Retopologizing An Organic Model with ZRemesher
In this blog post, I'm going to show the basics of retopologizing a model using the ZRemesher tool in ZBrush. Including some tricks that can be employed to tweak the topology if the initial redo isn’t quite right. This tool is capable of being used on both hard surface and organic models, but I will focus solely on what can be done to create proper retopology for organic models. ZRemesher can be used on nearly any existing model, regardless of subdivisions or how the topology is broken up. Even the mess that is Dynamesh can be corrected using this tool.
Dynamesh Head
Creating the initial retopology for a model isn’t too difficult. In this example, I am using the DemoHead that can be found in the Project section of the Lightbox. I changed the model to Dynamesh, to show how the ZRemesher can clean its messy topology. To use the tool, go to the Geometry palette, click the ZRemesher section, change the settings to whatever you desire (a few of these will be explored further later in this post, to perform a few useful tricks) and then click the ZRemesher button. If there are still too many polygons, clicking the Half button and remeshing the model once more will lower the polygon count. On the other hand, if there are too few polygons and it is causing details on the model to be lost, clicking the Double button would fix this.
Retopologized Head
Of course, if a higher polygon count is not wanted, the Adaptive Size could be changed to try and help the model keeps its detail. The higher the Adaptive Size is, the more flexible the topology of the model will be. Although, this comes at the cost of a higher chance of triangles being added to the mesh instead of quad polygons. Normally the default setting of 50 is perfectly fine to use, but there may be times when the model requires a higher setting to retain its shape and details. Low Adaptive settings create square polygons that are all around the same size. While a Higher Adaptive setting allows the polygons to stretch into rectangles to better fit the model’s shape, and their size will not be as consistent. Smaller ones may be created in areas where a denser mesh is deemed necessary. For example, here is the model with a much higher Adaptive mesh.
Topology with 100 Adaptive Size
Another helpful tool that affects the rigidity of the model’s topology is the Curve Strength. The lower Curve Strength is, the more flexible the ZRemesher will be when creating the new topology. The higher the strength is, the curves stop being considered merely guidelines and become concrete rules. The ZRemesher Guide brush can be used to create edge loops on a model (such as around a character’s mouth) to help ensure that the topology is correct around these areas. It can also be used to fix spirals that can sometimes be found in the mesh.
These spirals tend to appear in places such as arms, legs, and fingers because of their tubular shape. Thankfully, this can be easily remedied with the use of the ZRemesher Guide brush as well. Simply go to the Tool pallet, go to the Geometry section, click on ZRemesher, and change the Curve strength to 100. This forces ZRemesher to replace the spiral with an edge loop. However, there is a chance that creating this edge loop will cause a spiral to be created on another part of the model. Not every model is guaranteed to be able to be retopologized completely free of spirals.
Example of edge loop created by the ZRemesher Guide brush
If there are certain parts of the model’s topology that needs to be fixed, Partial Mesh retopology allows these changes to be made without affecting the rest of the mesh. First, the Lasso selection tool needs to be selected, so that the area that needs to be retopologized can be isolated from the rest of the model. Make sure that the settings in the ZRemesher options are correct. If Freeze Border is being used, then the Target Polygon count does not matter as much because ZRemesher is going to have to match the border of the hidden mesh regardless. This is to be sure that the new topology merges properly with the original. Once the ZRemesher button is clicked, the model will be visible again with the new topology connected to it. For example, the Dog that can be found in the Project section of the Lightbox has double the number of polygons in its head than its body.
Example of Partial Mesh retopology
In conclusion, ZRemesher is a wonderful tool to use when cleaning up the topology of a model. With helpful features that can be tweaked accordingly to get the best mesh possible for both hard surface and organic models. These are only a few of the things that can be accomplished using the ZRemesher, and it is definitely a tool worth exploring further.
