ArcCurve

A curve formed from edges arranged in a circular arc or full circle.

ArcCurves are specialized Curve objects that represent arcs and circles in SketchUp. They track arc-specific geometry like the center point, radius, normal direction, and start/end angles. When you create a circle or arc with Operation.createCircle or Operation.createArc, the resulting edges automatically share an ArcCurve parent.

Full circles are marked with circular: true, while partial arcs have circular: false and use startAngle and endAngle to define their span.

Example

let model = await SketchUpApi.getActiveModel();

// Create a full circle and a partial arc.
await model.performOperation(op => {
  // Full circle: 24 segments, radius 50
  op.createCircle(
    model, [0, 0, 0], [0, 0, 1], 50, 24
  );

  // Partial arc: 45° to 135° (quarter arc)
  // Angles are in radians.
  const start = 45 * Math.PI / 180;
  const end = 135 * Math.PI / 180;
  op.createArc(
    model,
    [100, 0, 0], // center
    [1, 0, 0],   // xaxis
    [0, 0, 1],   // normal
    30,          // radius
    start, end,
    8            // segments
  );
}, 'Create circle and arc');

let curves = await model.entities.getCurves();
let circle = curves[0];
let arc = curves[1];

console.log(circle.circular, circle.radius);
// => true 50
console.log(circle.edges.length);
// => 24

console.log(arc.circular, arc.radius);
// => false 30
// Convert angles back to degrees
let toDeg = r => +(r * 180 / Math.PI).toFixed(0);
console.log(
  toDeg(arc.startAngle), toDeg(arc.endAngle)
);
// => 45 135

See

Since

SDK 2.23.0 Protocol 1.20.0

Properties

attributes

readonly attributes: Attributes

Custom attributes attached to this arc curve. Use attributes to store metadata or tags that survive file saves.

center

readonly center: Point3d

The center point of the arc or circle in model coordinates. All points on the arc lie at radius distance from this center.

circular

readonly circular: boolean

Whether this is a complete circle. True for 360-degree arcs, false for partial arcs.

edges

readonly edges: Edge[]

The edges that make up this arc curve, in sequential order. For a full circle, the first and last edges connect to form a closed loop.

endAngle

readonly endAngle: number

The angle in radians where the arc ends, measured from xAxis in the direction of normal × xAxis. For full circles, this is typically 2π.

id

readonly id: number

The persistent ID that uniquely identifies this arc curve.

isPolygon

readonly isPolygon: boolean

Whether this arc curve forms a closed polygon. True for full circles and closed arcs, false for open arcs.

normal

readonly normal: Vector3d

The normal vector perpendicular to the arc’s plane. Defines which direction is “up” for the arc. For a circle on the ground plane, this is typically [0, 0, 1] (Z-axis).

startAngle

readonly startAngle: number

The angle in radians where the arc starts, measured from xAxis. For full circles, this is typically 0.

type

readonly type: ArcCurve = EntityType.ArcCurve

vertices

readonly vertices: Vertex[]

The vertices at the junctions of this arc curve’s edges. For a full circle, the first and last vertices are identical.

xAxis

readonly xAxis: Vector3d

A vector from the center to the arc’s start point. Its length equals the arc’s radius. Combined with normal, it defines the arc’s local coordinate system.

Accessors

firstEdge

Get Signature

get firstEdge(): Edge

The first edge in this arc curve’s sequence. For full circles, this is an arbitrary starting edge. For partial arcs, it’s the edge at startAngle.

Returns

Edge

lastEdge

Get Signature

get lastEdge(): Edge

The last edge in this arc curve’s sequence. For full circles, this connects back to firstEdge. For partial arcs, it’s the edge ending at endAngle.

Returns

Edge

length

Get Signature

get length(): number

The total length of this arc curve, computed by summing the straight-line distances between edge vertices. For smoother arcs (more segments), this approaches the true arc length.

Returns

number

plane

Get Signature

get plane(): Plane

A plane containing this arc, defined by center and normal. Useful for projecting points onto the arc’s plane or testing coplanarity.

Returns

Plane

radius

Get Signature

get radius(): number

The arc’s radius — the distance from center to any point on the arc. Derived from xAxis.length.

Returns

number

sketchupId

Get Signature

get sketchupId(): SketchupId

JS API identifier for this arc curve. Pass it to API methods that accept a sketchupId.

Returns

SketchupId

typeName

Get Signature

get typeName(): string

Returns a named variant of the type field.

Since

SDK 2.35.0

Returns

string

yAxis

Get Signature

get yAxis(): Vector3d

A vector perpendicular to both xAxis and normal, completing the arc’s local coordinate system. Computed as normal × xAxis. Its length equals the arc’s radius.

Returns

Vector3d

Methods

refresh()

refresh(): Promise<ArcCurve>

Re-fetches this arc curve from SketchUp to get its current state. Because ArcCurve is a snapshot, it can become stale if the model changes (for example, if edges are deleted or the arc is modified). Call refresh() to get an up-to-date copy.

Returns

Promise<ArcCurve>

A new ArcCurve reflecting the current model state. Throws if the arc curve has been deleted.

Example

let model = await SketchUpApi.getActiveModel();
let curves = await model.entities.getCurves();
// Later, after the user makes changes...
if (curves.length > 0) {
  const fresh = await curves[0].refresh();
  console.log(fresh.edges.length);
}

toString()

toString(): string

Returns

string