Retopology

Retopology is the approach of basically tracing the high polygon asset manually and creating a low polygon model. You have complete control where every polygon goes and you can make it 'neatly' with good edge loops so you can add/reduce polygons as needed much more easily. This also makes it much easier to unwrap for texturing.

This approach is basically required for characters as posing and animation usually plays a part, and the edge loops play an important role in how easy it is to rig, or apply to a skeleton, as well as how good it looks when posed or animated. So keep this technique in mind if you are looking to create VRM Avatars.

The simplest way to do this is by creating a separate model, a simple box or a single polygon plane for example, and then use the snap tools to place and extend polygons over the high polygon manually. This does take longer but the results are also much better and cleaner than using decimation or remesh tools.

As this is a more complicated approach, I will add two videos below. One is reducing a curved asset made in Rhino in Blender, and the other is one of the Workshops that cover optimizing Photogrammetry. This also covers 'baking' the high polygon asset onto the low polygon asset so that the textures can help pushing the detail to basically represent the original model exactly with a significant reduction in polycount.

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