Profiles

A profile is the tube’s cross-section: a wall between two boundaries. The inner boundary, the bore, is a first-class part of it.

ut_round(od = 12, wall = 2)                 // a round tube
ut_round(od = 16, wall = 2, split = [-30, 30])   // a C-section
ut_rod(d = 10)                              // solid, no bore
ut_profile(outer, inner)                    // any hollow section

Round tubes

ut_round(od = undef, id = undef, wall = undef, n = undef, a0 = 0, split = undef)

Give exactly two of od, id and wall; the third is derived. One or three is an error. (id, wall) is often the natural pair: the bore is the functional dimension and the wall is a multiple of extrusion width.

The outline is a polygon. Its point count follows $fa/$fs at the place ut_round is called, or set it with n. a0 rotates the first point.

A wall below 1.2 mm (about three perimeters on a 0.4 mm nozzle) is legal and warns when the run is checked: such a tube renders perfectly and can print as a hole.

id = 0 is an error. For a solid section use ut_rod(d).

Split tubes

split = [a, b] removes the angular range from a to b degrees, leaving a C-section. The angles are in the profile’s own frame, whose +X axis is the station’s roll reference. So split = [-30, 30] puts a 60° gap centred on the frame normal, and the frame policy decides where that points: frames.md.

A split section has an inner surface but no enclosed bore. It can be swept with ut_tube, and it cannot be a run in a network.

Any other hollow section

ut_profile(outer, inner = undef, meta = [])

outer and inner are lists of 2D points. Rectangular duct, D-sections and keyed bores all work, under three rules that ut_profile asserts:

Both loops are counter-clockwise (PROF-1). The inner loop too.
Both loops have the same number of points, and outer[i] and inner[i] sit at the same angle from the centre (PROF-2). Equal count is not enough. Sample both loops by angle, not by distance along the outline.
The inner loop lies inside the outer loop at every angle (PROF-1).

The codes are the ones the assert messages carry. PROF-3 is the thin-wall warning above.

A square bore in a round tube, sampled by angle:

function square_by_angle(h, n) = [for (k = [0 : n - 1])
    let(t = 360 * k / n, c = cos(t), s = sin(t)) h / max(abs(c), abs(s)) * [c, s]];

N = ut_fragments(7, 360);
prof = ut_profile(ut_ring(7, N), square_by_angle(4, N), [["od", 14]]);

meta is a list of [key, value] pairs. ut_round fills in od, id and wall. For your own sections, the tight-bend warning uses od when it is set and twice the reach otherwise; the thin-wall warning needs wall.

The angle rule exists because each end of a tube is capped by a strip between corresponding points, not by a general polygon triangulation. See ADR 0006.

Shell, bore and solid

One profile yields three regions, and the network assembler depends on being able to ask for each:

ut_solid_rgn(p)   // [outer, inner]   the finished wall
ut_shell_rgn(p)   // [outer]          the outside, filled
ut_bore_rgn(p)    // [inner]          the bore, as a solid

ut_tube(path, prof, part = "shell") or part = "bore" sweeps one of them alone. The bore uses the same path and the same frames as the wall, so a network can union every shell and then cut every bore (networks.md).

Reading a profile


`ut_prof_outer(p)`, `ut_prof_inner(p)`	the two loops
`ut_prof_od(p)`, `ut_prof_id(p)`, `ut_prof_wall(p)`	declared dimensions, `undef` if not in `meta`
`ut_prof_hollow(p)`	has an inner loop
`ut_prof_open(p)`	is a split section
`ut_prof_reach(p)`	farthest outer point from the centreline
`ut_bore_inradius(p)`	largest circle that fits inside the bore polygon

A polygon’s inscribed circle is smaller than the circle its points lie on, by cos(180/n). Use ut_bore_inradius for anything that must fit inside the bore, and ut_prof_reach for anything that must clear the outside.

Limits

One bore. Multi-lumen sections are not supported (#22).
One profile per run, constant along its length. Tapers and reducers are not supported (#20). Both mechanisms tried in design review did harm: scale baked into the station frame emitted a port at 0.6×, and a scalar multiplier on the region thinned a 1.6 mm wall to 0.96 mm. When variation arrives it will be separate od(u) and wall(u) functions of arclength.
ut_rod outlines must be star-shaped about their centroid, which any convex shape is. Its end caps are a fan from the centre.

The reasoning behind the two-loop representation of a split section is in ADR 0007.