TIN图层设置透明度问题

<P>我用AO生成了一个Tin网格，用TinElevationRendererClass渲染后，给渲染涂层加上透明度，代码如下：</P>
<P>            pTinRendearer.Tin = itinadvanced as ITin;<BR>            pTinRendearer.Visible = true;<BR>            tinlayer.AddRenderer(pTinRendearer);<BR>            tinlayer.SpatialReference = this.axSceneControl1.Scene.SpatialReference;<BR>            //设置显示效果<BR>            ((ILayer)(tinlayer) as ILayerEffects).Brightness = 90;<BR>            ((ILayer)(tinlayer) as ILayerEffects).Contrast = 100;<BR><FONT color=#ff0000>            if (((ILayer)(tinlayer) as ILayerEffects).SupportsTransparency)<BR>                ((ILayer)(tinlayer) as ILayerEffects).Transparency = 90;//设置透明度</FONT><BR>            this.axSceneControl1.Scene.AddLayer((ILayer)(tinlayer), true);</P>
<P>生成图层后显示在arcscene控件里，可以看出透明度设置生效。但是当我放大，缩小地图时，这个Tin图层透明度失效，变为不透明的了！不知这是问什么？大家能否解答一下！</P>