As I’ve already touched on basically any modern pipeline with a budget on polygons that isn’t intentionally going for a low-poly aesthetic is going to incorporate re-topology in some way. Re-topology itself being the process of creating a generally lower topology version (though there are some cases where you just want slightly different topology) of a more detailed high-poly mesh, which can then have the detail projected with a normal, ambient occlusion, cavity maps, thickness maps etc. In the end what you’re aiming for is to create the closest shape you can to the dominant topology of the initial object, with the lowest polygon count that still allows for proper shading and in the case of things that need to deform like character models, proper arrangement of edge loops.
So what then makes good topology? Well the same rules apply that normally would if you were working to a low poly pipeline. Keep all you can to quads, maintain edge flows in a fashion that follows the natural flow of whatever your topology is. For an organic model this generally means tracing muscle definition, making sure your edge loops terminate in areas where it’s easiest to hide, such as under the arms, or drawing in along the spine. If there are distinctive shapes along your high-poly, follow the edges in much the same way. The cleaner your edge flow, the easier you can attain good results when animating.
Most 3D suits these days come packaged with some tool that allows re-topology. Generally, unless the object is static, this will involve a fairly lengthy manual process of picking out topology quad by quad (or triangle) across the face of the original model until you have achieved the results you want. Given my workflow is so heavily reliant on ZBrush, I’ll go over a couple of the options available for making a sculpted object usable in a real-time engine in short order.
Firstly, in ZBrush alone there are a couple of options you can begin with. The ZRemesher tool provides powerful options for automatic re-topology and the ability more manually re-position verts or readjust rings as you can with the more general geometry overlay method of 3ds Max for instance.
The video below details how the ZRemesher can be used to quickly automatically re-topologise an object, or be set up to remesh following strict guidelines of topology density and specific edge loops.
I gave this a bit of a go myself, when trying to make some quick object for a turnaround deck. Though I just utilised the initial re-mesh because it suited the purpose well enough to get some rocks happening. Ultimately didn’t end up using it in favour of a more standard 3D-Coat arrangement (which I’m about to go over) but I’ll post it here anyway to illustrate the point.
This for many applications of stationary objects would be enough. If you were to take your time with the method shown in the video above it would also be generally suitable for animation deformation as well. I’ve become fairly accustomed to 3D-Coat as part of my pipeline, though, so I’ll go over a couple of the options that presents.
For Metum I went though a fairly slow but reliable approach with re-topology that saw me using the quad overlay tool to reconstruct the mesh. 3D-Coat does however also offer options similar to those we’ve just looked at in ZBrush, as far as being able to generate topology by drawing in guidelines and defining shapes for certain areas are concerned. It also posses a useful tool to drag out geometric standards over the top of your high-poly mesh that will then collapse inward to snap-to over the top, which can then be adjusted in small ways as needed from the existing geometry.
This method could very easily be used to re-topologise a more complex mesh in pieces as well. Extremities like arms and fingers on a character model could quite quickly be re-topologised and joined at the seams, for example.
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XY01,. (2016). zBrush: High poly sculpt to Low poly mesh and normal map workflow. Retrieved from https://vimeo.com/111813917