Hello @inf800​ , thanks for posting! It looks like we only offer an Esri Indexed 3D Scene Layer (SLPK) Writer, but not reader at the moment, sorry to be the bearer of bad news! You should consider posting an idea to add Reader support for SLPK.

I also didn't see a format writer for the PLY format, but I did see an idea to: Add PLY - Polygon File Format to FME Workbench. Perhaps you could add a comment or upvote the idea to show your interest! Hope this helps, Kailin.

Tbh I've searched a lot and couldn't find a reader for SLPK to convert it into 3D model for softwares other that what ESRI owns - for example blender.

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So having this reader may definitely give your product an edge ​(given you've already cracked how SLPK format works with your writer)

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Having SLPK model and not able to open it in opensource tools like unity or blender or webGL is a huddle for multiple solutions.

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This is what ESRI team member has to say: ​https://community.esri.com/t5/arcgis-pro-questions/converting-scene-layer-packages-to-3d-models/td-p/409008