geometry

name	geometry
description	Use this skill for creating and manipulating geometry using ALLPLAN's geometry engine (NemAll_Python_Geometry module).

Overview

All geometry in ALLPLAN PythonParts is constructed using the NemAll_Python_Geometry module (aliased as AllplanGeo or AllplanGeometry):

import NemAll_Python_Geometry as AllplanGeo

Geometry objects are pure mathematical constructs — they define shapes in space but are not ALLPLAN model elements on their own. To place geometry into the model, wrap it in an AllplanElement (see the allplan-elements skill).

Core Principles

Units

• All coordinates and distances are in millimeters.
• All angles are in radians (use AllplanGeo.Angle.FromDeg() for degrees).

2D / 3D Duality

Most geometry types exist in both 2D and 3D variants (Point2D/Point3D, Line2D/Line3D, etc.). They share similar APIs but live in different coordinate spaces. A 3D object can often be constructed from its 2D counterpart (Z defaults to 0).

Two Solid Representations

ALLPLAN supports two types of volumetric solids:

Type	Class	Engine	Faces
Polyhedron	Polyhedron3D	ALLPLAN internal	Planar only
BRep	BRep3D	Parasolid	Curved (NURBS)

Prefer polyhedrons for performance. Use BRep when curved surfaces are required. Do not mix them in boolean operations — convert first.

When a BRep3D constructs a ModelElement3D, the element type is BRep3D_Volume_TypeUUID.
When a Polyhedron3D is used, the type is Volume3D_TypeUUID.
Never switch between them when modifying existing elements.

Transformation via Matrices

All spatial transformations (translate, rotate, scale, reflect) are expressed as Matrix3D (or Matrix2D). Apply with multiplication:

geometry *= matrix

Matrices compose via multiplication (order matters — not commutative).

Error Handling Pattern

Many geometry functions return an (error_code, result) tuple. Always check the error code before using the result.

err, polyhedron = AllplanGeo.CreatePolyhedron(solid)

Geometry Object Categories

Category	Examples	Characteristics
Primitives	Point2D/3D, Vector2D/3D, Angle	Building blocks, support arithmetic
Linear	Line, Arc, Polyline, Spline, Axis	Curves with length, no area
Areal	Polygon2D/3D, Plane3D	Closed/planar, have area
Volumetric	Polyhedron3D, BRep3D	Solids with volume

How-To Articles

Load these on demand based on the task:

• Geometry objects — Constructing geometry primitives and curves (Point, Vector, Angle, Line, Arc, Polyline, Polygon, Spline, Axis, AxisPlacement, Plane)
• Basic solids — Creating basic 3D solids (cuboid, cylinder, cone, sphere) as Polyhedron or BRep
• Extrusion — Extruding profiles vertically or along a vector
• Sweep — Sweeping profiles along a path or rails
• Revolve & Loft — Creating solids by revolving or lofting profiles
• Build from Scratch — Building BRep or Polyhedron from scratch (BRep3DBuilder, Polyhedron3DBuilder)
• Boolean Operations — Union, subtraction, and intersection of solids
• Intersections — Calculating geometric intersections (curve-curve, curve-plane, solid-solid, solid-plane, ray-solid)
• Transformations — Translation, rotation, scaling, reflection, projection, and composing transformations
• Fillet & Offset — Fillet edges/lines and offset curves/faces
• Measurement — Length, area, volume calculation, center of gravity, comparison, and polyhedron validation/repair
• Hidden Calculation — Projecting 3D geometry to 2D lines (visible/hidden edges)
• Tessellation — Converting BRep to Polyhedron via tessellation