[Gnuplot-info] Draw rectangle on 3D surface

[GOO C. <goo...@gm...>]

Hi,

I'm trying to draw a simple rectangle on a surface graph. This is what I 
have:
/
/

    /set obj 1 rect at graph 0.5, 0.955 size 10, 5 fs transparent solid
    0.7 fc rgb "black" front//
    //set label 2 centre front "hello" at graph 0.5, 0.96 textcolor rgb
    "black"//
    //
    //set dgrid3d 100,100//
    //set pm3d//
    //splot inputfile u 1:2:3/


The label draw correctly, however the rectangle doesn't show. If I 
cahnge the surface to a heat map (set pm3d map), the rectangle shows. 
Also when drawing the rectangle on the surface with screen from and to 
coordinates, it also shows.

So my question: why doesn't the rectangle show when using either "at 
graph <position> size <size>"or "at screen<position> size <size>"? What 
am I doing wrong?

Chris