Distorted surfaces

Recently I seem to be getting this problem more frequently.

The shape began life as a rectangle (line) and using offset, gumball move and fillet curve, the resulting curves then created the surfaces using loft and PlanarSrf, the result then being joined together.

The issue appears after using the FilletEdge command, previously similar problems have happened after using Boolean Difference to create holes through the item.

I have scanned the forums, but not knowing what to call this, I have probably missed other posts.

Hello - please try DivideAlongCreases > SplitAtTangents=Yes on this object - does that sort it out?



thanks for the swift response. It more or less has sorted it, a small issue does remain.

Is it something I’m doing wrong?


Hi Chris, I don’t think you’re doing anything wrong - although I am puzzled by the vertical split in that funky-shading fillet surface… What happens if you `ShrinkTrimmedSrf?



that last command did sort it, I think I’m going to have to do some reading on those commands. Could you point me to a document that explains some of these functions.


If the help file doesn’t contain the information that you need then something is wrong with the help file and you should report that here.

For example: ShrinkTrimmedSrf


the help topics are working, but don’t give a lot of information, i.e. DivideAlongCrease has the following help for the options.

SplitAtTangents: Divides surfaces at tangent locations.
SplitAtKinks: Divides surfaces at kinks.

The thing is, I don’t know why I would want to do one rather than the other, or both.

But know I know of these two commands, I can use them as a starting point to search the McNeel WiKi for some more information.

cc: @margaret

Hi Chris,
Thanks for that feedback. In an ideal world you wouldn’t have to use the help file as a starting point to search other McNeel resources :slight_smile: Perhaps this one could be tuned up…

The help file entry for DivideAlongCreases starts by saying:

The DivideAlongCreases command divides a surface into separate parts at kinks or tangents.
Creased surfaces are divided into smooth pieces joined in a polysurfaces. Creased surfaces within a polysurface are divided and joined within that polysurface.

(Margaret, the hyperlinked word polysurfaces should be singular).

I suppose that for completeness sake, there should also be a link to an explanation of what tangents are. The explanation for kink has a rounded rectangle as an example. I suppose that this would rather be an example of a tangent. Also, the kink entry is about curves - the command can only be used on (poly-) surfaces.

I guess that the above would explain why you would use one rather than the other.
The initial question - “why would you want to use this command at all” - is not answered in that help entry. I hope that can be changed (but I understand that this would take some resources to get it right).


thanks for the reply.

I hope you don’t think that I’m complaining, working in Rhino is something I enjoy, mainly it just works.

I think I now have a feel for what will work and what will be a bit more playful. But every now and again, something comes along that I assume will be easy, yet proves not to be. The item that triggered this post was made from simple rectangles and some fillets, and yet two versions of it had a similar problem (which I now know how to fix).

While finding an instructional video for creating things in Rhino is easy, finding something on resolving issues is more of a challenge, if for no other reason than I’m not sure what the problem I’m having is actually called, so it’s difficult to do a search for it.

I often see commands appear in the list while typing in the command line (?) that I have no idea what they do, so I’m sure a whole raft of features lurk in Rhino that I would find useful.

Thanks again for your help.


Thanks for the feedback and suggestions. I will tune this up.

@cf53 The “Help” panel can kept always open with the “Auto-Update” option checked. Then when you run a command it will be available with information about the command and it’s options.

Hi, All,

It’s embarrassing, but explaining WHY you might use a command has been a problem since Rhino -1.0. We never really know why someone would want to use a particular command. Usually a new command comes out of a user having a problem that cannot be solved with the existing tools. Figuring out when it might be useful in other situations is almost impossible. The answers to these questions most often appear in training materials for creating specific object types, and, of course, by asking on this forum. :slight_smile:

The reason other commands appear when typing on the command line is so that you don’t have to type the whole command name out and to help you if you can’t remember the whole command name. What appears is based solely on spelling and has nothing at all to do with the function of the command.

Take a look at the Rhino Command Quick Reference topic. It makes pretty good bathroom reading. :wink:

1 Like



I am commonly experiencing similar issues with surfaces, particularly after Boolean operations. I have been trying to DivideAlongCreases, but this always seems to return with an error. I have used the UseExtrusions command to make sure geometry is Polysurfaces not Extrusions.

I also experience the same issue when Capping objects, particularly sweeps or lofts.

ShrinkTrimmedSrf also doesn’t seem to resolve this.

Has anyone come across this before / has a workaround?

I have attached some images of my workflow below…

Many thanks


Base Curves

Surface Errors

Post BooleanDifference


Swept Surface

Sweep Surface after Cap

Hi Charlie - can you post a Rhino file with the inputs to the Boolean operation? My guess is this is a render mesh problem that can be cleaned up by changing the setting in File > Settings > Mesh to ‘Smooth and slower’ or a custom setting (See https://wiki.mcneel.com/rhino/meshfaq)


I recall getting similar problem, not fixable
with display setting, when using loft with straight cross sections…

Hi Pascal

I have attached a different file with the same issue (deleted the original). Changing the mesh settings changes some, but not all of the settings.

I have identified that the problem seems to occur most frequently when extruding or sweeping along paths that include both straight and curved lines in the path. Breaking the path into multiple sections helps, but this isn’t always possible.

Many thanks!


Mesh Errors

Rhino 5:
Mesh Errors_5.3dm (844.9 KB)

Mesh Fast and Jagged:

Mesh Slow and Smooth:

Rhino 6:
Mesh Errors.3dm (790.6 KB)

Hello - run


on this object - start the command with no selection and set SplitAtTangents=Yes. That should sort out the shading.

Also, run the CreaseSplitting command and make sure splitting is enabled.


The problem is mainly given by the small front surface (see photo). You must use the _UntrimAll command> keep all the cuts, then “_InsertKnot”> automatic> both directions, 2 clicks on the mouse. Then cut the surface with the curve (I suggest to do it with the other surfaces too).
On the advice of Pascal, I always do this procedure when I have shading problems (sometimes it is enough _UntrimAll> keep all the cuts)


Mesh Errors_5.3dm (4.7 MB)