The BRL-CAD Object Catalog: A Visual Reference to Every Object Type

Everything in a .g database is an object with a unique name. There are three broad families:

Objects may also carry arbitrary attributes (name/value pairs), which is how modern BRL-CAD records region IDs, material assignments, authorship, and any user-defined metadata.

The ARB ("ARBitrary" polyhedron) is a convex solid defined by up to eight corner points. The family members arb4, arb5, arb6, arb7, and arb8 differ only in how many distinct vertices they use; internally all are stored as eight points (coincident points collapse faces). ARBs are the most common way to model boxes, wedges, ramps, and tetrahedra.

Recipe (an axis-aligned 6x4x3 box):

Shortcuts exist for common cases: arb4 (4 points, a tetrahedron), arb5 (5 points, a pyramid), arb6 (6 points, a triangular prism), arb7 (7 points). The generic Boolean-friendly box shortcuts rpp, box, and raw are TGC-free ways to type boxes and are described with the TGC family below.

Where arb8 is defined by its corners, arbn is defined by its faces: an arbitrary number of half-space planes whose common interior is the solid. Each plane is given as an outward-pointing unit normal and a signed distance from the origin. This is the natural way to model faceted shapes with more than eight faces — prisms, cut gemstones, chamfered blocks.

Recipe (a hexagonal prism — six side planes plus a top and bottom):

A half is an infinite solid: all of space on one side of a single plane. By itself it is unbounded, so it is almost always used in a Boolean expression — subtract a half-space to slice a flat face onto another solid, or intersect to keep only one side.

Recipe (the plane z = 0, solid below it):

The general ellipsoid is defined by a center V and three mutually perpendicular semi-axis vectors A, B, and C. Their lengths set the three radii and their directions orient the solid, so a single ell covers everything from a perfect sphere to a flattened disc or a slender spike.

Recipe (a tri-axial ellipsoid, radii 5 x 3 x 2):

Two convenient alternate forms create the same ell primitive:

The sphere is the ell special case where all three axes are equal, exposed as its own type for convenience: just a center and a radius.

Recipe:

The superellipsoid generalizes the ellipsoid with two shape exponents, n (north-south) and e (east-west). With n = e = 1 it is an ordinary ellipsoid; larger exponents square it off toward a rounded box, and smaller exponents pinch it toward an octahedral or star-like form. It is invaluable for organic-yet-controllable shapes.

Recipe (a rounded box):

The TGC is BRL-CAD’s most versatile analytic solid. It is a generalized cone: an elliptical base (axes A, B) at vertex V, connected by a ruled surface to a second, independently scaled ellipse (axes c*A, d*B) at the far end of the height vector H. By choosing the top scale factors and axis directions you obtain cylinders, cones, frusta, and skewed or elliptical variants — all as one primitive.

Recipe (a cylinder skewed and tapered into a funnel):

The TGC has a rich set of shortcuts for common cases:

The everyday cylinder: a circular base of radius r at V, extruded along H. It is the tgc case A ⟂ B ⟂ H, |A| = |B| = r, c = d = 1.

Recipe:

A circular cone frustum: base radius r_base at V, top radius r_top at V + H. Set r_top = 0 for a sharp cone.

Recipe:

A cylinder with a constant elliptical cross-section, given by two base axes A and B extruded unchanged along H.

Recipe:

A circular torus: a tube of radius r2 whose center sweeps a circle of radius r1 in the plane whose normal is N, centered at V.

Recipe:

Like tor, but the swept cross-section is an ellipse rather than a circle. The ellipse’s semi-major axis is the vector C (which may tilt out of the plane) and its semi-minor axis has length d.

Recipe:

A prism whose cross-section is a parabola. The parabola opens along the breadth vector B, has half-width r at its mouth, and is extruded along the height vector H.

Recipe:

The hyperbolic analogue of rpc: the cross-section is one branch of a hyperbola. The extra parameter c is the distance from the curve’s vertex to the point where its asymptotes cross — small c gives a sharp cusp, large c approaches a straight-walled trough.

