x, (float)norm.y, (float)norm.z );<br />
// set the color if you haven't alreayd<br />
//Gl.glColor3f(rcolor,gcolor,bcolor);<br />
Gl.glVertex3f ( (float)x, (float)y, (float)intense2d(x,y)/(zscale)); 

private void ProcessResponse(System.IAsyncResult state){<br />
HttpWebResponse linkpage=(HttpWebResponse)((HttpWebRequest)state.AsyncState ).EndGetResponse(state);<br />
StreamReader stream = new StreamReader(response.GetResponseStream());<br />
string  info = stream.ReadtoEnd();//2 threads blocked here<br />
stream.Close()<br />
response.Close();