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| description | Create a circular arc through three 3D points in TypeScript with Code3D. Learn point order, local coordinates, arc length and degenerate inputs. | |||||||||||||||||||
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Create a circular arc from a start point, a point on the arc and an end point. The three positions determine the circle, its plane and which arc to keep.
import {arc} from '@code3d/core';
export const circularArc = arc([-6, 0, 0], [0, 0, -6], [6, 0, 0]);
Select circularArc in the App to inspect the geometry.
Complete example: basic shapes.
function arc(start: Vec3, middle: Vec3, end: Vec3): EdgeModel;Import the function and any named types above from @code3d/core.
The same call works in the App and Node; Node initializes the kernel automatically.
| Parameter | Meaning |
|---|---|
start |
First endpoint |
middle |
A point the circular arc must pass through |
end |
Last endpoint |
All three parameters are required readonly [x, y, z] tuples of finite numbers.
The positions must define a nondegenerate circle: use three distinct,
non-collinear points. The middle point is on the curve; it is not a control handle
or the circle center. It need not be halfway along the arc.
The result is an EdgeModel<CurveElements> with a circular edge and two endpoint
vertices. middle does not create a third topology vertex. Coordinates remain in
the returned model's local XYZ frame; the model origin stays at zero.
The points may lie in any 3D plane, not only XZ.
The example creates the radius-6 semicircle through [0, 0, -6]. Its .length
is 6 * Math.PI, approximately 18.849556. Bounds run from [-6, 0, -6] to
[6, 0, 0], within kernel tolerance.
.start and .end reference the endpoints. .midpoint references the middle
of the arc's parameter interval; on a circle, it also bisects the arc length.
It equals the supplied middle only if that point was halfway along the arc.
.center is the bounding-box center, [0, 0, -3] in this example, not the circle
center or the point on the arc at half length.
Point order chooses the path from start through middle to end, so a major
arc is possible. Reversing start and end reverses traversal. An arc remains open;
use circle for a filled circular profile.
The constructor checks finite coordinates and rejects an all-identical point set. The modeling kernel rejects configurations that cannot define a circular arc, such as collinear points or repeated endpoints. Nearly coincident or nearly collinear inputs can also fail at kernel tolerance. There are no omitted-point or editing defaults.
The edge supports vertex/edge selection, .length, transforms, materials and
relations, but has no filled area or volume. Use it as a curved
sweep path with an appropriately positioned profile.
A curved arc cannot serve as a straight rotation axis.
See model values and local coordinates.