5 Replies Latest reply on May 8, 2017 3:04 PM by Dan Pihlaja

# Why can't 3 surfaces sharing a common edge be knitted together ?

Hi,

What is the logical reason behind this? (or is it possible and I don't know?)

In below illustration I can knit any 2 surfaces together. But when i try to knit all 3 surfaces together or 2 surfaces at once and then knitted surface with the third surface it throws error. All the three surfaces share a common edge.  Practical application is when I try to knit the 'tent-like' surface on top of base surface the error appears (there surfaces - split face, base surface and tent-like surface have a  common edge). But I can knit if i delete the split surface before making the tent-like surface. • ###### Re: Why can't 3 surfaces sharing a common edge be knitted together ?

Sachin,

I don't use surfaces that much but I don't think you can have more than two surfaces knitted at a common edge. That is what comes up as an error message when I tried to do it. • ###### Re: Why can't 3 surfaces sharing a common edge be knitted together ?

Here is another way of doing something very similar.   It is a hybrid of solids and surfaces.   Maybe it will work for you as well.

SW 2015 SP 5

• ###### Re: Why can't 3 surfaces sharing a common edge be knitted together ?

thanks Dan for showing another method. I can already see where this can come handy.

Similar to Euler's Formula  which relates number of faces, vertices and edges for any non-intersecting polyhedron is there any formula that governs surfaces. Is it the because of this criteria we cannot create 3 surfaces sharing  a common edge? Just curious to know.

• ###### Re: Why can't 3 surfaces sharing a common edge be knitted together ?

Not sure....but according to some of the things that I have read, 3 surfaces sharing a common edge violates this formula:

https://www.cs.mtu.edu/~shene/COURSES/cs3621/NOTES/model/euler.html

EDit:  Sorry, I forgot to add it....I meant to include some bits copied from that website:

Here it is: The Euler-Poincaré formula describes the relationship of the number of vertices, the number of edges and the number of faces of a manifold. It has been generalized to include potholes and holes that penetrate the solid.  To state the Euler-Poincaré formula, we need the following definitions:

• V: the number of vertices
• E: the number of edges
• F: the number of faces
• G: the number of holes that penetrate the solid, usually referred to as genus in topology
• S: the number of shells.  A shell is an internal void of a solid.  A shell is bounded by a 2-manifold surface, which can have its own genus value. Note that the solid itself is counted as a shell.  Therefore, the value for S is at least 1.
• L: the number of loops, all outer and inner loops of faces are counted.

Then, the Euler-Poincaré formula is the following:

V - E + F - (L - F) - 2(S - G) = 0
• ###### Re: Why can't 3 surfaces sharing a common edge be knitted together ?

Can you ask yourself a question: does it make sense to you if these 3 surfaces are knitted together to create one? What you expected the result after knitting these surfaces ?