Can't merge trimmed edges of surfaces

Hi guys,

I need your help. I wonna merge three surfaces but it doesn’t work and I don’t know what to do.

merge trimmed edges of surfaces.3dm (1.3 MB)

Thank you for your help :slight_smile:


Correct, only untrimmed edges can be merged along untrimmed edges. That is inherent in the math used for the surfaces.


a) Join the surfaces into a polysurface.

b) Build a single surface using the available data. This is not always possible.

Why do you need to merge the surfaces.

I want to FitSrf to get a clean model without dents.

Is it possible to generate the model in another way.

This is my basis:

NetworkSrf will not work the curves shown, even if the straight lines are the bottom are not included.

A requirement for the input curves for NetworkSrf:
All curves in one direction must cross all curves in the other direction and cannot cross each other.

The curves shown do not meet that requirement.

I’ll assume the bottom straight curves can be ignored.

A single surface with fits the curves shown will have to have either a polar singularity at the top, or a polar singularity at either end.

Possibility A:

  1. Create a point at the highest point of the “vertical” curves.
  2. Loft with either the Normal or Tight option using the horizontal curves and the top point.
    This results in a polar singularity at the top. .

Possibility B:

  • Split the bottom horizontal curve at either end.
  • Create a point at the splits.
  • Sweep2 using the split bottom curves as the rails, and the points and vertical as the sections.
    This results in a polar singularity at the either end.

Method to improve the results of A or B:

  • Patch command
  • Select both sets of curves as fit to.
  • Click on the “Select starting surface” option
  • Select the surface from method A or B as the starting surface.
  • Click on “Preserve Edges”
  • Enter a “Point spacing” which is a small fraction of the size of the object, such as 0.1 if the object is 10 long.
  • Enter

Using Patch will fit the surface as close as it can to the all of the input curves.
Optional - if the result of A or B is very dense then use Rebuild or FitSrf to simplify it before using as the starting surface.

Thanks a lot for your help.
Unfortunately it didn’t work well. But I found another way.

Know I have a new problem. Maybe you can help me a second time. :mit den Augen rollen:

At the first step I loft the ends with new lines. After that it was possible to merge the surfaces.

Now is there a new problem. When I FitSrf it the edge is not clean.