Looks like the Phantom 4 RTK is available in China DJI大疆精灵PHANTOM4 RTK 厘米级定位高清航拍航精准测绘无人机
A couple of videos on YouTube also showing the camera calibration using DJI assistant.
Found the manual online also talks about using the DJI base station or approved network for corrections.
WM334R1801...