Voxels versus Triangles

We’ve been studying the size of voxel versus triangle models recently. For really complex models we knew that the file size for voxels would be smaller. As you approach one triangle per voxel you end up using significantly more space to express the details. The basic information for a triangle is at least 3 floats to describe its vertices. Compared to using a bit or byte per voxel that quickly adds up. At Shapeways we are starting to see a bunch more data exhibits this type of density. Scanned data, digital fabrics and fractal art all push the limits of what triangle formats can comfortably express. We’re seeing files that compress down to 66% of the original all the way to 4%. This spreadsheet shows a small trial we ran to get an idea of the data.

File Size Results

Now you might be thinking that binary STL files are not the best way to pack 3D data. It’s true that you can find much better formats to transmit triangle data. But what you won’t find is a format that is more widely adopted. About 70% of all uploads are STL. Import and Exporter writers have voted and STL is it. I believe this is related to how simple and stable the format is. It’s a few pages of wiki definition and it hasn’t changed in years. Any solution that is going to replace STL will need to best it in key features and remain as simple to implement. It’s possible to write an STL reader or writer in a night and lots of people have done it.

So how does SVX compare when handling normal files? I’d like to define 3 classes of data. Simple data are models with 25K and make up the bulk of today’s 3D printed models. The last class are Complex data. These models approach the complexity available from a 3D printer. Shapeways sits on an interesting pile of user data with over 3 million user models in our database. For this analysis we took a small sample of user uploads, removed any duplicates and then analyzed models over 25K triangles. What we found was that encoding these models in SVX had an average of a 48% size from binary STL. While we don’t consider the main advantage of using voxels as a space savings operation it is heartening to know it won’t mushroom our bandwidth and disk bills. We’ll want to perform a deeper analysis of many more models to really characterize this change but we feel this gives us a good place to start.

As the industry moves to denser models and multiple materials we think a native voxel format for uploads is necessary. Our users are already pushing the envelope for triangle uploads and by switching to voxels we can enable much higher fidelity designs that will have complete control of each voxel the printer prints.

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