ExtendDynamic

Natural

Lines, polylines, and polycurves with a line at the end to extend are extended by line.

Arcs and polycurves with arc at the end to extend are extended by same radius arc.

Other curves are extended smooth.

Arc

Makes an arc extension tangent to the original curve.

Arc options

Center

Extends a curve with an arc by picking the arc's center and endpoint.

Line

Makes a line extension tangent to the original curve.

Smooth

Makes a smooth curve extension curvature continuous with the original curve.

Yes — The extension is joined to the original curve, producing a single object (a polycurve). The original curve's geometry and parameterization are preserved exactly; the extension is added as an additional segment, so the point where they meet remains a segment boundary. This is useful when the original curve must not be altered.

No — The extension is created as a new, separate curve. The curve you picked is not modified at all. This is useful when you want the extension by itself, e.g., to trim it, assign it to a different layer, or use it as construction geometry.

Merge — The extension is merged into the curve itself rather than added as a segment. When the extension is the same kind of geometry as the curve end — a line extending a line, a same-radius arc extending an arc, or a smooth extension of a free-form curve — the result is a single, seamless curve span. This produces the cleanest result and is the default.