Nullify elevation in GDALImageLayer about osgearth HOT 1 CLOSED

<map>
    <ContourMap/>
    <TMSImage name="Floating imagery" opacity="0.5" altitude="25000">
        <url>http://readymap.org/readymap/tiles/1.0.0/7/</url>
        <shader>
          <![CDATA[
            #pragma vp_function func1, vertex_view, 0.0
            vec3 save;
            void func1(inout vec4 vertex) {
              save = vertex.xyz;
            }
            [break]
            #pragma vp_function func2, vertex_view, 1.0
            vec3 save;
            vec3 oe_UpVectorView;
            uniform float oe_terrain_altitude;
            void func2(inout vec4 vertex) {
              vertex.xyz = save + oe_UpVectorView * oe_terrain_altitude;
            }            
          ]]>
        </shader>
    </TMSImage>
    <TMSElevation name="ReadyMap 90m Elevation">
        <url>http://readymap.org/readymap/tiles/1.0.0/116/</url>
        <vdatum>egm96</vdatum>
    </TMSElevation>
</map>