Polysurface offsetting

Hi everyone,
New to this forum and looking for some help with a project. I have this surface that offsets in a weird way. my aim is to have a variable offset of the three surface together so i can use a grasshopper script to convert it in into a egg crate structure.
Please do note the surfaces dont need to be too accurate but just merge together well and keep its general shape.

i did try using rebuild surface, match surface, merge surface and blend surface. but didnt work.

Thanks for the help.

eggcrating1.gh (16.5 KB)
surfaces.3dm (738.7 KB)


The isocurves on your top surface come to a sharp point at that corner. You can get a clean solid from an offset by extending the top surface to square off the end so you don’t have the sharp point, extruding and then using the curve of your original surface to Boolean split the solid.

Roof 2.3dm (1.2 MB)

ExtendSrf did not want to play so I created contours of one half of your surface and extended the contour curves, then created a new boundary curve from their ends and extended your roof’s side curves (see the red items). I used the three curves as edge curves to make a new surface, picking the curved side first (this gives the best isocurve alignment for our purposes). This could be offset and mirrored to make the new roof (the green item). There were some artefacts down the centreline of the lower surface that needed cleaning up so I finished with a quick explode, tidy and rejoin.

Hope that helps



Thank you so much Jeremy, you saved me hours of going back and forth. I didnt know surface through edge curves works with non planar curves.
Just one more thing when i offset i am getting these weird artefacts as you mentioned but not sure how do i tidy them up. What method did you end up using. I can apply that to the other surfaces as well.

Hi Salman,

I’m not absolutely certain which part of the model is appearing in your image. If it is, as I suspect, showing a half section before mirroring, on the centreline, then you have the isocurves oriented differently from my reworking and still coming to a point and that is causing the artefact shown. If you look at my top surface you will see that my isocurves are more following the edges. The orientation is dependent on the order you select the edge curves to make your surface. Try picking the three edges in different orders until you match the layout in mine. Then when you offset you will avoid the self-intersecting edges.

As for cleaning up, the artefacts I got were either spurious vertical faces down the central underside or tiny gaps where the offset lower surfaces didn’t quite meet in the middle after mirroring (the type of artefact depended on the order in which I did things and I don’t recall which arose when). To clean up I started by exploding the complete roof so I could work on its individual surfaces. Spurious surfaces I deleted. Gaps down the centre I filled by extending the surface (ExtendSrf did work in this case) on each side of the gap beyond the centreline and trimming back with a line down the centre. There was an associated V-shape gap down the middle of the rear (concave) surface, so I deleted the surface and used the top and bottom edges as rails to sweep2 between the side edges to create a replacement face. Finally, I joined the faces again to recreate a closed solid.


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Fantastic Jeremy,
I tried it and it worked on my end. Thank you so much it was a life saver

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