Recipe:

A solid paraboloid "dish" or "bullet": an elliptical base (semi-axes r1 = |A| and r2 = |B|) at V that closes to a single point at the tip V + H.

Recipe:

A flaring, horn-like solid: an elliptical base at V whose wall follows a hyperbola as it rises along H. As with rhc, c controls how sharply the wall flares (small c) or straightens toward a cone (large c).

Recipe:

The classic "cooling tower" shape: a surface of revolution (or elliptical generalization) that pinches to a narrow waist in the middle and flares at both ends. The neck-to-base ratio c sets how pronounced the pinch is.

Recipe:

A "particle" is a rounded body swept between two spheres: a sphere of radius r_v at V and a sphere of radius r_h at V + H, joined by a smooth conical skin. Equal radii give a capsule (rounded cylinder); a zero height gives a sphere; unequal radii give a rounded, tear-drop cone.

Recipe:

A whimsical but fully analytic heart solid, handy for teaching and for ornamental modeling. It is centered at V, oriented by three direction vectors (xdir, ydir, zdir), and shaped by a single distance-to-cusps parameter d that controls how pointed the bottom and how full the lobes are.

Recipe:

A metaball is defined not by a fixed boundary but by a field: each control point emits a field that falls off with distance, and the surface is the iso-contour where the summed field equals a threshold. Nearby points merge into smooth, organic blobs; distant points stay separate. Metaballs excel at fluids, soft bodies, and fillet-like blends.

Recipe (three points blended at a threshold of 1.0):

The BoT ("Bag of Triangles") is BRL-CAD’s triangle-mesh primitive and the most common target for imported and tessellated geometry. It stores a list of vertices and a list of triangles (index triples). A mode selects how the triangles are interpreted: a thin surface, the boundary of a solid, or a FASTGEN plate (each facet given a thickness).

Recipe (an octahedron — 6 vertices, 8 solid faces):

The ARS builds a surface from a stack of waterline curves — horizontal cross-sections, each with the same number of points — much as a ship’s hull is lofted from station lines. The system connects consecutive waterlines into a closed triangulated surface.

Recipe form:

The NMG is a full boundary representation built from an explicit topological hierarchy — shells, faces, loops, edges, and vertices — with rigorous adjacency information. It supports both planar and (via the same framework) non-planar faces and is the substrate BRL-CAD uses for many Boolean and tessellation operations. NMGs are typically produced by facetize or by import/conversion rather than typed by hand.

The BREP stores a solid as a set of trimmed NURBS (Non-Uniform Rational B-Spline) surfaces, using the OpenNURBS toolkit. This is the representation used for high-fidelity CAD interchange (e.g. STEP and IGES) where exact curved surfaces matter.

For backward compatibility BRL-CAD also recognizes two older explicit types:

A sketch defines a planar drawing: a set of 2D vertices connected by segments (lines, circular arcs, Bezier and NURB curves), embedded in 3D by an origin V and two in-plane axis vectors A and B. A sketch is not itself a solid; it is the input to extrude and revolve.

Because sketches are structured, they are created with the put command (or interactively in the Sketch editor) rather than with in:

extrude sweeps a sketch linearly along a vector H to produce a solid. The sketch’s local axes are re-mapped by the A and B vectors, allowing the extrusion to be scaled or sheared as well as translated.

Recipe:

revolve sweeps a sketch about an axis through a given angle, producing turned shapes such as bottles, wheels, and lathe parts. A full 360-degree angle yields a closed body of revolution; a smaller angle yields a partial wedge.

Recipe (a 300-degree sweep of a profile):

A DSP raises a rectangular grid of elevation samples over the XY plane, forming a height-field surface — ideal for terrain. Cell spacing and a vertical scale map the raw samples into model space; optional normal interpolation smooths the facets.

Recipe:

An EBM turns a 2D black-and-white image into 3D: every "on" pixel becomes a unit cell extruded to a common height along +Z. It is a fast way to build stencils, text, logos, and other complex outlines from an image.

