itwin.js load RealityModel error

Hi boys:

        I have same problems when use itwin.js load realityModel. The specific operation is as follows:

        1、 I use DgnV8Converter 2.0 to convert .3sm to 3dTiles.

        2、Publish it as a web service using nginx.

        3、Use itwin.js to load this service.

        With there steps, it's seems no problem happened. But, i didn't set up Coordinate System. So, i cann't get the Latitude and longitude in itwin.js.

        Then, i have set the Coordinate System in .3sm, and translate it to .b3dm. Now, when i load this realityModel , it looks inclined. like this flower picture:

 ,

                    With this problems , i use cesium.js to load there 3dTiles. I divided the data into two parts, one with the geographic coordinate system set, and the other without the geographic coordinate system.At the same time, in order to better observe the 3dTiles data loading, I made the following settings in Cesium.js:

                    1、dModel.debugShowContentBoundingVolume = true;

                    2、 add 3dtiles to entities. like this:

modelDtiles.tileVisible.addEventListener(function(tile){
viewer.entities.add({
position: new Cesium.Cartesian3(tile.boundingSphere.center.x,tile.boundingSphere.center.y,tile.boundingSphere.center.z),
point:{pixelSize:10,color:Cesium.Color.RED}
});
})

                   And then, I found this problem:

                  1、if 3dtiles dinn't have geographic coordinate system , the realityModel is inclined.

                 2、if 3dtiles have geographic coordinate system , the .b3dm file have been loaded,but didn't see in screen.

                       

            How should I solve the above problems ? Please help me, thanks.