A special treatment for 3d models in glb/gltf format is implemented in the Binaries Service. 

If URLs to files of this format are submitted to the service then these files will not only be downloaded and saved. A preview image of the model contained in the file is generated and exported to the IIIF Image server. Therefore the same reference-id used to download the model can be used to retrieve a preview image. 

This preview generation happens on the cluster nodes. A Chrome browser instance is started on a virtual framebuffer device. The model is loaded by the browser and then a screenshot of the browser is taken. 

In order for this to work the follwing packages need to be installed on the cluster nodes: