Retopology

Retopology... retopologization... however you slice it, it's a difficult word to say. But immensely useful to actually do. For example, most items that have been scanned by a device have an ugly, ugly mesh. Usually very dense, and all triangles.

This is a mesh from a femur that was edited in Mimics. It is from a CT data set, taken from the skeleton that I'm currently modeling. Mimics is a program similar to OsiriX - it can take DICOM data (CT, MRI, etc) and export a file that can be read by a 3D program. This is wonderful for achieving highly accurate models, but not so good for clean meshes.















The .obj file is being viewed in a program called MeshLab. It has the ability to handle high-polygon meshes very well.















The femur that I am working with exported with around 139,000 faces. This actually isn't that bad, comparatively speaking. I've easily come across a 4 million poly export from a DICOM program. Even so, this mesh would be a pain to texture and animate with.

This is Zbrush. My main love for Zbrush (and it's a recent discovery) is the retopology tool.















By drawing new polygons on the surface of your high res model, you can export a low res stand-in. The model that I generated has 3,200 polygons. A far cry from 139,000.















I could have made it with fewer polygons, but I found that the mesh reacted best to a slightly denser layout. Perhaps because I'm new to this whole retopology endeavor and haven't learned all the tricks yet. I do have an entire skeleton to work on, so hopefully I'll continue to learn.

The wire frame is now as clean as you make it, allowing for potentially great edgeflow. This makes texturing and animating much, much simpler.


















However, this is not what I find the most useful attribute of retopologization. Zbrush allows you to project your original high res mesh back onto the low res model. By matching how many times you up the density during retopologization, subdiving the low res obj that many times again, and then importing the high res mesh on top of this highest division, it becomes a smooth stepping process between the lowest and highest resolutions.















Did that sound complicated? It was very fun for me to figure out, let me tell you. If it didn't... well, you are smarter than I am. Kudos.
















In any case, there are tutorials out there on the retopology tool. If you are interested in my entire workflow from Mimics/OsiriX to Zbrush, let me know.

















These images that you see are screen shots of the femur as exported from Mimics. I have not done any further editing to it yet. I plan to do so, of course. I will post more images as my bones are completed.