import 3d model in SceneKit on iOS

Question

I have a problem when importing a .obj file from a URL and convert it to a SCNNode

here's the code (swift3):

    let url = URL.init(string: "https://cloud.box.com/shared/static/ock9d81kakj91dz1x4ea.obj")
    let asset = MDLAsset(url: url! as URL)
    let object = asset.object(at: 0)
    let node = SCNNode(mdlObject: object)

but when i run the project, the console shows that:

Could not open OBJ file

how to deal with this?

score 4 · Accepted Answer · answered Oct 14 '16 at 22:51

4

I think you are exceeding some internal iOS limit with your OBJ file. Please file a report at https://bugreport.apple.com.

This slightly modified version of your code works perfectly in a macOS playground (Xcode 8.0). But in an iOS playground, I see the same "Could not open OBJ file" in the console.

import SceneKit
import ModelIO
import SceneKit.ModelIO

if let url = URL.init(string: "https://cloud.box.com/shared/static/ock9d81kakj91dz1x4ea.obj") {
    let asset = MDLAsset(url: url)
    print(asset)
    let object = asset.object(at: 0)
    print(object)
    let node = SCNNode.init(mdlObject: object)
    print(node)
}

I was able to download and open the OBJ file with Xcode. Then within the scene editor, I converted it to SCN format. That gave me a .SCN file that could be embedded in the iOS project and opened with SCNScene (like the famous spinning spaceship). So if you can live with embedding a static file in your iOS app, that's a way to get your model in. But if you need dynamically loaded models, it won't work.

answered Oct 14 '16 at 22:51

Hal Mueller

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Thank you, your answer really inspired me. I made a OBJ file by myself, and succeeded – ZHAO Yida Oct 15 '16 at 07:20
but if i want to avoid this bug, should i use OpenGL or something else to import OBJ file? – ZHAO Yida Oct 15 '16 at 07:24
OpenGL knows nothing about OBJ files. Neither does Metal. You are IMO tickling a bug or limit in ModelIO on iOS. Switching to Metal or OpenGL won't help. Do you have to load the model over the net? If not, simplest fix is to do the OBJ to SCN conversion on your Mac and embed the SCN file instead of using OBJ. – Hal Mueller Oct 15 '16 at 07:47
Unluckily i have to import the model from the net :( So now I had to go to report the bug. – ZHAO Yida Oct 15 '16 at 09:02
Were you ever able to figure this out? – humbleCoder Feb 19 '18 at 03:21
@humbleCoder were you? 3 years later and still the same error when loading .obj – Jubei May 26 '19 at 22:47

score 2 · Answer 2 · answered May 13 '18 at 09:25

By they way, if you had the obj file locally, you could just have used:

guard let url = Bundle.main.url(forResource: "ock9d81kakj91dz1x4ea", withExtension: "obj") else { return nil }
    let asset = MDLAsset(url: url)
    let object = asset.object(at: 0)
    let node = SCNNode(mdlObject: object)

score 1 · Answer 3 · answered Jun 13 '19 at 00:17

This should let you load an obj/dae file in swift 4.2/xcode 10.2+:

Create a scenekit model catalog by going to File --> New --> File and selecting "SceneKit Catalog" from the list.

import SceneKit.ModelIO

Then:

guard let url = Bundle.main.url(
 forResource: "your_obj_filename",
 withExtension: "obj",
 subdirectory: "your_folder.scnassets") 
     else { fatalError("Failed to find model file.") }

let asset = MDLAsset(url:url)
guard let object = asset.object(at: 0) as? MDLMesh 
     else { fatalError("Failed to get mesh from asset.") }

let newNode  = SCNNode(mdlObject: object)

import 3d model in SceneKit on iOS

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