Regions and Profiles

Use regions to tell an extrude what to build. A region is a closed area that the lines and curves of a sketch enclose, and you pick the ones you want by clicking inside them. Knowing what counts as a region explains most of the moments where an extrude refuses to do what you expected.

What makes a region

Every time the sketch solves, the editor looks again for closed areas. It leaves construction geometry out of the search, cuts each remaining curve wherever another curve crosses it, and takes every closed area it finds as a region.

Keep these in mind while you draw:

• Only closed areas count. An open chain of lines encloses nothing and offers nothing to extrude. A gap of a hundredth of a millimetre is still a gap.
• Crossings split. Two overlapping rectangles are not two regions but several, one for each area the outlines cut out of each other. That is usually what you want, and occasionally a surprise.
• Construction geometry is invisible here. A construction circle never contributes a boundary, so it is safe to use as scaffolding.

Holes come for free

A region inside another region is a hole. Draw a rectangle, draw a circle inside it, and you get two regions: the ring between them, and the disc. Extrude the ring and you have a plate with a hole, with no boolean and no second feature.

Choosing which ones

An extrude consumes regions, and you pick them by clicking. Two regions selected together come out as one body. What makes a hole is the region you leave out. Select the outer ring and not the disc inside it, and the disc is cut away. Select both and you get a solid plate, because a selected region is always filled, never a hole.

There is also a switch for "all of them". Turn all regions on and the feature re-derives the region set from the sketch every time it rebuilds. Add a hole to the sketch later and the extrude picks it up on its own, rather than needing you to edit the feature and re-pick.

Turn it on for a sketch you expect to grow, such as a pattern of holes or a plate that gains a slot. Leave it off when you deliberately want a region left out.

Region identity across edits

A region keeps its identity as long as the primitives forming its boundary survive. That is what lets an extrude keep pointing at the right area when you move a line or change a dimension. Edit the original line rather than deleting it and drawing a replacement.

A redrawn boundary does not usually break the feature. The match falls back to finding the region that still contains the same interior point, which is a guess rather than a certainty, and it holds until the area moves far enough that the point falls outside. Then the feature loses its region for good.

Bounded sketches

A sketch on a model face can be clipped to that face's outline, so anything you draw past the edge simply does not exist. Regions are computed after the clip, so "cover this face in a grid of holes" is a single sketch rather than an exercise in trimming. See Creating a Sketch for when a sketch is bounded and when it is not.

See also

• Extrude and Cut: the feature that consumes them
• Editing Sketch Geometry: construction geometry, which never counts
• How the Solver Works: regions are re-found after every solve