grid — grid lines

grid X 0 6400 12800 19200
grid Y 0 5600 7600 13200

grid <axis> <coordinate mm> <coordinate mm> ... lists the coordinates of the grid lines on one axis. Nothing in this notation is written as a bare coordinate — position is always written in the language of the grid, so without a grid there is no way to write a region, a drawn line, or the position of an opening.

There are two axes, X and Y. X is positive to the east and Y is positive to the north; the vertical direction (z) is not an axis but belongs to level.

Grid lines are named for you

You write only coordinates; you do not name them. The coordinates of grid X become X1 X2 X3 … from west to east, and those of grid Y become Y1 Y2 Y3 … from south to north.

grid X 0 6400 12800 19200
#      X1 X2   X3    X4

A grid name is therefore an axis and an ordinal, not the gridline mark of a drawing (grid A, grid 1). If you want to carry the mark, write it as an attribute on a space or a boundary.

A name beginning with X is read on the X axis and one beginning with Y on the Y axis, so a reference never has to say which axis it means. Ordinals start at 1; there is no X0.

Declare it before you use it

A grid line has no effect on lines above it. A grid reference is resolved into a coordinate as its own line is read, so a grid placed further down arrives too late.

level L1 0 h:2400 slab:150
space /L1/a room X1..X2 Y1..Y2
grid X 0 3600
grid Y 0 4000

✖ gridlate.muro:line 2: Undefined grid line name: X1

This contrasts with boundary, which may forward-reference its spaces. A boundary joins two names; a grid reference points at a coordinate.

Once per axis

grid X and grid Y may each be declared once. When composing, that is once across all layers, and a second line is an error even with identical coordinates — the grid is one coordinate system for the whole building, not something later layers extend or replace.

✖ n5.muro:line 2: grid X is declared once (in the base layer when composing)

Rules for the coordinates

Rule	Error
The axis is X or Y	A grid axis is X or Y: Z
Two or more coordinates	grid takes two or more coordinates
Written in ascending order	grid coordinates are written in ascending order (equal values are rejected too)

Coordinates are numbers in mm and may be negative. Where the origin sits is your choice; the vertices of a polygon and the positions of columns are read in this same coordinate system.

Grid references — how position is spelled

A declared grid name is itself the word for a position.

Spelling	Meaning
X2	the coordinate of grid line X2
X2+600	600mm east of X2
Y3-150	150mm south of Y3
X1..X2+3200	a range (both ends are grid references)

An offset is an integer only. X2+600.5 is not readable as a grid name and is an error.

✖ g1.muro:line 4: Undefined grid line name: X2+600.5

Referring to a grid line that was never declared is an error too (Undefined grid line name: Y3). Ranges, regions, the endpoints of a drawn line, and the absolute position of an opening are all collected in positions and regions.

A grid line is not a drawn line

grid places coordinates; they have neither length nor endpoints. A grid line divides nothing by itself — what divides is a space's region and a boundary.

There is exactly one place where the grid produces form: a column stands at its intersections. A column's x: / y: restriction is written with grid names (x:X2,X3).

Canonical JSON

The grid is an array of coordinates per axis. Names follow from the ordinals, so they are not stored.

$ npx tsx src/cli.ts json lv.muro
  "grid": {
    "X": [
      0,
      6000
    ],
    "Y": [
      0,
      8000
    ]
  },

The smallest file

grid X 0 3600
grid Y 0 4000
level L1 0 h:2400 slab:150
space /L1/a room X1..X2 Y1..Y2

$ npx tsx src/cli.ts check min.muro
✔ Consistent — 1 space / 0 boundaries
  Structural consistency only — architectural validity is what koyu validate says, separately