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STL binary export has "solid" at beginning of file

Question asked by Bryn Wolfe on May 16, 2019
Latest reply on May 22, 2019 by Artem Taturevych

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I export my Solidworks files to STL for use in other rendering apps. I always do this in binary to reduce file size. In some situation I want to look at the ascii equivalent so tried to convert the Solidworks-generated binaries to ascii, but every application I've tried fails to understand the file. Based on what I've read on the STL wiki at STL (file format) - Wikipedia , it suggest that a binary stl should NEVER start with the word "solid" because that's how most of them determine if the stl file they're loading is ascii or binary. Well, Solidworks puts "solid" at the beginning of every stl, binary or ascii, so I consider this a bug. Any chance this can be fixed?

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Paul Salvador May 16, 2019 11:37 AM
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Hello Bryn,.. not sure but what programs are you having problems with?
I tested just now,.. and I can open in Blender, IdeaMaker, FreeCad, SketchUp, Rhino3D, MeshLab,..
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- Frederick Law @ Paul Salvador on May 16, 2019 11:26 AM
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  Plus Cura.
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- Bryn Wolfe @ Paul Salvador on May 16, 2019 11:46 AM
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  It's the conversion apps I tried, such as convertSTL GitHub - cmpolis/convertSTL: A utility for converting STL files between ASCII and binary encoding. from github and from STL files: Convert from ascii to binary and the online converter at Online Mesh Converter . Perhaps their implementations are simpleminded, but 3 out of 3 fails forced me to investigate the nature of the binary stl files exported from Solidworks and when my hex editor showed the word "solid" at the beginning of the file, I figured that's probably the culprit.
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  - Paul Salvador @ Bryn Wolfe on May 16, 2019 11:54 AM
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    Hey Bryn,.. when I view the stl, in the first line, it does include the word Solid along with the name of the file.
    It could be, the converter you are using does apply a stringent rule and the above programs skip the first line?
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    - Bryn Wolfe @ Paul Salvador on May 20, 2019 9:37 AM
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      Those apps I tried are probably overly simplistic, but does solidworks really need to put the word "solid" at the beginning of a binary file? If they could just put anything else there, e.g., "bsolid", these conversion apps would work. Need to find a proper binary file editor to test this.
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      - Chris Dordoni @ Bryn Wolfe on May 20, 2019 11:19 AM
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        Bryn,
        
        If the exported object is a surface (ie non manifold), it will read "surface" instead of "solid".
        However, I believe this is ignored by the reading application for the binary format.
        
        The ASCII version of STL is rarely supported so it not surprising there are issues in many applications.
        In that version, multiple objects in one file were required to be uniquely identified for the reading application.
        
        Can you describe what you need the ASCII version for?
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Frederick Law May 16, 2019 11:53 AM
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Inventor does create STL binary without "solid" in header
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Artem Taturevych May 22, 2019 5:59 AM
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I have a macro which exports selected component to stl without built in translator, i.e. STL composed as per spec: Export selected component to STL using SOLIDWORKS API

I can modify it to work with active model as well if that would help.
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- Bryn Wolfe @ Artem Taturevych on May 21, 2019 8:35 AM
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  Interesting, I'll keep this in mind. My original motivation for looking into the nature of the solidworks stl output was to ascertain the nature of the surface normals. I'm actually importing these models into an Unreal Engine application and find that the normals are defined one-per-triangle (as the STL file format dictates), but this is not great for rendering as it doesn't allow for any shading consideration. What's really needed is something that considers the nature of the solid model itself when generating the mesh and normals, but the STL file format doesn't support that. Perhaps another format is better at this, like collada.
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  - Chris Dordoni @ Bryn Wolfe on May 21, 2019 9:35 AM
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    I haven't worked much with SW2019 so perhaps there has been an improvement...however, the mesher in previous versions has very little control over the quality of the resulting mesh, particularly for rendering applications.
    
    If this is your goal you might have a look at Moi3d or Rhino to produce better meshes using a nurbs export from SolidWorks.
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  - Frederick Law @ Bryn Wolfe on May 21, 2019 9:41 AM
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    I suggest using other format.
    STL was designed for 3D printing. So its doesn't have any other function or information in the file.
    STL should be used as designed: 3D print.
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Artem Taturevych May 22, 2019 5:59 AM
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I have updated the macro. It can now export active part and also (optionally) reorient the output.
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STL binary export has "solid" at beginning of file

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