Follow me with portion of circle

I can confirm this is the issue I’ve logged (SKOR-15235). I’ve been bothered by it myself for over a decade as a SketchUp user.

Follow Me doesn’t respect arc curves as curves, but treats them as a series of straight edges.

I too have used the workaround of rotating the rail half a segment. However this causes some other issues. With this approach the curve doesn’t really start where it should, which could look odd if you want to connect to a straight continuation of the same profile. The radius also gets applied from center to the segment midpoint, not center to vertex which is the convention when representing curves as a mesh. This can cause issues if you are taking measurements or further subdivide the surfaces.

The workaround I’ve come to use now is to extrude along the full circle, as Follow Me treats full circles as a special case and handles them correctly. Then I split that circle up into the arcs I need. It’s a few extra steps but it works.

2 Likes

As an occasional Rhino user I know that it is possible to combine mesh, surface and quad geometry in a single application. I wish SketchUp would follow suit to avoid these hassles due to segmented curves.

This is helpful. I get unpredictable results with follow me tool.

It is not quite clear what “correctly” would mean in this case. Have you noticed that your cross section is correct at the vertex , measured towards the center, but at the middle of a segment it is distorted? This is impossible to solve with this kind of geometry.

As you say, the cross-section inevitably varies as you sweep the imaginary cutting plane around the circle, because the geometry is composed of straight edges. Therefore, one must decide which cross-section is most important, for example where the sweep touches the vertices, or where the sweep touches the mid-points. Personally, I choose to focus on the vertex-based cross-section because that corresponds to the intended radii of the imagined circles or arcs.

Agreed. That’s where we should always think of the minimal angle section we will use to use to choose the best number of segments in a circle. I choose generaly 144 segments in a circle because I can make sections with 2,5 degres of accuracy. If 1 degre of accuracy is needed, then you must choose 360 segments for your circle.
This way, when you cut your full circulare shape made with the follow me tool, you alway cut it on a vetex ensuring that you still have a clean geometry.

Me, I had problem with a 280mm diameter shape made with follow me with a 144 segment circle. When I cut it, some faces are lost. It should be related to the tiny size of my segments, but I thought 280mm was large enough…

I do not fully understand the issue ( above my pay grade ) but I do not think there is a clear answer to the question due to the way SketchUp is coded,

I struggle to see this as a bug, seems like predictable behavior to me.
You can see from the z-fighting in this gif that the follow me quadrant has identical geometry to the circle with the exception of the ends, where they naturally finish perpendicular to the edge rather than at some unknowable angle. What should sketchup be using as the Finish Angle?
GIF 11-12-2021 1-58-19 PM

Ok to say that the end angle is predicable when we know how the follow me actually works. I still can see it as a bug because it is clearly not how we want it to work. As we are able to finally get what we want by cutting the whole circle shape, I really think that SU should embed this “finishing” operation in its programm

The start and finish angle that we expect is totally predicable. We just want it to match the radius

And if the path isn’t a simple arc?

I think this arc should have a center, so there’s still a radius. Even an elipse has a center. even en regular hexagon.
But you’re right with a non regular polygon, SU may fight to get the center…
SU then should be able to treeat differently regular polygon and non regular polygon.

Edit : I read “is an simple arc” instead of “isn’t a simple arc”

I’m not disagreeing with you, I remember when I was learning what a pain it was, but I still don’t see it as a bug, more like a feature request, or improvements to follow me, added options and such. Much like @eneroth3 's upright extruder solves that peculiar twist part of follow me.
But I’m just a user like most everyone else and it’s just an opinion, and we all know what opinions are…

Follow me has maybe not been created to achieve what many (many, many) users use it for.
Bug or not, there’s a long time problem that still remain unsolved. So indeed, that’s a feature request that could save so many hours to the users…
A new tool is maybe needed, or some option in the follow me, but we need something for sure.

I think such a tool would not be “follow me”. This would be another tool that somehow creates an extrusion based on a real arc, not a SketchUp arc. Since SU only uses edges the tool would have to decide how to construct the extrusion with edges to complete the arc. It is not “followme” which always follows a path of edges drawn by the user (not perfect though, as demonstrated by plugins that improve upon it).

Once I learned to use it, I never saw this as a problem, it is just part of SketchUp. For working with true arcs I use CADD.

Could you show us the geometry in SketchUp of such an extrusion, based on a true arc? I mean what would it look like? Segmented?

Right it would have to be segmented. It’s hypothetical. Being in SketchUp it would have to be made of edges, but the segments would have to be extrapolated based on the arc such that the ends of the extrusion are always perpendicular to the radius. Being in SU, it’s still an approximation–but not based on a drawn path like Followme.

The predictability of follow me makes it possible to create a path that will start and end Predictably.
Follow end

The convention for mesh models is that it’s the vertices that really count. The line segments are just approximations.

SketchUp already honors this in other places. If you select an Arc Curve, Entity Info shows the radius measured to the vertices and the arc length based on that radius. The various arc tools also measure radius to the vertices.

This topic was automatically closed after 186 days. New replies are no longer allowed.