Shaded view strange

Does anyone reconize this? I found some explanations that cited the origin, but I don’t quite understand that in regards to this. The surfaces indicated by the arrows are sucking in rather than holding to the surface edges.

Shading Issue.3dm (317.0 KB)


you’ll encounter such shading problems often when a surface is made of a 100% linear part and a curved one, the mesher will have a hard time to create a clean mesh using the coarse default settings. To see what causes the visual artifact, use _ShowRenderMesh. One way to get rid of it, is to change the mesh settings of this part in properties, eg. using these seems to cure it:

A better way is to avoid such constellations and split the surfaces along isopharm (_Shrink=Yes), at the point (the knot) where the linear part marches upon the curved one. (marked with red curves in the file below). Modeling this way is often easier and linear surfaces can be built with degree 1 in linear direction, which means more accuracy too.

Shading Issue_cg.3dm (413.3 KB)


Hi Clement.,

Thanks for the help. I took a look at the render meshes as per your advice. So this issue is not due to a modeling error but rather the nature of the render mesh function in such circumstances. (Yes?)

I dont know what the “shrink+yes” is relevent to. Is that referring to a trimmed surface as in _shrinktrimmedsurface?

I used a two rail sweep to create all surfaces and then matched the upper to the lower for good measure. Afterwards all was joined, mirrored, connected with lofted surfaces and made solid. As I understand it, you simply split surfaces at the joints of complex and simple ( or create them that way) and then join into a solid when needed.

Also, when you say “March” did you mean match?

After making the split I get a clean mesh but it looks unneccesarlily dense.


Is that result of the complexity of the arcs used to create the surface?

Yes. Some geometry can get tricky to mesh and you can give the mesher a hand by changing geometry slightly.

Yes, try to eg. extrude an arc then use _Split _Isocurve without the _Shrink option. Then turn _PointsOn for one half. The underlying surface is still there. Using _Split=Yes this is not the case. It basically has the same effect as shrinking it afterwards.


Check in properties if you still use the Custom Mesh settings for that part.


Okay, very good! But then there’s this confusing thing likely due to my non-experience with mesh aspects - that is as you can see in the image the mesh and the selected surface. I’m in the Mac version of this, and I don’t see a means to turn off the mesh. That’s whats showing just like isocurves I think.

What happens if you select the object and run _HideRenderMesh ?

btw. quickly turning on/off _FlatShade is also a good way to find out if a display artifact is just caused by the rendermesh of a nurbs surface…


Well then …

so after I mirror the lovely new surface and reconnect all the parts into a solid, I get the little mess below.

Apprently the same thing happens on flat surfaves that meet at the same type of edges.

_hiderendermess works.

I suppose if a mesh looks like poop, then it’s probably because the line work is of the same quality.

good :wink: It is just an attribute, if you have one object which has the attribute enabled and join it to another object which doesn`t have it enabled, the attribute is transferred. Similar like an object cannot have two colors, eg. try joining a red curve to a blue one, the first selected object color wins.

You can mesh perfect nurbs geometry badly too. It is just important to understand that whenever you´re evaluating your nurbs geometry, you´re seeing a render- or display-mesh which is just an approximation.