Autopo (Auto Retopology)
Autopo lets you begin the process of creating new topology with a minimum of tools. You can determine much of the final result by properly using the settings found in the opening dialog box.
A temporary subdivision level that 3D-Coat uses for establishing an approximate level of detail that is needed to snap the final topological mesh accurately. You will find that the default setting works well for most situations, depending on your underlying object. But trial and error will help you to learn which value is best for any given object. Especially if the object is complex.
This value determines the final number of polygons that will be present in your automatically retopologized mesh. For example, 2500 is a typical value used in making game assets.
The default value is usually fine for organic models, and a value of 1 is usually better for hard surface model shapes.
In models where you desire more polygonal density (for displacement purposes), you can designate these areas with a selection masks. You paint these regions with the Freeze tool, or you can make more precise designations by using any of the Stroke Modes. In practice, it is often helpful to allow Autopo to determine its topology without assistance, just to see which areas need more guidance, (this applies for Topology Guides, as well). Sometimes no guidance produces the best results.
After a first pass with Autopo, you will be able to see more clearly which areas need your manual help. It’s easy to get carried away, masking too many areas to be scrutinized by the algorithm.
When no guides are placed by the user, Autopo usually produces good polygon flow throughout the resulting mesh, with no unwanted twisting. However, adding guides which do not reach far enough can result in this unpleasant twisting of edge loops and polygon rings.
The best practice, when dealing with organic shapes that have appendages (arms, legs, fingers), is to start and stop the guide lines before and after connecting joints, where a thinner piece of geometry meets a thicker piece (i.e. where an arm meets a shoulder or an arm joins a hand). In these cases, the guide should be drawn as a continuous line starting before the shoulder and extending beyond the wrist and well into the hand area. Fingers should be given guides that start and the tip and continue beyond the wrist, when possible (the longer the better). This helps eliminate any twisting.
In areas of your model where loop consistency is desired and there are no branching areas, use Through guides, longitudinally and laterally, starting and stopping the guide line outside of the mesh area. These guides will, by default, be straight lines and will serve to slice the model all the way through, saving you the time of drawing separate guides for the front and back surfaces. This type of guide works well in areas like the torso and within the girth of an arm or leg, for example.
When a Through guide is used laterally across an area like an arm, they will form complete loops around the arm.
Automatic UV Unwrapping
If you choose one of the automated options for Autopo that also Bake a depth map for the Paint Room, (“Autopo w/ Per Pixel, for example), be aware that UV seams and unwrapping of the mesh will be automated as well. This can often work out well, producing a UV Map with consistently sized polygons throughout islands. When you anticipate potential problems, it may be best to choose the simple the standard Autopo function and mark seams and unwrap your mesh manually, in the Retopo Room before Baking your mesh into the Paint Room.