How to subtract roads from terrain?

[corintho]

Hello! I have terrain created using height map (rendered with z-depth channel in 3ds Max).

I also have roads and streets created with standard tools (import DXF and polygonal street tool).

All streets aligned to terrain.

Now I need to create a hole in the terrain under the streets and lots.

I will place scatters on the terrain in 3ds Max. So roads must be subtracted from the terrain.

How to do this?

[MErikReedAugusta]

I'm not sure I follow.  Do you mean you want to Clip the terrain under the road polygons and replace those cells with NULL values?

If so, you'll probably want to start here:

https://support.esri.com/en-us/knowledge-base/how-to-clip-a-grid-to-a-specific-polygon-shape-0000182...

Note, of course, that any method of clipping a raster against a polygon will result in a mix of cells that have been included or excluded unevenly along the boundary of your polygon.  Depending on your cell size, this may or may not be a problem.

[corintho]

Hello, thanks for your reply. It seems that the suggested method is not suitable because your link is a tutorial on ArcMap software. I use CityEngine now... I will try to explain my question in more detail with screenshots.

Screenshot_1 shows my scene in CityEngine. As  you can see I   have 2  layers: roads and Terrain.

Screenshot_2 shows Terrain only (roads layer disabled). As you can see, the surface of the terrain under the road has not been subtracted. The surface of the Terrain is solid without holes. But I need to create holes under the roads in the terrain surface.

Screenshot_3 shows height map. Terrain was created based on this map. This is not real terrain, not from the real world. This is the planned state of the terrain. Therefore it is impossible to download this terrain from GIS software.

After I created the roads and aligned them on the terrain I need to create a hole in the terrain under the roads. I can't understand how to do this.

Screenshot_4 shows an example of what I should get. Terrain surface with a hole under the road.

[desert · Accepted solution]

Here are two ways you can approach this: duplicate the road layer, set its y-value to 0, select it, and use the 'align terrain to shape' tool to lower the terrain in the copied road's area; or, modify the heightmap data in 3D Max, noting that heightmaps use square cells, which can cause uneven terrain near the road depending on the cell size.

[JonasObertuefer]

Hi @corintho,

CityEngine does not support terrains with holes. However as desert mentioned you have many options to modify the terrain. The usual workflow is to

1. Align the shapes and streets to the terrain
2. Align the terrain to shapes

I recommend using the smooth border options for best results (See https://doc.arcgis.com/en/cityengine/latest/help/help-align-terrain-shapes.htm)

Cheers,
Jonas

[corintho]

Hello, thank you so much. I used the method by @desert and @JonasObertuefer I used 'align terrain to shape' tool. The result suits me