Glossary

The vocabulary of the whole project: the profile, the workflow, the reference pages and the tools. A term means the same thing wherever it appears.

Within the profile these definitions govern and supersede any other meaning the terms may carry elsewhere. Terms drawn from glTF keep their glTF meaning and are not redefined here.

Terms

assembly

A collection of parts and the joints between them. Out of scope: an assembly is expressed by the consuming project in its own description format, never in delivered geometry.

“Part” and “assembly” are this project’s own terms and no standard defines them. The closest published vocabulary is ISO 10303 (STEP), which distinguishes a part from an assembly the same way for mechanical product data; the usage here is consistent with it but does not depend on it.

asset

Avoided in normative text, except in asset coordinate system. In 3D work the word spans meshes, textures, rigs, scenes and library entries at every scale, and glTF itself uses asset for the metadata object inside a file, so it cannot be used precisely. Where the profile means the delivered file it says visual model; where it means the glTF object it writes asset in code font.

asset coordinate system

The coordinate system a delivered file is expressed in: glTF’s own, right-handed, +Y up, +Z forward, −X right. A consumer reaches the part coordinate system from it by the fixed rotation in the profile’s Axes section. Also called scene space.

base part

The part that establishes a vehicle’s reference coordinate system. There is exactly one per vehicle, and its manifest declares gltfrp:partRole as base. The profile requires a base part to name its datum point.

commission

The document the integrator writes in step 1 of the workflow, stating what is to be modeled: one vehicle or one batch of parts, with one block per part. It is the written statement of intent that a delivery is checked against. As a verb, to commission is to write and agree that document.

component part

A part that attaches to a vehicle’s reference coordinate system and does not establish it. Its manifest declares gltfrp:partRole as component. See the profile’s component part section.

consumer

A program that loads a delivered visual model. For this project the consumers are Gazebo and RViz.

coordinate system

Used throughout in preference to frame and to space. All three are in use elsewhere (REP 103 says frame, ISO 9787 says coordinate system, graphics says space) and they are treated here as naming the same thing. Where an external document is quoted its own word is kept. What each coordinate system here is called in ISO 9787, in REP 103 and in glTF is tabulated in the coordinate systems reference.

datasheet

The published source a part’s dimensions are cited from. The integrator chooses it in step 1 of the workflow and measures against it in step 3.

datum

A feature or set of features of the part that define the coordinate system reference - the location of the origin. The profile’s Datum specification section states which features may serve and requires that those named together fix all six degrees of freedom. A datum is named before modeling starts; it is not measured from the geometry afterwards.

datum coordinate system

What a datum specification evaluates to against a particular piece of geometry. In a conforming delivery its origin is the origin of the file, of node space and scene space, and of the part coordinate system. The profile’s Origin section says so normatively.

One origin, several coordinate systems. glTF distinguishes node space, the coordinate system a node’s vertices are expressed in, from scene space, what node space becomes once node transforms are composed down from the root. The profile’s Scenes and nodes section requires exactly one node carrying no transform, which collapses that distinction: node space and scene space are the same thing in a conforming delivery, the asset coordinate system. The part coordinate system shares their origin and differs by the fixed rotation in the Axes section, glTF’s axes onto the robotics axes.

datum point

The single geometric point feature of a part that fixes the location of its coordinate system, stated before authoring begins and recorded in the manifest. See the profile’s datum point section.

delivery

A single .glb file carrying a single part. See the profile’s Delivery section.

integrator

The party who commissions a visual model, checks it and integrates it as a robot component.

manifest

The metadata a delivery carries about itself, expressed as KHR_xmp_json_ld and attached to the glTF asset object. It is written from the commission by gltf-manifest. See the profile’s manifest section.

modeler

The party who authors and delivers a visual model.

origin

The location and orientation of the datum coordinate system relative to the visual geometry. Not a point chosen at the keyboard and not a measured property of the mesh: it is what the profile’s datum specification evaluates to.

part

A single physical component, geometry only, no joints. The unit the profile delivers. A part has a coordinate system and a place in an assembly.

part coordinate system

The robotics coordinate system of a part: +X forward, +Y left, +Z up, per ISO 9787 §5.5 and REP 103, with its origin at the datum point (Origin). It is the link coordinate system a consumer places the part in. The delivered file is not expressed in it; the file uses the asset coordinate system, and the consumer applies the fixed rotation in the profile’s Axes section.

submesh

Gazebo’s word and SDF’s, not a glTF term and not an assimp one. Gazebo’s loader turns every glTF primitive into one submesh, and SDF’s <mesh><submesh> element selects one by name. The project’s documents say primitive and use this word only when they mean Gazebo’s object or the SDF element. See the profile’s Primitives section.

visual model

The visual geometry delivered for a part: the file <part>_visual.glb and its contents.