Surface with minimum

Dear friends,

I encountered the problem of creation surface from curves where should be some minimum point somewhere there on surface (for example red cross, see attachment). The minimum should be in lower position then minimum points on the curves. Is such a the thing possible? How can I create such a surface, please.

Thank you for ideas & guides.

Surface with minimum.3dm (31.6 KB)

Hi Michal - does the attached make any sense with what you want?

Surface with minimum_PG.3dm (63.8 KB)


to me it looks like your curves resemble some duplicated trimmed boarder of an existing surface. at least it could be so, to rebuild that from the other direction is not so easy, at least one would have to find the tendency of each surface heading towards the cross.

here a few options

Surface with minimum.3dm (375.7 KB)

Hello guys,

all of your proposals are right. Great, thank you. Pascal is closest to the proper shape of the surface. Because my homework is create a two surfaces from curves with same minimum point as on the picture in attachment and space between the surfaces is empty instead of minimum point in the middle of the surfaces & minimum and maximum points on the edges of the curves. Well…and my goal have to be to learn how to do it. :slight_smile:


I suppose that Pasca created curves with same point (minimum point) and then created simple surfaces from each of the four areas. Am I right?

In case of the second surface could be used same procedure, right?

Correct - two InterpCrv curves through that minimum point, then split at that point as inputs to simple surfaces. Then some MatchSrf, for Tangency, with Average across the seams, then MatchSrf again for Position to the perimeter curves.


So the matching which I doing is because of smooth transit between each simple surfaces or because the simple surfaces will have character as a single surface…?

Why do I ask…, I realize that surfaces on the picture are two. In my case are surfaces four at the bottom and four at the upper.

Correct. But you should be able to MergeSrf > Smooth=No these surfaces and get a single surface if that is required.


Yes, it works. I tried use MergeSrf previously but I did not try Smooth=No. That is reason why does it not worked for me.

After MergeSurf one of the surface border line is still visible. Is there any way to remove it & get uniform surface with no line there?

Surface with minimum.3dm (181.3 KB)

Hi Michal - I would not merge in sequence ‘around’; try making two parallel merged surfaces and then merge these along the long edge.


Hello Pascal,

I spent a lot of time to merging of my surfaces but every time one surface remained.
Is there any other idea how to join the surfaces together to one surface?

Surface with minimum.3dm (393.8 KB)


Yeah, I see it is awkward with the kinks at the edges - see if the attached is something like what you want.

Surface with minimum_PG_Merged.3dm (81.5 KB)


That is it what I want to find. But what am I doing wrong (attachment). I created surfaces first time. Then I matched it to position & then I merged it in twice but from this step is not possible to merged it together because of gap between them.

Surface with minimum.3dm (256.1 KB)

Hi MIchal - this guy:

is the problem - see how the singularity is at the junction of the four surfaces - that will not merge nicely. Make that surface have the singularity down at the sharp angle on the outer curves, like so:

(This is one drawback to working in shaded modes if you have isocurves turned off - I always use wireframe, FWIW)


Hi Pascal,

I am trying again and again but I really do not know, how to do my isocurves in same shape as on your picture. When I create surface, the isocurves are created automaticly. I have no influence on their shape. I tryed move minimum point a little bit up and I adjusted centre cross curves a little bit straight but no success.