Inspired by my years of caring for pet rats I modeled, sculpted, and textured a model of a typical pet rat as the main project for MODL 302. Students chose an animal and this project guided them through typical modeling stages of blocking out a model, sculpting, retopologizing, sculpting details, and building textures. The main challenge was the need to strictly adhere to a process, which meant committing to certain aspects of the model before moving on to further steps. Students were asked to make an environment for their animals, and I spent a great deal of time modeling the cage and other objects based on the exact cage and environment in which my rats lived.
Case Study
This assignment was designed to guide students through typical modeling stages, and so it is the perfect portfolio piece to discuss the modeling process. The model generally progresses in fidelity throughout the process. The stages outlined below are what I went through to generate my model, but not all of these steps are always necessary, and there are many other processes that can be integrated into the modeling pipeline to produce more life-like renders.
Reference Materials
The first stage for most projects, even when modeling fictional objects, is gathering a good reference material collection. Before searching for images, I clarified the kind of rat I wanted to model. I wanted to model a typical pet rat, the Long-Evans Rat, or simply the hooded rat. I avoided images of other rat breeds, such as those often treated as vermin. I looked for a diversity of images, which showed the rat from many different angles and in many different positions. I also looked for drawings of rat skeletons and musculature, as these helped me understand the structure of my subject matter in a more fundamental way.
Block-Out
Once I found good references, I could finally start modeling. I used Blender for most modeling on this project. The block-out starts as simply as possible. I scaled and moved primitives around to try to match my reference materials. Primitives are the usual building blocks for 3D models and include the cube, sphere, cylinder, cone, plane, and torus. Spheres and cylinders were most useful for blocking out the rat; I could manipulate cylinders to appear as legs, a body, and a tail, while I often used spheres to block out joints. I used mirroring to ensure that the rat had bilateral symmetry. I continued to work on the model in an iterative matter, adding and editing primitives until sculpting became necessary for the model to more closely match my reference materials.
Sculpt
The process of blocking out usually does not result in an accurate model. To make an accurate model, especially for organic objects, sculpting is necessary. This process is analogous to using tools to sculpt clay. I used the tools available in Blender to push and pull vertices until the rat began to take shape and appear realistic. This stage is sometimes called a concept sculpt, as it is the stage where the general shape of the model is established but a lot of detailed work remains.
Retopologize
One of the most important guidelines in 3D modeling is for the topology to be constructed of quad polygons. This means that the surface of the model is made up of rectangles. Ideally, these rectangles are similar in size and are arranged in a logical and orderly manner. The process of retopologizing is the process of creating new geometry that matches the model but is made up of quad polygons.
Up until the retopologize stage I paid little attention to the model’s topology, and sculpting can generate a lot of unnecessary geometry. I imported the model into Maya and used its retopologize function. Producing good topology is a manual process. Maya made it easy to draw new quad polygons on the existing model. This process is time-consuming, but fairly straightforward, although some challenges can crop up depending on the model. My model required the topology to “bend” at the limbs and presented several puzzles in which it initially seemed impossible to only use quad polygons. After retopologizing, I imported the model back into Blender.
UV Unwrap
The stages after retopologizing involve texturing. 3D models are textured with 2D images, and a process known as UV mapping (the U and V 2D axes map onto the X, Y, and Z 3D axes) transforms the 2D images onto the 3D model. A 3D model must be unwrapped into at least one 2D image, and this cannot be done without “cutting” the surface.
I had to choose where I wanted the model to be cut. I tried to place seams in places that are typically out of view on the model or where seams would naturally appear. Once I designated the seams, Blender did most of the work in generating a UV map. If there are not enough seams, textures can appear distorted, so UV unwrapping often involves trying to balance the number of seams with the amount of distortion.
Detail Sculpt
After the model is retopologized it has considerably fewer vertices so it cannot support fine detail. A model cannot use geometry to represent fine detail, as it would be too complex and difficult to render. Instead, images known as normal maps are used to make “fake” geometry which is much easier to render.
In the detail sculpt stage, I went back to using Blender’s sculpting tools on the retopologized low-fidelity model to sculpt in some of the detail lost through retopologizing and to finalize the general shape of the model. Throughout this process, I made sure I did not add any polygons or significantly change the topology.
Next, I made a copy of the low-fidelity model and continued sculpting, aiming to produce a higher-fidelity model, adding in fine detail, such as the ear and tail textures. These textures involved sculpting with a custom brush.
After finalizing the detail sculpt I generated the normal map, which Blender calculates by comparing the low-fidelity model to the high-fidelity model. Next, I imported the low-fidelity model along with the normal map into Adobe Substance 3D Painter.
Texturing
I used Substance Painter to add more fine detail just as I did in Blender, but I also added color and roughness information. For the fur, I masked the furless areas of the rat and used a custom brush. A lot of the work in Substance Painter proceeds in a similar manner: masking followed by painting textures. I painted the black and white coloring with a basic color brush, but I painted other details like the tail and ears with patterned brushes that also added roughness and normal information.
Once I was satisfied with my texturing, I exported several images from Substance Painter which described different information, such as color, roughness, and normals (which also included normal information imported from Blender). I imported these images back into Blender and textured the rat. The textures were reliably transferred because of the UV map generated earlier.
The Cage
I spent far more time creating the cage environment than the assignment required, and I believe my animal’s environment was more complete and realistic than any other student’s work. The process I used to construct the cage environment was the same as the process I used to create the rat. However, many of the objects in the scene were simpler to produce because they had simpler geometry and were less standardized than the Long-Evans rat. I sculpted few objects, and retopologizing was simpler or not necessary. However, I was insistent on matching the exact cage my rats used, and this took a considerable amount of time.
