I read several tutorials how to place 3d objects in SceneKit/ARKit applications and all of them uses .scn format files for the objects.
But I found there is no any issues if I use original .dae format and do not convert it to .scn format.
I don't really see any difference between .dae and .scn formats.
Actually result seems to me the same but can you explain what the difference between them and what I should use in what cases?
Thank you!
DAE (Digital Asset Exchange, aka Collada) is a vendor-neutral format for 3D assets. It supports a wide range of features that exist in multiple 3D authoring and presentation tools, but not every possible feature in SceneKit. Historically, it was the only asset format for early versions of SceneKit.
SCN format is a serialization of the SceneKit object graph. (There are convenience methods for reading/writing it on SCNScene, but really it's the same thing you get by passing an SCNScene to NSKeyedArchiver/NSKeyedUnarchiver.) Thus, it by definition supports all features of SceneKit, including physics, constraints, actions, physically based cameras, and shader modifiers.
If you're using DAE assets, deploying to iOS (or tvOS or watchOS), and not seeing any difference vs using SCN assets, there are two possible reasons:
When deploying to iOS/tvOS/watchOS, Xcode (via scntool) automatically converts all 3D asset resources to SCN format. (And applies other transformations, like interleaving geometry buffers, for optimal rendering performance on iOS/tvOS/watchOS devices.) The filename in the built app's Resources directory still has a .dae extension, but the file contents are the same as SCN format.
(SceneKit running in iOS/tvOS/watchOS actually can't read DAE, so it relies on this preprocessing by Xcode.)
The most effective 3D format that you can use in SceneKit/ARKit is a USDZ format.
USD – Universal Scene Description, was developed by Pixar. The file has the ability to create a 3D scene by composing many sources files together into successively larger aggregations. This is great but this could be a problem using USD to deliver assets in the form that they have been built up. There is a no mechanism for representing images/textures as scene descriptions encodable in USD files. Also these assets can be delivered on a variety of systems and platforms if it's a single object, can be streamed and usable without unpacking to a filesystem.
SceneKit framework supports several popular 3D file formats at the moment (geometry saved in these formats is visible in ARSCNView):
Collada's Digital Asset Exchange .dae
Pixar's Zipped Universal Scene Description .usdz
Pixar's ASCII Universal Scene Description .usda
Pixar's Binary Universal Scene Description .usd, .usdc
Wavefront Object .obj along with material .mtl
Alembic interchange file format .abc
Polygon File Format .ply
Stereolithography File Format .stl
SceneKit Scene .scn
Also you can convert .fbx and .glTF files using command line.
And about Reality Composer formats
.rcprojectand.realityread here.
