Exporting the edges works but all meshes with smoothed edges turn full black as if the normals where inverted.
What do you mean with “if the normals where inverted”, if you invert normal then you change also ligting so only inside of mesh will get lights (if there is a light source). Probably this is why you get black/unlit mesh.
Recently I also used ARKit + SceneKit + COLLADA to show a model with ARKit, I converted COLLADA to .scn (with Xcode tool, in Editor menu) file in Xcode to edit some attribs.
Apple adopted/implemented COLLADA and it works perfectly with Preview.app, Xcode, SceneKit…
So basically you are saying that I cannot do anything to fix this right and I should forget Collada right?
Maybe SketchUp can’t export lines correctly, maybe you just can’t render it correctly… maybe you render it but you cant see it because of line width, color… anything is possible here
I’m not expert of SketchUp (I just downloaded trial version, probably I need a license now) but I’m glad they have COLLADA exporter. I’m working on an importer so SketchUp-exported files helped me a lot.
I think you need to render mesh as fill mode then lines mode/wireframe, or you could render lines primitives if SketchUp exported them. Maybe you need to set line width / polygon offfset to show lines (in OpenGL). Or Unity has ARKit plugin if you know/like it, it may save you from renderer stuff
In SceneKit I found this: https://developer.apple.com/documentation/scenekit/scnmaterial/2867442-fillmode
ARKit comes by iOS 11 so maybe this will help
Maybe you can try to export to another format then use it, but I think you may get same results if renderer side is not meet to your requirements (with lines).
I think it’s good advice to always avoid COLLADA
Apple (OS X / iOS) developers can still use COLLADA to import things (scene, mesh…) to Xcode, SceneKit (it is easy, fantastic in small, non-game projects), so technically it is not abandoned by Apple, I hope :D. Recently I downloaded some models from SketchUp 3D warehouse as COLLADA then used them. So it is very good to be able to open very old files as COLLADA, maybe it is complex and buggy but it is stable and ISO standard