IMPORTANT! This feature is a BETA feature and as such you may encounter bugs/issues, which should be reported.

The model attachment feature permits you to reference a model glTF and its corresponding XML file as an attachment to a main model. For example, with an aircraft model you may want to have various passengers and traditionally you would have to add these into the actual aircraft model for them to be shown. However, with the model attachment feature you can create a passenger glTF, then write a model.xml file for it, then attach this to the aircraft at a specific node.

NOTE: This functionality is currently not supported when using The Blender Plugin.


The benefit of this system is that the attached model is not merged into the aircraft itself, and so has its own set of LODs and animations that can be set differently to those of the aircraft itself, which can greatly improve performance. Using the aircraft passenger example again: your attached passengers may not be close to the camera and so it can be on LOD2, while the aircraft itself is on LOD0, meaning that fewer polygons are being rendered.


Note that this is not the same as the Submodel Merging feature, since the glTF files used for attached models can have a distinct hierarchy and will have the LOD limits applied to them independently, while sub-models need to maintain the hierarchy and LOD levels of the original "main" model.


When working with model attachments, it is worth noting the following:


  • attachments need to be attached to every LOD individually. However, unlike submodel merging they are not duplicated for every LOD. Instead, the attachment is reparented (moved) to the currently active LOD.


  • attached models are described with a model info XML file and as such can define their own LODs.


  • Modification of "minSize" based on LOD Minsize Rules is always applied to attachments, and applies in the same way it applies to regular models.


  • attachments use the Sim of the SimObject they are attached to.


  • Attachments use the texture directories of the SimObject they are attached to.


  • the last LOD of a model may not have any attachments.


  • LODs that have a "minSize" of less than 5% may not have any attachments (this is to encourage merging meshes at that stage, for performance reasons).


  • attachment IDs must not start with an underscore _, this usage is reserved.


  • all models that are to be attached to the main model, must be part of the same project in the Project Editor. You cannot attach models from other projects.



You can find a basic example setup of a model using attachments on the following page: