Circle, Arc and Curve in SketchUp

circles in sketchup

SketchUp models geometry is based on an edge. Any shape or surface is made of edges. Next position on the basic SketchUp entities list is an circle. In this text you can learn all details that has something to do with arcs and circles.

In this article you can learn:

  1. Circle sides in Sketchup
  2. How to draw a circle in Sketchup?
  3. How to check the diameter and segment amount?
  4. Can I edit a circle?
  5. Difference between circle and arc
  6. What is curve geometry?
  7. Create an arc between two edges
  8. Round many edges corners at once

Why SketchUp draw circles using bunch of edges?

circles segments

SketchUp uses Polygonal Modeling to approximating their surfaces. It means every surface is described by set of edges. The same situation is with circle, so every of them is draw with edges.
Most practical information is that you need to decide whenever you need detailed and smooth shapes with big number of circle segments or any simplicity which helps to make model easier to work with is more important so you prefer to set small circle sides. In other words you can use small circle sides parameter and get not so natural representation of curved shapes but your model will be "light" and will work smoothly or you can set big value of segments to make the model realistic but working slower.
It's your choice and you need to know about that decision to make at the beginning of the design process.

How to draw a circle in Sketchup?

To create circle in SketchUp:

  1. Use proper tool from Drawing toolbar or just press "c" button (it is default circle shortcut key).
    circle tool from drawing toolbar

  2. Check circle sides (segments). To change it simply use numeric keys.
    circle sides

  3. Click mouse button to choose circle middle point.
    circle center

  4. Set circle radius with mouse cursor or use numeric keys to set exact value.
    circle radius

  5. Done!
    circle done

How to check the diameter and segment amount?

When you select the circle and open context menu with right mouse button, you can open Entity Info tray window.

circle entity info

You will find there the most important info about the circle. Radius and segments.

circle entity info tray

Can I edit the circle?

YES. There is a easy way to change circle diameter and it's sides (segments). Just open Entity Info window, as described above, and you can change radius or segments as you need. When you change numeric value in the window and press enter, the circle is redraw with new radius:

circle entity info new radius

You can also set new segments for the circle eg. 6 sides:

circle entity info 6 segments
Or change it to 360 with no time:

circle entity info 360 segments

Difference between circle and arc

When there is a need to draw not full circle you can use Arc tool.

arc tool

Basic functionalities works same as circle drawing but there is an additional parameter which is an arc angle and a start point. After you set arc center point and it's start point you need to indicate an arc angle as well. Same as before you can use also numeric keys to set precise value.

arc angle

The difference between those two geometric entities is that a Circle is an full Arc with 360° angle. When you open Entity Info tray window you see proper entity type and same as with circle you can check and change basic parameters like radius and segment amount.

arc info

What is curve geometry?

Any circle or arc can be transformed to a group of edges. For example if you select circle edge and open context menu you find there Explode function. When you explode circle shape every segment of the circle is a separate edge.

exploded circle edges

If you select few edges which are connected to each other you can use context menu: Weld function. As a result you get a Curve. In other words the curve geometry is a group of connected edges which are not a full circle or an arc.

exploded circle edges

Create an arc between two edges

If you need create an arc between two edges you can use SketchUp native tools for that. Because you read this article you know all the needed information to draw a smooth arc on the corner of edges. However, there is a simple plugin that will help you a lot with that. Check this SketchUp round edges extension.

To draw and arc between edges just do a few simple steps:

  1. select two edges
  2. run plugin (launch setting window)
  3. set radius and circle segmentation
  4. done!
round edges corners extension
edges rounded

Round many edges corners at once

But what can we do if we have many corners to be rounded?
There is a solution for that!

Use Round edges corners 2 SketchUp plugin.

It has a few advantages against the previous one:

  1. you can set arc radius with slider or use precise value
  2. there is an live view of the arcs - moving slider changes arcs online
  3. you can select many corners to round at once
round edges corners 2 extension
edges rounded with second version