# Impossible to cut terrain surface with knife project tool

I am struggling to cut a terrain mesh with several triangles with the knife Project tool.

I defined the auxiliary geometry and selected the two entities, but when I apply the Knife Project button, I cannos see any face selected.

Thank you all in advance.

Best Regards

Jacob

• create a face for the cutting shape, how can knife know how it intersects the other shape...? Nov 21, 2017 at 16:15
• I've created a face for the cutting shape yet but I didnt get any result. Nov 22, 2017 at 8:59
• are you sure the two shapes have different Z levels (in order for "projection" to work)? Nov 22, 2017 at 9:43
• The cutting shape is plane, so it should be projected to terrain to make an efective cut? Nov 22, 2017 at 11:54
• I attach the link of the file if this can help:drive.google.com/open?id=1qHwGinegnqCVw7nbnY3p_2cOQ35Mxxdl Nov 22, 2017 at 13:26

## 2 Answers

I tried your STL file, imported (and scaled it down to the grid size, about .0001) then recalculated normals (face normals pointing up to +Z).

Then added a simple plane (4 verts, face normal points up to +Z)

Placed the plane somewhat above the STL map

then selected the plane, and after also the map, entered edit mode and from ortho top view uset "knife project":

after hiding the plane:

imho, it should work, in this way...

• I have followed your steps carefully. In edit mode, I recalculate the normals in z positive direction for the two entities. Unfortunately, I didn't get any selected face. Anyway, I solved partially my problem by using the boolean modifier. Thank you very much. Nov 23, 2017 at 12:33

Two reasons you can't "K"cut. Normal's are flipped, so try cutting on the other side of the face. And/or the mesh is so dense that the knife can not map to the faces. You need to zoom in to cut from vertex to vertex. Or try a decimation modifier to simplify the geometry.

• The mesh have 155000 faces approximately. I've tried to cut in the other side but it stills doesn't make anything. Nov 22, 2017 at 11:17
• I also tried to zoom in some faces to cut parts of the mesh, but it still dont know what is failing. Nov 22, 2017 at 11:33
• I attach you the link of the stl mesh file if this would help. Thank you. drive.google.com/open?id=1qHwGinegnqCVw7nbnY3p_2cOQ35Mxxdl Nov 22, 2017 at 13:29