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I have an odd situation with an object converted from a .wrl file of a Minecraft building. After remeshing to make the object manifold, it seems to have created a "hollow" object - that is, there is an outer facing layer on both the outside and inside of the object. This is kind of confusing so here are some images:

Here is the bottom corner of the building from the outside. "Outside" facing parts of the faces are highlighted in blue by Blender for clarity. Exterior

And here is the bottom corner of the building from the interior. Notice it's still blue, which means there's another layer of "outside" faces pointing inside the building. enter image description here

Finally, here is a GIF of me going from the exterior to the interior of the building from the bottom a couple times. Notice the red coloring signifying the inside pointing parts of the faces. enter image description here

My guess is since Minecraft is made of blocks, it's considering the inside of a block to be the "interior" and every face of the block touching air the "exterior", including the faces that are facing the inside of the building. I think this is why when passing through the floor, it showed red.

My goal is to 3D print this building, so I am only concerned about the surface of the building itself. I don't care about its hollow interior. In fact the hollow interior should be infilled by the slicer program, which it is currently not due to this issue.

How can I either make the imported building manifold to begin with so I don't have to remesh at all? (I've tried a handful of things to no avail here like merging vertices by distance, the 3D print toolbox addon, etc.) Or if that's not possible, how do I get rid of everything except the surface of the building - any faces touching 'air' so to speak. The mesh should just consist of what is visible from the outside. Any solution to get this object 3D printed is fine with me.

Thanks!

Edit: I'm linking to an example of a smaller imported Minecraft build with identical problems (one seen in pictures above is too large a file): .

NDrummerboy087
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  • There are a great deal of inner faces within the "hollow shell" - look inside this top of the dome tower - there is a second floor. Inner faces like this will confuse blender. – Christopher Bennett Dec 24 '22 at 02:13
  • In edit mode, try hovering your mouse over a face on the inside and hitting L If it selects all the inside faces only you can simply delete them – Psyonic Dec 24 '22 at 02:18
  • Right, there are interior faces all throughout which seem to equate to the inside of Minecraft blocks. How can I get it to ignore the inside of the building and just consider the outer surface? – NDrummerboy087 Dec 24 '22 at 02:19
  • Psyonic, thanks for the response. It seems to select a disorganized mix of both in my case – NDrummerboy087 Dec 24 '22 at 02:28
  • I see your model now, yeah, that's a mess. Why don't you want to re-mesh? That is what that tool is for after all. – Psyonic Dec 24 '22 at 02:54
  • For some reason if I remesh with enough detail to actually print, it does the thing where it has the two “outside” facing faces on the exterior and interior of the model. This makes it hollow and thus the slicer doesn’t infill the empty interior space. The images shown in the question are from the remeshed result. – NDrummerboy087 Dec 24 '22 at 03:20
  • Ok... I did a re-mesh of 0.1, then added a decimate modifier with ratio set to 0.05. This took some time to compute but SuperSlicer looks like it sliced it just fine :) – Psyonic Dec 24 '22 at 03:36
  • Hmm I will try that on the model from the question. Is it possible to send the file for that model? It’s 70 MiB but the Blend Exchange max is 30 which is why I used that smaller example file. Which other options did you have set from the decimate modifier as well? – NDrummerboy087 Dec 24 '22 at 04:05
  • I find it frustrating that Blender has no way to select faces that are essentially exposed to the outside world. This feature is missing. L will not do the trick. There must be some algo available that selects all faces that can be hit by light and your model is the perfect example for the test. Even the select box tool will not work, it is supposed to select only what is on the outside like this but it ends up selecting faces on the inside as well which is incorrect behavior. – Harry McKenzie Dec 24 '22 at 07:46
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    Harry, I totally agree. I’ve tried so hard to find a way to do this and at first I thought it would be easy since it seems like such a basic and common case. But I guess I was wrong. – NDrummerboy087 Dec 24 '22 at 16:28

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