Does Sketchup do actual circles yet or polygons still?


#1

I want to design some cylinder-based models for 3D printing later. I want the curves to be smooth and not faceted. I know many people have requested an actual-circle tool in the past but posts as late as 2015 suggest that it was at that time still doing simulated circles. Does anyone know the situation now? Thanks.


#2

SketchUp continues to represent circles internally as many-sided polygons with associated metadata for the original circle parameters. If you export a file as a 3D model, some of the exporters notice the metadata and export true circles instead of the polygons (e.g. the dwg exporter does so). Some kinds of edit operations can cause SketchUp to abandon the circle metadata, and when it is gone the circle will export as a polygon.


#3

Thanks. Have you any idea why they do this? Is it difficult to change? It looks like Autodesk CAD software does Real Circles™.

Do you know if recreating these objects in Sketchup would delete the circle metadata? There’s some push and pull operations and also some subtract operations.

It’s such a shame because I think Sketchup is brilliant but they poisoned the whole lot with this limitation. They say it’s good for 3D printing but this is a serious limitation :frowning: I’m trying to figure out AutoDesk 360 Fusion and it’s not nice!


#4

I think SketchUp handle circles this way because, at the core, SketchUp only uses two primitives for modeling: Edges (as in straight lines) and Faces. By storing the circle’s parameters in metadata instead as modeling primitives, the internals of the modeling (and, to the extent SketchUp does rendering) and rendering engines are vastly simplified. And since Faces - by definition - exist in a single plane, adding geometry where a “visual” face is bordered on a “side” by an actual circle (or part of one) in a different plane would result in an infinite number of hidden lines!

For most people, using “circles” with a sufficient number of sides suffices for on screen display - especially with smoothing and hiding of hidden geometry.


#5

A circle is a polygon with an infinite number of sides. You can get something close enough by making a circle with say 100 sides, the detail would be a lot higher than a 3D printer is capable or reproducing. If 100 isn’t enough, do 999 (that’s the upper limit). It’s pretty smooth.


#6

Circles when exported to, say, AutoCad DWG as a 3D model, do not depend on any metadata, they are just circles. But 3D shapes in SketchUp are all polyface objects, and to change that would probably require the program to be written anew from the ground up as a NURBS-based modeller. I am not against that, but I am afraid that it won’t happen soon. There are other applications with clunkier interfaces, like Rhinoceros, for those who need that kind of precision. Not free ones that I know of, however.

So the answer is that SketchUp does actual circles but actual balls or cylinders, no.

Anssi


#7

Totally off topic, but I just noticed your handle - @THX1138 - I love it!