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Need help with gluUnProject

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Hey guys! Well, need some help with gluUnProject, but I'm guessing it's more to do with math. I'm doing a terrain editor. I have the following to render the scene:
void render()
		{
			Gl.glClearColor(173 / 255.0f, 192 / 255.0f, 255 / 255.0f, 255 / 255.0f);
			Gl.glClear(Gl.GL_COLOR_BUFFER_BIT | Gl.GL_DEPTH_BUFFER_BIT);

			Gl.glLoadIdentity();

			Glu.gluLookAt(camera.Position.X, camera.Position.Y, camera.Position.Z,
						  camera.Look.X, camera.Look.Y, camera.Look.Z,
						  camera.Up.X, camera.Up.Y, camera.Up.Z);

			terrain.Render(true);

			Glut.glutSwapBuffers();
		}

Basically it draws a terrain mesh loaded from a heightmap. Then I have the following to handle the mouse click:
void mouseHandler(int button, int state, int x, int y)
		{
			if (button == Glut.GLUT_LEFT_BUTTON && state == Glut.GLUT_DOWN)
			{
				var viewport = new int[4];
				var modelview = new double[16];
				var projection = new double[16];
				float winX, winY, winZ;
				double posX, posY, posZ;

				Gl.glGetDoublev( Gl.GL_MODELVIEW_MATRIX, modelview );
				Gl.glGetDoublev( Gl.GL_PROJECTION_MATRIX, projection );
				Gl.glGetIntegerv( Gl.GL_VIEWPORT, viewport );

				winX = x;
				winY = viewport[3] - y;
				// Read all pixels at given screen XY from the Depth Buffer
				var zzz = new float[16];
				Gl.glReadPixels(x, (int) winY, 1, 1, Gl.GL_DEPTH_COMPONENT, Gl.GL_FLOAT, zzz);
				winZ = zzz[0];

				Glu.gluUnProject(winX, winY, winZ, modelview, projection, viewport, out posX, out posY, out posZ);
			}
		}

And it works, just not as I'd want it to. I get the X,Y,Z position with relation to the camera, while I need the "real" coordinates. I'm guessing I have to do something with the matrices, but I'm not exactly sure what. Any help would be appreciated.

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Thanks for your reply! I ended up doing something they recommended there (each face a different color), so it works great now.

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