surface transparency

Hello, All

I used Gridded2DSet to draw a topography surface. I also want to draw some street lines on the surface. Each street line has some points with only x and y, I used valueToInterp method to interpolate these points to get z values, then draw these points as one line. My problem is, some segment of the line are below the surface. So I want my topography surface to be transparent so that every thing below the surface can be seen clearly. I tried the following:

dispGMC = (GraphicsModeControl)display.getGraphicsModeControl(); 

zMap   = new ScalarMap(Z, Display.RGB);
display.addMap(new ScalarMap(Z, Display.Alpha));

Now the surface I got is opaque. I do not know how to set the Alpha value.

Any help will be highly appreciated.

Gaoming Fu

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