[CONNECT C#] How to get the correct texture coordinates?

For some reason, I'm trying to extract the geometry and material information of elements into OBJ format.

Everything was going well until I tried to attach the texture to the geometry.

As we all know, we should attach the texture to the geometry by using UV coordinates.

I get the geometry information of an Element by using ElementGraphicsOutput and ElementGraphicsProcessor, and then get the UV coordinates from PolyfaceHeader.Parameters in the processing result, which contains a list of PolyfaceHeaders.

But the finally result looks not good.

It's the original one in MicroStation:

This is the result when using the UVs from the PolyfaceHeader.Parameters.

I think that there must be some method to generate the correct UVs by using the MapUnits and MapMode (two parameters which affect the mapping result):

Can anyone help me?