Introduction to concepts in Retopology
Blog — Blender Assistance Community
Disclaimer: This blog is a project for Study Unit DGA3008, University of Malta.
Introduction
In this blog post, I will be going over the basics and essentials of retopology, why we should care about having good retopology, and what it entails. I am not an expert on this subject but am currently reading for a course in Digital Arts, in which I was exposed to and taught about this topic. As it goes for anything concerned with learning, it is recommended that you the reader actively participate and experiment on your own by putting the following content into practice. As always, although knowledge of how to use Blender is not necessary to get some understanding from this blog post, I will be making mention of particular terminology in order to contextualize this content more clearly.
Why have good retopology?
Most notably in animation, good retopology is an essential part of the process, which will dictate whether you will end up with a well-animated character or not. As such when modeling for animation it is recommended that you are aware of how to go about creating the new topology for the character as it will help streamline the process greatly and prevent the countless hours of frustration that would come from constantly having to fix issues.
Apart from retopology for animation, having correct topology will help in achieving high levels of detail with the minimum required number of polygons, resulting in an optimized mesh.
Also as the topology of a surface dictates how light will bounce off the surface, the clean topology will help in reducing artifacts and in calculating more natural shadows.
Surface Flow
When first thinking about Retopology it is important to take a step back and explore the concept of Surface Flow, as this will give us a better idea of what we should be aiming for when creating the topology of a mesh.
Surface Flow essentially entails being aware of how the movement of muscles and bones affects how the skin on top. Skin will respond by bending, stretching, flexing, pinching, etc. being more scrunched up in areas such as an armpit, where high levels of deformation will occur versus say a relatively flatter area like the upper back which will generally (and hopefully) remain somewhat fixed.
This does not mean one needs to learn all the anatomy that makes up a character (although probably useful), but rather be mindful of how topology (mesh surface) interacts with movement.
Edgeloops/Edgeflow
Good topology becomes apparent when looking at the Edgeflow. Edgeflow or Edgeloops are defined as a set of connecting edges on the surface of a mesh, with the word loop implying that the first and last edge meet to close the loop. Identifying these loops in your mesh first will make things a lot easier in the long run.
The image below shows the common Edgeloops used in retopologizing the hand, which will help in getting good Edgeflow.
Faces and Edges
Now that the basis for achieving good topology is set it is important that we look into how to best distribute faces and edges throughout the mesh.
The faces should be aligned with the axis of animation, as doing so helps prevent the faces from distorting and reduces the possibility of having shading artifacts. It is helpful to think of the faces as a somewhat solid, non-bendable plane so as to not get caught in trying to understand the intricacies and complexities of a fully deformable mesh.
The image below exhibits how faces that are deformed against the flow, the image on the left, will no longer be planar resulting in a triangulation of a flat face. This is result in unwanted artifacts in the renders and generally bad topology.
This is by no means all that there is to be said about topology, which is why I will be writing further and going more in-depth about this topic along with more Blender-related content.
Resources
· https://web.archive.org/web/20191025214321/https://www.cgmascot.com/design/surface-flow-matters/
· Vaughn, W. C. (2018). Topology workbook: Volume 01. Hickory Nut Publishing.