MODELLING HELP: sundial gnomon and curves

Hey guys,

I’m currently working on a project of a sundial and I’m having problems modelling the gnomon (time indicator).
I have defined the curves of the contours of the gnomon but I don’t know how to establish the additional curves to make a 3d shape. I can do it very arbitrary, trying my best for the nicest shape, but i feel in my guts that there must be a better method to find the optimum.
So far I have tried “sweep2” but the results are strange (though satisfying in some parts) and surface from network of curves (but I still have to give the 3rd curve, and I feel like I’m lacking control over ther process).

Could anyone suggest a method to how to apporach this issue? Thanks!!!

Hi @Bed
Without having the actual curves - which is always a nice addition when asking for help, because it makes it so much easier to help, so please post them - my initial thought would be to use loft instead. You could also try to mirror and join the cross sections, so that you have the full “circle” - that might help you avoid the dip in the surface (make sure that the curves are tangent across the center!).
HTH, Jakob

Hi Jakub, thanks for your reply.

Lofting was my first thought, though I can’t reply apply it here cause upper and lower profiles must follow the rails of the lateral curves.

And, yes, thanks for advice, I attach my 3dm file.
zs24.3dm (1.1 MB)

When it comes to organic NURBS shapes like that, nothing can beat the quality, simplicity and History-enabled modification that Loft with the “Loose” option provides. The closest rival to Loft is SubD.
A good practice is to use profile curves with the same degree and amount of control points. The file attached here has an active History, so you can further adjust the shape of the Loft surface by moving/scaling the profile curves or their individual control points.
I started by creating the round base by using the Circle command with the “Deformable” option and 8 control points. The profile curves above were modified versions of the deformable circle.
I built the object in the center of the World coordinate, far away from your original objects that were not in the center.

zs24 Bobi.3dm (1.3 MB)

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Hey Bobi,

this is amazing, exactly what I needed! Thank for the model and for the good advice!

Could you tell me once more how exactly did you find these intermediary curves? Did you modify the starting circle arbitrarily or did the software find the stages between the circle and the top profile?

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When I created the initial circle at the base, I simply copied it a few times and then modified each individually by moving its control points in the desired location. I also used Scale 3D and Scale 1D to adjust the overall size of each profile curve. As I moved or modified each intermediate curve, the History-enabled Loft surface updated in real-time, thus it let me decide what changes I needed to make to achieve a shape which is close to the original curves you had.

There is a 4K/60 video tutorial that I made for you which I uploaded on YouTube, but it’s still being processed, so check back here for an update after a couple of hours when it’s ready.

All clear, thanks again for the explanation.

And really wow.
First time I’m posting on this forum and I have to say that the community is amazing

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That’s correct, this community is the best you can find on the net! :slight_smile: It’s a pleasure to be part of it.

Here is the video tutorial with the lower resolution. A version with 4K resolution should be ready in about one hour. Keep in mind that in this example I used the “Normal” option of Loft, which is not a good way to do the shape you wanted. The video capture was interrupted for some reason and stopped far earlier, so you will not see how I then deleted the initial loft surface and created a new one using the “Loose” option, which is the correct way for shapes like that. This is exactly I uploaded in the 3dm file in my previous post above.

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Thanks! :clap: :clap: :clap: :clap:

Hey Bobi,

I was working on refining the final model for the production. Loft works nicely until a closer examination when some surface problems occur…

In order for the sundial to work, its upper part must stay planar (red lines) but I’d like to have a nice blend between the circular base (blue) and the planar gnomon. And I feel I’m almost there!
But looking up close, there are some artifacts showing on, probably generated by lofting…
I also want the edges to have a slight fillet but it looks like it messes up the model… I wonder Is lofting still the best option to get smoother edges and a nice blend with the base? It all kind of works, but I’m really curious what would be the best approach.
Zs24_almostfinal.3dm (8.0 MB)

I actually would love to get some similar vibe in terms of blending (a little bit less organic though) as in this project

As I mentioned above, for this kind of organic shapes “Loft” works best when the “Loose” option is being used instead of “Normal”. :slight_smile: I noticed that you are using the “Normal” option and this is what causes some bad areas on your model. Keep in mind that the lofted shape while using the “Loose” option will NOT follow the profile curves used to build it. Instead, the lofted surface will have its control points placed in the exact same location as the control points of the profile curves. This is why “Loose” is so powerful when it comes to building very clean and quality lofted surfaces. :slight_smile:
Also, you use profile curves with different amount of control point, whereas my recommendation was to use curves with exactly the same degree and control points.

Thanks, but I’m actually using “loft” with “loose” option on…

The issue is caused by the use of profile curves with totally different structure. Some of your curves have 7 control points, others have 8 control points, others have 11 control points. On top of that, your curves have a different number of segments, because they were built by joining several open curves into a single one. Also, your circle base is an open curve (run the “What” command to check it) while the others are closed. The base curve was originally a degree 2 circle whose back end you split and then added and joined a small curve to it to make a closed polycurve with degree 3. Your 2nd and 3rd curves (the ones below the top curve) have two sharp crease corners each, while the 4th and 5th curves below have a single crease at the opposite end. Your top curve has two creases at the sharp edges, along with two duplicate control points there. All of these variables produced errors with the lofted surface.
If you follow my tutorial and use curves with the same degree and control point count, your lofted surface will be perfect. :slight_smile:

Got ya! Will do, thanks again!