oas-geometry

name	oas-geometry
description	Use when writing or debugging OAS geometry — points, polygons, line segments, arcs, circles, spirals, fillets, units, or coordinate conventions. Load before any geometry-heavy edit.

OAS Geometry

When to use

Use this skill whenever the task touches coordinates, curves, polygon validity, units, or angular conventions. This is the largest section of the spec, so load it early when you suspect a geometry bug (integer-mm violations, polygon not closing, arc winding wrong). If the work is about which entity owns the geometry (room vs. wall etc.), prefer oas-core or oas-layout.

Key types

• Point — { x, y } in integer mm (optionally z for railings on stairs)
• Polygon — ordered points array plus explicit "closed": true; closed: false is allowed for open paths (e.g. railings)
• LineSegment — straight edge from start to end
• Arc — circular arc with center, radius_mm, start_angle_deg, end_angle_deg
• Circle — full circle (center, radius_mm)
• Spiral / Fillet — specialty curves used for stairs and corners

Critical rules

1. No decimals in coordinates. Every x, y, z, radius, length is integer millimeters. The single exception is area_m2, which is a derived decimal value in square meters.
2. Polygons must declare "closed": true explicitly. A polygon without this flag is not closed by convention — don't rely on the last point matching the first.
3. Consistent winding. Point order must be uniformly clockwise or counterclockwise; do not mix. Positive rotation is counterclockwise.
4. Arc sweep is CCW from start_angle_deg to end_angle_deg. If you want a clockwise visual arc, swap start/end — do not negate angles.
5. Units are global. units.length is "mm" and units.angle is "deg" for the whole document; do not introduce per-entity unit overrides.

Full schema

See docs/geometry.md for the complete reference, including arc parameterization, spiral construction, and fillet rules.

Related skills

• oas-core and oas-layout — consumers of these geometric primitives
• oas-render — for how these primitives map onto screen coordinates (Y typically inverts)