Recipe:

A VOL is a full 3D grid of cells; cells whose stored value falls between a low and high threshold are solid. This represents true volumetric data — CT/MRI scans, simulation grids, 3D masks.

Recipe:

The HF is an older height-field primitive superseded by dsp. It reads heights from a data file with an optional control file and a cv-style format descriptor, then positions the field with an origin and two in-plane direction vectors. New models should prefer dsp; hf remains for reading legacy data.

The pipe primitive sweeps a (possibly hollow) circular cross-section along a poly-line of control points, rounding the corners with per-point bend radii. Each point independently sets an inner and outer diameter, so a single pipe can taper or transition between solid rod and hollow tube along its length.

Recipe (an elbow):

The PNTS primitive stores a set of points — typically from a 3D scan. Points may be bare, or carry per-point color, surface normal, and size, and can be rendered as small spheres for visualization.

Recipe (five plain points):

Datums provide geometric references — a point, an infinite line, or an unoriented plane — to which other geometry can be constrained or measured, following the ASME Y14.5 notion of datum reference frames.

Recipe (a datum plane through the origin with +Z normal):

A grip is a pseudo-solid "handle": a center point, a direction, and a magnitude, used as a manipulation or reference marker. It displays as a marker but has no ray-traceable surface.

Recipe:

A joint marks an articulation between two referenced paths in the model tree — the scaffolding for kinematics and assembly articulation. It stores a location, two vectors defining the joint’s motion frame, a joint value, and the two reference paths it connects.

Annotations place text labels in the scene, optionally tied to a point of interest by a leader. They are used to dimension and document a model directly in 3D. Legacy annotations keep their two-dimensional offsets in screen space. Model-space annotations instead store two basis vectors that embed their leaders, dimensions, symbols, and text in a plane in the model.

Annotation text is UTF-8. BRL-CAD loads scalable TrueType fonts at runtime and plots their glyph outlines, preserving the annotation plane and text rotation. OSIFont is the default because its technical lettering and engineering symbols are suited to dimensioning and PMI. A segment style may select a font by an installed filename, by a name whose .ttf suffix is implied, or by a path. If that font cannot be used, plotting tries OSIFont and then the built-in stroke font. The font file remains an installed data file; it is not compiled into BRL-CAD.

Enhanced annotations may also preserve a semantic role for each segment, such as text, leader, extension line, dimension line, arrowhead, or symbol. Line pattern, width, color, font, and symbol metadata can accompany those roles. Importers can therefore retain PMI meaning separately from the plotted geometry even when a display backend does not implement every style property.

Recipe:

A combination is an interior node of the model tree: a Boolean expression over other objects, built with union (u), difference (-), and intersection (+). Combinations are what make BRL-CAD a CSG modeler — you sculpt complex parts by adding, cutting, and intersecting primitives.

Combinations are built with dedicated commands rather than in:

A submodel references a treetop in another .g file (or the current one) and instances it as a single primitive, with its own space-partitioning method. This allows very large assemblies to be composed from reusable, independently prepared model files.

Recipe:

The CLINE is a FASTGEN-compatibility primitive representing a "connected line" structural element — a rod (or, with a wall thickness, a tube) of given radius along a segment. It is normally created when importing FASTGEN models.

The in command does not build a cline; create one directly with put:

A binunif stores a raw, uniformly typed array (floats, doubles, or signed and unsigned 8/16/32/64-bit integers) directly inside the database. It is the in-database home for the sample data that dsp, ebm, and vol can reference by object name instead of by external file.

Recipe:

A material object names a material and records its physical, mechanical, optical, and thermal properties as attribute sets, plus a parent material and a data source — a reusable material library entry that regions can reference.

A constraint object stores a parametric expression (with an ID and a type) used by the parametric/constraint machinery to relate dimensions and enforce design intent.

A script object stores an embedded script (by type) that can be carried along with the geometry it relates to.