3D Models of Assets

Assets composing a model of a factory also need to be modeled in terms of their 3D representation. To go in this direction, 3D models must be available. They can be obtained according to two main options:

  1. Use existing 3D models. 3D models of industrial objects are often available in online databases (e.g., GrabCAD) or directly provided by OEMs in official catalogs. These models are usually very detailed, thus an aspect to be considered is being able to end up with manageable models in terms of dimension and complexity. Furthermore, 3D models must be available in a neutral format (e.g. .STEP or .IGES), so that they can be easily imported in general software environments for further processing. IMPORTANT: 3D models downloaded from external sources are often constrained by privacy policies and rights preventing some or all their possible uses. This can prevent the possibility to publish this material on this website, even if not commercial use is foreseen. Please, before proceeding, check information about licenses and favor open licensing schemes.

  2. Generate 3D models. A second option is to generate 3D geometries using CAD modeling tools (e.g. Solidworks, Inventor). Although more difficult and time-consuming, consider this option to avoid possible issues related to licensing and rights.

Scaling and orientation

3D models in the scene have to be properly scaled. The hypothesis, unless differently specified, is that all the measures are expressed in millimeters (mm).

Furthermore, the orientation of each single component must be coherent with the other objects in the scene. In many CAD environments, it is possible to specify the convention used for the orientation of the z-axis (z-up option).

Grouping and referencing

Assets in a factory are often complex objects consisting of many components assembled together (e.g., a workstation). It is important to build 3D models in order to be easily and clearly composed to form complex assets.

It's important to have a univocal reference point for each asset in the scene. Namely, this point is the origin of the corresponding 3D model. Origins may often have unusual positions, especially when 3D models have been downloaded from online databases. To make the use and re-use of 3D models in the scene coherent, a reasonable solution is setting the origin in the central point of the bottom face of the bounding box of the component.

The positions of the origins can be used to define a complex asset by specifying the relative position of its components according to the following steps:

  1. Each complex asset will have a parent empty object to which its static components will be referenced and positioned.

  2. Subcomponents have to be grouped matching the hierarchy of the assembly, i.e., assets forming a sub-assembly must be grouped together.

  3. Parenthood relationships between the 3D models have to be defined specifying the associate relative positioning. CAD environments use this approach to manage multipart assemblies and dependencies.

Setting up the origin

This operation can be accomplished in CAD software such as Solidworks, or downstream when editing the exported GLTF/OBJ in Blender.

  1. Generate the bounding box of the 3D model.

  2. Make the central point of its bottom face explicit.

  3. Move the origin to make it coincident with the point.

Formalize information of assets using 3D models

The described procedure and conventions are used to derive information on 3D models to support the instantiation of assets by specifying their representation. It must be stressed that not all components in an aggregated object must be necessarily mapped to assets instantiated in the digital model (spreadsheet, JSON or ontology). Indeed, this mapping should be limited to components that are associated with needs in the following (non-exhaustive) list:

  • the placement (either position or rotation) is customized with respect to the default values defined in the 3D model file (e.g. GLTF file)

  • a description or any other property (type, model, connection, assignment) must be defined, as documented for spreadsheets and JSON files.

  • the component must animated independently of its parent. Static components typically are not associated with this need.

Please note that if a component is explicitly defined as an instantiated asset, then also its parent must be explicitly defined for the sake of consistency. In addition, a unique reference to the component inside the 3D model must be provided (e.g. adding '#componentID' to the file name, cf. "file" property in spreadsheet and JSON file). This means that also the ID of components in the 3D model must be uniquely identifiable.

Examples are provided in the use case section for an assembled product and a workstation.

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