【解决方案】 //通过layer3D拿到Layer3DDataset的Theme3DUnique,获取专题图图层
SceneControl sceneControl=new SceneControl();
Layer3D layer3D = sceneControl.Scene.Layers[0];
Layer3DDataset layer3DDataset= layer3D as Layer3DDataset;
Theme3DUnique theme3DUnique1= layer3DDataset.Theme as Theme3DUnique;