Project a face onto a terrain surface


I have attached a model that includes a solid made of a small section of a terrain created from contours, above which is a small curved face, representing the proposed top of a retaining wall. What I would like to do is extrude or intersect downward
the face directly onto the terrain, but not go through it. Can anyone tell me how to accomplish this? Thanks.050114-4 terrain mesh.skp (1.5 MB)


Extrude the retaining wall through the surface of the terrain.
Intersect the wall and terrain geometry.
Then erase what you don’t need.

Here’s a cleaned up copy of your model:
Retaining Wall.skp (219.8 KB)

Notice I exploded the terrain group and erased the bottom of the terrain model temporarily.

You need to work neatly in SU. Erase the masses of stray geometry and guides.
Delete all the layers, moving all geometry back to where it belongs on the Default Layer 0

Then learn about SketchUp Layers.
Does SketchUp Support Layers? — SketchUp Help w/Video

Intersect Command


That’s pretty much what the Drape tool does for a living:



Hey Gully, thanks for your response, you have helped me a couple of times already getting this terrain organized. What I was trying to do regarding the current post was not drape the face on the terrain, but project is downward onto the terrain without extending through. George responded that the way to accomplish it was to extrude the face through the terrain, intersect, and then trim off the parts not wanted. Anyway, thanks again.



Thanks George. I will work on this approach, still quite fuzzy on all the various options for intersecting objects. One thing I am confused by is your statement that all geometry should be moved on Layer 0. I come from a long cad background, and that is the only way to maintain flexibility in a project is through use of layers. I will review the layers link that you added to the post. Thanks again.


Ah, yes, then Geo’s method is what you want.

If you have Pro, you can save some time cleaning up by extruding the face, making the extrusion a (solid) group, and subtracting the terrain from the extrusion with the Subtract tool.



Thanks Gully, I will try using the Subtract tool.



I reviewed the layers video, and I think the scales have finally fallen from my eyes. After so much time with “traditional” cad, it was hard to get my head around this concept, but I have finally gotten it. Probably one of the most important but least emphasized/understood aspects of using SU. Thanks.


The stamp tool works well for this too, although it doesn’t behave well unless you give it an offset. So if you needed to extrude it straight down it won’t work. But with a slight offset, it works great.


Quick but not clean.
It’s pity there’s no way to could control the mass of unnecessary edges it creates.