Curves

A curved piece is not defined by a length. It is defined by a radius and an arc, and its
length falls out of the two. The size vocabulary settles half of it, and this page settles the other half.

Doing rather than reading?

The turn goes in the name like any other size word. The radius does not.
SM_Kit_AbandonedTavern_01_Wall_Tower_QuarterTurn_01 is the whole convention.

First: does this kit need curved pieces at all?

Usually not, and it is worth deciding before naming anything.

One round tower is a Prop. It snaps to nothing and tiles against nothing, so the category
ladder already says so. A prop can be modelled at whatever radius the building wants, with no vocabulary, no checks and no family to keep in step.
→ Asset Rules (Generated) > The decision ladder

Curved kit pieces earn their place when the same curve recurs: a tower that exists at two
storey heights, an apse that also appears as a bay window, a bastion repeated round a wall. The cheapest curve convention is the one you never use.

The turn is a word, like every other size

curves.svg

A curved piece is a fraction of a circle rather than of the module, through the same parser
every other size word uses:

SM_Kit_AbandonedTavern_01_Wall_Tower_QuarterTurn_01
SM_Kit_AbandonedTavern_01_Wall_Tower_EighthTurn_01

Turn words, worked out

A different list, because the legal fractions depend on what they are a fraction of. Every one is a unit fraction: N pieces of a 1/N turn close a circle for any N, and nothing else closes at all.

Word Fraction Degrees Pieces to close a circle
FullTurn 1/1 360 1
HalfTurn 1/2 180 2
ThirdTurn 1/3 120 3
QuarterTurn 1/4 90 4
SixthTurn 1/6 60 6
EighthTurn 1/8 45 8
TwelfthTurn 1/12 30 12
SixteenthTurn 1/16 22.5 16

The list is unit fractions only, and that is the whole constraint. N pieces of a 1/N turn
close a circle exactly, for any N. A SixteenthTurn is 22.5°, and sixteen of them are perfect.
Nothing else closes at all: ThreeQuarterTurn is a legal shape, and four of them make three circles rather than one ring.

The legal fractions depend on what they are a fraction of

Third is excluded from a length because a third of a 4 m segment is 1.333 m and lands on
nothing. A third of a turn is 120°, three of them close a circle, and there is nothing wrong
with it. ThreeQuarter is the other way round: fine on a length, never on a turn.

Both spellings parse, so the add-on asks separately and reports the one its axis does not allow.

The radius is a family, not a number

Wall_R4_QuarterTurn looks more helpful and is the same trap as Wall_4m.
→ Modular 3D Assets > Saying how big it is

So the name carries the family instead. The family is a word somebody chose, whereas a radius is a measurement:

SM_Kit_AbandonedTavern_01_Wall_Tower_QuarterTurn_01
SM_Kit_AbandonedTavern_01_Wall_Apse_QuarterTurn_01

MSH020 then checks that every piece of one family agrees about a radius, by agreement rather than against a number: the majority radius is the kit's, the piece that differs is named, and a family with one piece in it is never asked. Wall_Tower_QuarterTurn and Wall_Tower_EighthTurn are one family at two arcs, which is the point of having one.

curves

Key Value
appliesToCategories Kit
measureFrom vertices
wholeTurn 360
turnTolerance 1
radiusTolerance 0.05
minimumTurn 1

Convex and concave are two pieces, not one flipped

Only one face of a wall is detailed. A tower seen from outside and an apse seen from inside are different meshes at the same radius and the same arc. The family word carries that difference too, which is one more reason for it to be a word.

What a turn changes, and what it does not

Curvature is not a fifteenth class. A curved wall is still a wall: it carries a storey, it has a wall plane, and its origin is the bottom-left of its leading edge. A curved trim is still trim, which projects. What a turn changes is four things the class would otherwise decide alone:

Straight Curved
MSH015 grid footprint fills its cell exempt. An arc has no axis-aligned cell, the same exemption roof takes
Tiling axis X none. It tiles by rotation, which no list of axes can say
MSH013 connecting faces the two X planes the two ends of the arc: radial planes through the centre
Assembly translate by the module rotate by the turn about the arc centre

The pivot is unchanged, so a curved run snaps to a straight one with no special case.

It is read off the name, not off a setting

The pivot class has to be declared because nothing in a mesh says whether it is a wall or a floor. A turn is different: the word is already in the name where a level designer reads it, and the arc is already in the geometry where it can be measured. A second declaration would be a third place for the same fact to disagree.

What the add-on does with it

None of this needs a setting. The turn word in the name is the only input.
New Kit Piece builds it Pick Turn as the axis and the wizard spins an arc instead of a box: named, pivoted, unwrapped and at the radius the rest of the family already uses. Start curved pieces here rather than modelling first and naming afterwards, so the name and the geometry agree from the start.
The viewport draws its circle The Module Envelope overlay has no cell to draw round an arc, so it draws the whole circle the piece is part of, the radius, and the two ends. It turns red when the name and the arc disagree.
The assembly preview turns Lay a run of a curved piece and it is laid round its own centre, as many as close the circle, which for an EighthTurn is eight. A turn that closes nothing lays one lap and stops, so you see it fail to meet.
The tile test turns too A curved piece's neighbours are the same piece rotated one turn each way about its centre, which is where they are in a tower. No corner ghost: a corner is where a straight run turns, and this one is already turning.
The Kit panel does the arithmetic How far it runs along its middle, how many close a circle, and (when the name is wrong) which turn it actually is. "This is wrong" and "this is an EighthTurn" are the same finding and a different amount of work.
Help › Which Size?

The whole vocabulary worked out against this kit's own module: what each fraction is in metres, which axis each word claims, what each turn is in degrees and how many of it close a circle. Also on the Kit panel and in the New Kit Piece dialog.

A FullTurn (a closed ring) is measured correctly too, and the flat-face check (MSH013) looks at the two ends of the arc rather than at the piece's bounding box, so a clean curved piece does not get false bevel warnings.

What the check can and cannot see

It measures a claim, and it does not go hunting

MSH020 is asked only about a piece whose name carries a turn word. It says nothing at all about a curved piece that carries none, in the same way MSH017 declines to measure a gable.
→ Roofs > The gable is the piece that will bite you

Geometry alone can't reliably tell whether a piece is curved, which is why the name has to say so. If a curved piece carries no turn word, nothing checks its radius or its turn.

  • Model at the studio facet. The arc measurement is most reliable on pieces built with the facet count New Kit Piece uses. Very coarse arcs (three or four segments) are harder to read.
  • A straight wall named as a turn is reported. Naming a straight piece HalfTurn does not slip through.
  • If a finding looks wrong, check the piece in the viewport first. The overlay draws the circle the add-on thinks the piece belongs to, which usually shows what went wrong.

See also