Reference Planes

Use a reference plane to sketch somewhere the model has no face. Open the Plane menu on the toolbar's Reference chip, click the kind you want, and answer what it asks for. P is the shortcut for the first of them, Plane at a distance.

A reference plane draws no material. It is a place to work: a support for a sketch, an axis source, a mirror plane, an input to a pattern.

The chip is on screen from an empty document onwards, painted plain grey while nothing is selected — like Sketch and Insert, it is a thing you make rather than a thing the selection unlocks. Clicking one of its tools always creates the step. Whatever you had selected is filled in, whatever you did not is left blank, the step reads grey and pending in the timeline, and its panel asks for each missing pick in turn: answer one and the next arms itself. Nothing is guessed, and a selection the tool cannot use no longer costs you a toast and no feature.

The five kinds, and what to select first

There is one tool per kind, so the kind is settled by the button you press rather than by what you were holding. Selecting first is still worth doing — it fills the picks in, and often finishes the plane in one click — but it is no longer what decides which plane you get.

A plane can stand on another plane. The first three kinds take a plane input rather than a raw face, so a reference plane can be offset, hinged or halved off another reference plane, or off one of the three world base planes. A stack of datums needs no body to measure from, which is how a row of shelves or a set of ribs gets laid out before the part exists. The one refusal left is timeline order: what you build on has to come earlier in the timeline than what you are building, and Kapy says so instead of creating a step that could never resolve.

Plane tangent to a cylinder is the one kind no datum can stand in for: it wraps a real cylindrical face. Its 0° is the direction from the axis out to that face's own centre, and it sits halfway along the face's run — so on a corner round the plane lands on the corner round, rather than somewhere out on the far side of a shaft that is not there.

The rules each kind enforces

Each kind refuses the input it cannot use, and says which:

• Plane at a distance needs a flat face, a reference plane or a base plane. A cylinder's side gets you Reference geometry requires a planar face here.
• Plane through 3 points needs three distinct points that are not in a line: Selected points are collinear — they do not define a plane.
• Plane between two needs the two to be parallel. Anything else gets Selected faces must be parallel for a midplane.
• Plane at an angle needs the edge to lie on the face, or run parallel to it — Edge must lie on or be parallel to the input face. An edge from the other side of the part cannot hinge anything.

A step still waiting for a pick is none of these. It is grey rather than red, it reads Waiting for an input to be picked, and the model downstream of it is left exactly as it was: a question, not a failure.

Those messages appear in English whatever language the editor is set to.

Distance, angle and Flip

Distance is in millimetres and takes a parameter or an expression like any other number in Kapy. A new plane starts 10 mm out, so it is visible the moment it exists. It can be negative, which puts the plane on the other side of the face. That is the same thing Flip does, and either is fine.

Angle is in degrees, positive one way and negative the other, and an angled plane starts at 45°. Neither field is clamped: type 900 mm and you get a plane 900 mm away, floating well clear of anything you modelled.

An angled plane also carries a gizmo: an arc handle drawn around the hinge, at the plane's origin. Drag it and the angle follows in whole degrees, or in 15° steps with Shift held. An angle driven by a parameter or an expression will not drag — that number has an owner, and the handle refuses to overwrite it.

Hiding one

A reference plane is drawn as big as whatever it was built from — a long thin face gives a long thin plane, a tangent plane on a shaft is as tall as the shaft's own run — and ruled with a faint grid patch so it reads as a surface instead of a wash of colour. Nothing geometric depends on that size: to every feature that consumes it, the plane is still infinite.

Even so, a plane in front of the part is a plane in the way. Turn Visible off in its panel, press V with that plane selected and nothing else — the same key that hides a body — or click the eye on its row in the References window. The plane stops being drawn while everything built on it keeps working.

A hidden plane cannot be clicked either. Turn it back on when you need to pick it again.

The plane you are in the middle of building is a case of its own: while its step is open and still missing a pick, it is drawn faint and skipped by every picker, so the faces and gizmo handles underneath it stay reachable.

See also

• Reference Axes and Points: the other two kinds of reference geometry
• Using References: what to do with them, and what breaks when you delete one
• Creating a Sketch: sketching on a plane once you have one