Terrain from imported houdini heightmap appears pixelated

Hi folks, I don’t know why the generated terrain from houdini looks very weird in UE4.
II create the terrain in Houdini first (following the Houdini foundation PDF) and then exported height map(attached here:https://www.dropbox.com/s/zaawqjhm3o…htmap.zip?dl=0
) and layer masks to 4K-16bit-int maps.

Then I use these 4k maps to create UE4 terrain and layer info.

The UE4 terrain resolution is 4310*4310

I can see that the terrain has a pixelated surface, but in Houdini it is smooth.



I think it is caused by the unfit between the size of imported heightmap and terrain resolutions. One pixel in the imported png map fills one or more grids in the terrain. Does Unreal scale down or up the heightmap to match the resolution of the terrain? Or it just simply clip/expand it?
If so, how can I drive a terrain with a heightmap whose resolution is much higher to prevent the pixelated results?

If this is not the root cause of the problem, then what is the real factor that controls the smoothness of the terrain?
And, how can I drive a low-resolution terrain with a much higher resolution heightmap?