Editing Sketch Geometry
Use Offset to make a parallel copy of a curve, Project to pull an edge of the model into the sketch, and X to mark a primitive as construction geometry that never becomes part of the shape. Reach for them once the sketch is drawn and the job is changing it: moving a point, thickening a wall, borrowing an edge, or turning a line into scaffolding.
Dragging
Drag any point or curve and the solver moves everything that has to move with it. What holds still is whatever you have constrained. Drag before you pin anything down to explore the shape: what moves is what you have not decided yet.
Delete removes the selection and takes its constraints with it. A constraint whose operands are gone has nothing left to hold.
Offset
Select a line, arc, circle or a connected chain, pick Offset, then move the cursor. The side you are on and how far you are decides the offset. Confirm and you get a parallel copy at that distance.
Offset the inner outline of a wall outward and you have both faces at a constant thickness, related rather than merely parallel-looking.
The copy is held to its source, not merely placed beside it. One number drives the whole chain — a single parameter behind a single chip, so there is one distance to edit and every piece follows it — and every smooth joint of the source gets a tangency between the two offset pieces, so dragging the original cannot turn a rounded corner into a kink. A sharp corner gets nothing extra: the shared point is the whole story there.
Two things the tool will not guess at. An arc whose offset radius has collapsed is dropped and its neighbours mitre, which is the ordinary "inset a rounded rectangle past its corner radius" case. And where the offsets of two neighbouring segments genuinely never meet, it refuses in words and names the two, rather than handing you a chain that is an offset of nothing.
Project
Use Project (P) to bring an edge or a vertex of the model into your sketch as linked construction geometry. Linked is the important word: it is not a copy you took once, it follows the edge it came from.
Reach for it when a sketch needs to line up with something already built: a hole centred on an existing boss, a rib that meets a wall exactly. Constrain to the projected geometry rather than eyeballing coordinates.
It takes any edge, and what the edge becomes is decided by its own geometry rather than by a list of what is allowed. A straight edge arrives as a line and a vertex as a point. A circular edge lying in the sketch plane comes in as a circle or an arc; seen edge-on it collapses to the segment it spans; at any angle in between it is a real ellipse, with its two axis lines. Anything else — a spline, a helix, the curve where two fused solids meet — arrives as a chain of fixed construction lines. When it cannot project something it names the reason rather than dropping it silently.
The tool stays armed across clicks, so the whole outline of a face is one trip to the toolbar rather than one per edge. Escape or another tool ends it, and clicking a source you already projected un-projects it.
Construction geometry
Select any primitive and press X to mark it as construction. It stays in the sketch, keeps taking part in constraints, and stops being part of the profile. A construction circle is never extruded, while the polygon inscribed in it still is.
Build scaffolding this way when you need it to survive: a centreline to mirror across, a circle a bolt pattern sits on, an axis to keep a drop pointing the right way. Several tools make their own, such as the gears' pitch and module lines, the ellipse's axes, and the water drop's circle and tip axis.
The face's own edges
Sketch on a model face and the face's straight edges and vertices appear in the sketch as read-only construction primitives. You did not put them there and you cannot move or delete them. Snap and constrain to them to line your drawing up with the face underneath it.
They re-extract after every rebuild, so a constraint anchored on one survives an edit that changes the face's shape.
See also
- Lines, Rectangles and Polygons: what each drawing tool leaves behind
- Regions and Profiles: why construction geometry never becomes a region
- Geometric Constraints: the relations you are editing around