In the world editor, heightmap files are imported so they can be applied using the brush. This visual method does not allow to have a full control over the height of each point in the resulting terrain.
Is it possible to make the engine use the heighmap file (raw or image) as heightmap for the terrain without need for editing with the level brush ?
I want to apply my heightmap file to the terrain and i only need to scale it.

I don't know from memory what the exact resolution of a heightmap is, but if you make sure you have a 1 to 1 mapping with your image, it should be exactly the same. I've used this more than once with good results.
Of course, if you scale it wrong, it won't be good. It's a bitmap, not a vector graphic.

I tried to use your method but the problem is still the same, I still have to use the brush to apply the heightmap image. The height is determined by the duration of the click which I cannot control perfectly.
What I want to achieve is ti have the same proportions of heights in the terrain as in the heightmap. I only want to scale my image horizontally and vertically to determine the maximum height and the area that it will cover from the terrain.

menu/heightmap/import height?