Arc and Ring
Draw arcs (open curved paths) and rings (closed donut/annulus shapes).
Arc and RingThe Arc tool draws an open curved contour defined by a center, radius, and start and end angles — designed for curved bed edges, semicircular patios, and flowing border transitions. It offers three construction modes you choose in the Construction Mode group at the top of the sidebar: Center + Angles (the default), Start + End + Radius, and 3-Point. The Ring tool draws a closed donut shape (annulus) defined by a center, outer radius, and inner radius — designed for tree surrounds, mulch rings, and circular planting borders. Both tools work bidirectionally: click on the canvas to populate the sidebar fields, or type values directly into the panel to position and size the shape. Click Apply in either panel to commit the shape as a new drawing entity.
Select the Arc or Ring tool
Choose the Arc or Ring tool. The tool sidebar opens on the right, showing the relevant parameter fields. The canvas cursor changes to a crosshair ready for your first click.
Draw an arc with Center + Angles (default)
In the default Center + Angles mode, the arc is defined by a center, radius, and a start and end angle. Click on the canvas or type into the sidebar to set the Center, Radius, Start Angle, and End Angle fields. The read-only Arc Length field updates automatically to reflect the geometry. For point-driven construction instead, switch to 3-Point mode (click start, a point on the curve, then end) or Start + End + Radius mode (click the two endpoints, then enter a radius).
Center + Angles mode is the easiest way to draw a precise semicircle: the arc sweeps from the start angle to the end angle around a fixed center, so you can lock to 90° or 180° increments by typing exact angle values.
Draw a ring from its center outward
With the Ring tool active, click once on the canvas to place the Center point. Move the cursor outward — the live preview shows both the outer and inner circles growing proportionally. Click a second time to set the Outer Radius and complete the ring. The default inner radius creates a visible band; adjust it immediately in the Inner Radius field.
Refine geometry in the sidebar panel
Type directly into any editable field — Center, Radius, Start Angle, End Angle, Outer Radius, or Inner Radius — and the canvas preview updates live as you type. Values are accepted in your project's current unit system (metric or imperial). Press Tab to move between fields, or click Apply to commit the shape.
Adjust ring band width using Inner Radius
The visible band of a ring is the area between its Outer Radius and Inner Radius. A larger inner radius produces a narrower band; setting inner radius to zero produces a filled circle. For a typical mulch ring around a tree, set the outer radius to match the desired mulch zone and inner radius to match the trunk clearance.
Name and apply the shape
Optionally enter a descriptive name in the Name field at the top of the panel — this label appears in the layers panel and cost schedule. When the shape looks correct in the canvas preview, click Apply to create the entity. The tool remains active so you can draw the next arc or ring immediately.
An arc is an open contour — it has no enclosed face and cannot be filled with a surface style. If you need a filled curved shape, use the Ring tool (closed donut), the Circle tool (filled disc), or close a Bezier curve instead. Arcs are best used for curved strokes, border lines, and edge decorations.
Rings make excellent tree surround guides. Set the outer radius to the drip-line radius and the inner radius to the trunk clearance, then assign a mulch surface style. The donut shape ensures the fill covers only the intended planting zone and leaves the trunk area open.
Keyboard Shortcuts
| Key | Action |
|---|---|
| Escape | Cancel current arc or ring |
Key Parameters
| Name | Default | Description |
|---|---|---|
| Center | Canvas click position | The XY position of the arc's geometric center (Center + Angles mode) or the ring's center. Can be clicked on canvas or typed in the panel. |
| Radius | Derived from canvas drag | The radius of the arc from its center to the curve. Must be greater than zero. |
| Start Angle | Derived from canvas click | The angle at which the arc begins, measured in degrees from the positive X-axis. Accepts values from -360° to 360°. |
| End Angle | Derived from canvas click | The angle at which the arc ends. The arc sweeps from Start Angle to End Angle in the counter-clockwise direction. |
| Arc Length | Auto-calculated | Derived field showing the total length of the arc curve, calculated from the radius and the angular span. Cannot be edited directly. |
| Outer Radius | Derived from canvas drag | The outer boundary radius of the ring. Must be greater than Inner Radius. |
| Inner Radius | Proportional to Outer Radius | The inner boundary radius of the ring (the hole). The band width equals Outer Radius minus Inner Radius. Setting to zero produces a full circle. |
Frequently Asked Questions
Why can't I fill my arc with a color or surface style?
An arc is an open contour — it has no enclosed face, so there is nothing to fill. If you need a filled curved shape, switch to the Ring tool for a donut band, the Circle tool for a full disc, or draw a closed Bezier curve for an organic enclosed shape.
What is the difference between the three arc drawing modes?
The arc tool offers three modes, selectable in the Construction Mode group at the top of the sidebar. Center + Angles (the default) defines the arc by its center and sweeps from a start angle to an end angle — best for degree-controlled arcs. 3-Point places start, mid, and end points directly on the curve. Start + End + Radius defines the two endpoints and then specifies the radius, useful when you know the chord length.
How do I make the ring band thinner or thicker?
Edit the Inner Radius field in the ring tool panel. The visible band width equals Outer Radius minus Inner Radius. Increasing the inner radius narrows the band; decreasing it widens the band. Setting inner radius to zero removes the hole entirely and produces a solid filled circle.
Can I edit the arc or ring after placing it?
Yes. Select the shape and edit its numeric values in the inspector, or use the Node Edit tool to drag the arc's endpoints and mid-handle to reshape the curve interactively.
Arc Length shows a value I didn't type — is that correct?
Yes. Arc Length is a read-only derived field calculated automatically from the radius and the angular span (end angle minus start angle, converted to radians). It updates live as you adjust any of the other arc parameters and cannot be edited directly.