@tig said:

Unless you want to 3d-print this the reversed faces are somewhat irrelevant.

@nikopol said:

"I need them to be perfectly oriented in order to 3D-print the object."

That's the crux of the issue. While the STL file I receive is generally printable, any reversed faces do not print and instead generate unsightly artifacts. Unfortunately, none of the other programs I use to clean STL files, such as MeshLab, Netfabb, Meshmixer, Chitubox, or LycheeSlicer, are able to fix the reversed faces either.

Regards, Roger

This is a model I have already spent a lot of time on, manually reversing some of the faces. However, I still have 200 more to clean, so I need to find an automated solution to get this done.

http://www.kaestle.ch/files/H10_test.skp.zip

Thank you, and regards,
Roger

@dave r said:

What is the source of the geometry for your model? Perhaps the best thing would be to go back to the source and correct the issue there.

That's the issue: the buildings were sourced from public data files. I don't encounter any problems with incorrectly oriented faces when working with my own files.

However, what I find confusing is that even though SketchUp is able to identify these faces as blue faces, they are not selectable. I'm curious to know the reason behind this limitation.

Given that I've tried various plugins already, I can imagine that the developers must have also experienced similar frustrations when trying to program tools to select wrongly oriented faces. It seems illogical to me that none of the plugins are able to select them with 100% accuracy.

Currently, I'm dealing with models containing more than 250,000 faces, of which 10% are reversed. I have yet to find a satisfactory way to combine the available tools to achieve the desired result.

I've been using SketchUp for around 15 years as an architect, incorporating it into my daily work routine. Over the course of my career, I've rendered and 3D-printed hundreds of projects, but have always been frustrated by the issue of reversed faces, which can be soul-crushing to deal with. While I've tried numerous tools to fix this issue, I'm currently facing a project with thousands of faces that are not properly oriented. Unfortunately, fixing them all manually is not an option for me, as I need them to be perfectly oriented in order to 3D-print the object.

What I find puzzling is that SketchUp is able to depict these incorrectly oriented faces correctly as blue faces in its monochrome face style. However, neither SketchUp nor any other tool I've tried can seem to select and reverse them all effectively, often causing some of the correct faces to be changed as well. It's a real mess. Nonetheless, I'm curious as to why SketchUp is able to display these faces correctly despite the difficulty in selecting and reversing them. Perhaps some developers out there could shed some light on this issue and recommend the best tool to correctly orient faces. (I'm currently using SketchUp 2020-2022 on an Apple M1 Max with 64 GB RAM and macOS Ventura 13.2 (22D49)).