With the use of a couple of plugins, both Omeka S and Omeka Classic allow you to incorporate 3D models into your digital exhibits. Getting both your site and the 3D models in the proper form, however, takes a bit of work, particularly for Omeka S.
Install Necessary Plugins
While both Omeka S and Omeka Classic display 3D models using the Universal Viewer plugin, there are a few others that are necessary to ensure the framework is properly set up.
Plugins/Modules to Install in both Omeka S and Omeka Classic
Universal Viewer - This is the actual viewer that can display both 3D models and normal images/pdfs/etc. Its design is much nicer than the standard Omeka presentation view.
Archive Repertory - Keeps original names of imported files and puts them in a hierarchical structure (collection/item/files) in order to get readable URLs for files and to avoid overloading the file server.
Additional Modules for Omeka S
IIIF Server: Integrates the IIIF specifications to allow you to share instantly images, audio, and video.
Image Server: A simple and IIIF-compliant image server to process and share instantly images of any size in the desired formats.
As of the writing of these instructions, installing the Image Server module required the ability to directly access and install the module on the server, rather than copying the filer over using the FTP/SSH and installing from the Omeka Module page.
Preparing Models for Omeka
To display 3D models, we use the Universal Viewer plugin, which uses the ThreeJS library to display the models. This means that the model needs to be in a .json format to upload the file to Omeka. There are a variety of ways to do this, but an easy method is to use the ThreeJS editor.
Open the ThreeJS Editor Link.
Upload your 3D model (OBJ, gltf, etc.) by going to File --> Import and navigating to your 3D file.
The mesh (geometry) of your model will appear. The next step is to attach the texture (color overlay) to the model, if it is not already integrated into your file. To do this, click the "+" next to the name of your file on the top of the right sidebar and select the material associated with it (generally "material_0"). Then choose the "Material" tab below.
From here, where it says "Type," select "MESHBASICMATERIAL," which should be at the top of the list of choices. Next, click the dark rectangle next to "Map" a bit further down the sidebar, and navigate to your texture (usually a .jpg, if you are uploading an obj). Finally, check the small box next to "Map" and the texture should appear.
Your model should look good now! The last step in the editor is to go to File--> Export Scene, and the model should be exported as a .json to your downloads folder.
ThreeJS Editor Options
Uploading your Model to Omeka
Your model is now in the correct format (.json) to be uploaded to Omeka. In each case, you will want to be sure that JSON extension and the application/JSON file type are allowed (in Omeka Classic, go to Settings--> Security from the top of the Admin dashboard; in Omeka S, go to Settings in the Admin sidebar and scroll down to the Security section).
Now just create a new Item as you would any other item in Omeka, with the .json file as your main file upload! Note that if you want a proper thumbnail in Omeka Classic, you should upload two files for your item, first a normal jpg of the thumbnail you want to use, and then the .json file of your 3D model. In Omeka S, there is an option when creating your item for adding a thumbnail image if you wish.