Step by step

1. Pick the rectangular-base insertion point.
2. Set L and W for the rectangle.
3. Set transition height H.
4. Set round radius R2. E remains editable in Properties/Parameter Graph for the documented native contract.

Parameters

Autodesk Annex B defines L as rectangle length, W as rectangle width, H as transition height, R2 as upper-circle radius and E as eccentricity. The base point is the centre of the rectangle. AutoCAD Plant 3D™ 2026 currently accepts E but does not apply it to the native ROUNDRECT geometry, so Parter mirrors the centred runtime body while retaining E as an editable/exported parameter.

Placement

Placement is rectangle centre → L → W → H → R2. L/W grow equally about the rectangle centre and H follows the primitive axis. E is kept in Inspector/Parameter Graph rather than a mouse stage because Plant 3D™ 2026 currently ignores it geometrically.

Snapping

Designer exposes the bottom rectangle centre/corners/midpoints plus the actual Plant-runtime top circular centre/quadrants as semantic OSNAP targets.

Booleans

ROUNDRECT uses a dedicated closed rectangle-to-circle loft for Designer Union/Subtract/Intersect, using the same Plant 3D™ 2026 runtime-effective centred top circle.

Export

Exports directly as native ROUNDRECT(s, L, W, H, R2, E). E is still passed unchanged for Autodesk API/future-version compatibility even though Plant 3D™ 2026 currently ignores it in the body.

Keep in mind

• ROUNDRECT Anchor MIN/CENTRE/MAX uses the actual transformed Designer/runtime body bounds. In Plant 3D™ 2026 those bounds are centred in X because native E is currently ignored.
• In Parameter Graph, L/W are naturally centre-growing spans; H provides the normal ⇧ / ⇩ / ⇕ axial growth selector; R2 and E remain independent stored native parameters.

Keep building