I have a setup where I do the following:
- heightfield node where I import an existing heightmap.
To match the ingame scale the height scale is set to 768. As far as I know, this is only for the visual reference in the viewport, and does not reflect what will actually be exported.

In the setup I use curves and sweep to make roads. I use the same data to flatten along the curve, so the road will fit perfectly in place.

In the end I export the resulting heightmap.

The issue is the values are in general different from the original. So when I bring the new heightmap into the engine/editor, the entire terrain is lifted a little, thus trees, rocks, other roads and buildings are buried.

In the heightfield output I've set
Output type: Packed Raster
Format: Single Channel
Type: 16b Fixed

Output Range: Auto Remap
To range: 0 | 1


I have tried different ranges, and currently 0 | 0.987 seems to get me close, but still some deviation.
I'm at a loss of what to do or how to figure this out.

Ideally I'd like to have a 1:1 input-output, and only manipulate where the road goes.

Fairly new to Houdini as well, so please talk to me accordingly.

After a lot of trial and error, I think I'll just stick to fine tuning manually.. This will probably have to be fine tuned for other maps with less elevation differences I presume.