3D Toolkit: Retopology

Retopology
Retopology is the act of recreating existing surfaces with optimized geometry, in terms of memory usage. Also allows for topology to be fit for animation, allowing models to deform and move in a correct manner. To retopologise, we first decimate our sculpt, significantly reducing the polygon count, then export it as an FBX into Maya. In Maya, the Quad Draw Tool is utilised to create new faces over the mesh whilst retaining the shape of the model. 

When using the Quad Draw tool, TAB is used to extrude faces, SHIFT+LMB is used to smooth regions, CTRL+LMB creates an edge loop and you can weld vertices together by dragging them using LMB. CTRL+SHIFT+LMB deletes regions of the retopology.

In areas of sharp deformation, such as the eyes, shoulders and hips, it can be useful to consider creating topology in a series of concentric circles, allowing for more detailed deformation.

To demonstrate the retopology process, I have created a high-topology sculpt of an alien head. 


To decimate the model, go to Zplugin - Decimation Master. Decimation Master has several options that allow you to keep UVs. We then use the Pre-Process functionality. This allows ZBrush to identify which areas of a Mesh may be removed without adversely affecting the geometry.
We then use the decimation slider to determine how strong we want the decimation process to be, and finalise the operation.
We can then export the subtool as an FBX file.

In Maya, use File - Import to add the FBX file to the scene. When imported, FBX files may be small, so scale it appropriately.

Select head - when selecting snapping icons, indicated by magnets, select the last one without an icon. This turns the object into a "Live Surface". Then go into the Quad Draw tool, turn on symmetry, and draw in a quad. When points are drawn in, press SHIFT+LMB to create a quad or delete to remove the points. 


In Zbrush, the Zremesher can be used to get the effect of a quick retopology. This would not necessarily be as accurate as a quad drawn retopology, and as such may not be appropriate for a game ready character. You can use the 'Zremesher Guides' tool to add guidelines to a model showing how the remesh should flow over the geometry. The target polygon count can then be used to determine how much the mesh should be reduced.

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