3D modeling
In 3D computer graphics, 3D modeling is the process of developing a mathematical coordinate-based representation of a surface of an object in three dimensions via specialized software by manipulating edges, vertices, and polygons in a simulated 3D space.
Three-dimensional models represent a physical body using a collection of points in 3D space, connected by various geometric entities such as triangles, lines, curved surfaces, etc. Being a collection of data, 3D models can be created manually, algorithmically, or by scanning. Their surfaces may be further defined with texture mapping.
Outline
The product is called a 3D model, while someone who works with 3D models may be referred to as a 3D artist or a 3D modeler.A 3D model can also be displayed as a two-dimensional image through a process called 3D rendering or used in a computer simulation of physical phenomena.
3D models may be created automatically or manually. The manual modeling process of preparing geometric data for 3D computer graphics is similar to plastic arts such as sculpting. The 3D model can be physically created using 3D printing devices that form 2D layers of the model with three-dimensional material, one layer at a time. Without a 3D model, a 3D print is not possible.
3D modeling software is a class of 3D computer graphics software used to produce 3D models. Individual programs of this class are called modeling applications.
History
3D models are now widely used anywhere in 3D graphics and CAD but their history predates the widespread use of 3D graphics on personal computers.In the past, many computer games used pre-rendered images of 3D models as sprites before computers could render them in real-time. The designer can then see the model in various directions and views, this can help the designer see if the object is created as intended to compared to their original vision. Seeing the design this way can help the designer or company figure out changes or improvements needed to the product. Simple wireframes were the first versions of early 3D models, which were mainly used to view construction plans and mechanical parts. Better graphics hardware and software allowed for the creation of solid and surface models in the 1970s and 1980s, giving designers a more realistic and clear representation of physical objects. By the 1990s, parametric modeling became popular, letting designers change a model by changing its basic parameters instead of redrawing it from scratch. Thanks to virtual reality, artificial intelligence and generative design tools, 3D modeling today goes past engineering and is influencing fields like animation, gaming, product design and cinema.
Representation
Almost all 3D models can be divided into two categories:- Solid – These models define the volume of the object they represent. Solid models are mostly used for engineering and medical simulations, and are usually built with constructive solid geometry.
- Shell or boundary – These models represent the surface, i.e., the boundary of the object, not its volume. Almost all visual models used in games and film are shell models.
Shell models must be manifold to be meaningful as a real object. For example, in a shell model of a cube, all six sides must be connected with no gaps in the edges or the corners. Polygonal meshes are by far the most common representation. Level sets are a useful representation for deforming surfaces that undergo many topological changes, such as fluids.
The process of transforming representations of objects, such as the middle point coordinate of a sphere and a point on its circumference, into a polygon representation of a sphere is called tessellation. This step is used in polygon-based rendering, where objects are broken down from abstract representations such as spheres, cones etc., to so-called meshes, which are nets of interconnected triangles. Meshes of triangles are popular as they have proven to be easy to rasterize. Polygon representations are not used in all rendering techniques, and in these cases the tessellation step is not included in the transition from abstract representation to rendered scene.
Process
There are four popular ways to represent a model:- Parametric modeling – A feature-based parametric modeling structure, which relies on parent-child relationships between features, allowing for a number of methods for building specific models in the context of mechanical CAD systems.
- Polygonal modeling – Points in 3D space, called vertices, are connected by line segments to form a polygon mesh. The vast majority of 3D models today are built as textured polygonal models because they are flexible and because computers can render them so quickly. However, polygons are planar and can only approximate curved surfaces using many polygons.
- Curve modeling – Surfaces are defined by curves, which are influenced by weighted control points. The curve follows the points. Increasing the weight for a point pulls the curve closer to that point. Curve types include nonuniform rational B-spline, splines, patches, and geometric primitives.
- Digital sculpting – There are three types of digital sculpting: Displacement, which is the most widely used among applications at this moment, uses a dense model and stores new locations for the vertex positions through use of an image map that stores the adjusted locations. Volumetric, loosely based on voxels, has similar capabilities as displacement but does not suffer from polygon stretching when there are not enough polygons in a region to achieve a deformation. Dynamic tessellation, which is similar to voxel, divides the surface using triangulation to maintain a smooth surface and allow finer details. These methods allow for artistic exploration as the model has new topology created over it once the models form and possibly details have been sculpted. The new mesh usually has the original high-resolution mesh information transferred into displacement data or normal map data if it is for a game engine.
- Constructive solid geometry
- Implicit surfaces
- Subdivision surfaces
3D models can also be created using the technique of Photogrammetry with dedicated programs such as RealityCapture, Metashape and 3DF Zephyr. Cleanup and further processing can be performed with applications such as MeshLab, the GigaMesh Software Framework, netfabb or MeshMixer. Photogrammetry creates models using algorithms to interpret the shape and texture of real-world objects and environments based on photographs taken from many angles of the subject.
Complex materials such as blowing sand, clouds, and liquid sprays are modeled with particle systems, and are a mass of 3D coordinates which have either points, polygons, texture splats or sprites assigned to them.
3D modeling software
There are a variety of 3D modeling programs that can be used in the industries of engineering, interior design, film and others. Each 3D modeling software has specific capabilities and can be utilized to fulfill demands for the industry.G-code
Many programs include export options to form a g-code, applicable to additive or subtractive manufacturing machinery. G-code works with automated technology to form a real-world rendition of 3D models. This code is a specific set of instructions to carry out steps of a product's manufacturing.Human models
The first widely available commercial application of human virtual models appeared in 1998 on the Lands' End web site. The human virtual models were created by the company My Virtual Mode Inc. and enabled users to create a model of themselves and try on 3D clothing. There are several modern programs that allow for the creation of virtual human models.3D clothing
The development of cloth simulation software such as Marvelous Designer, CLO3D and Optitex, has enabled artists and fashion designers to model dynamic 3D clothing on the computer.Dynamic 3D clothing is used for virtual fashion catalogs, as well as for dressing 3D characters for video games, 3D animation movies, for digital doubles in movies, as a creation tool for digital fashion brands, as well as for making clothes for avatars in virtual worlds such as SecondLife.
Comparison with 2D methods
3D photorealistic effects are often achieved without wire-frame modeling and are sometimes indistinguishable in the final form. Some graphic art software includes filters that can be applied to 2D vector graphics or 2D raster graphics on transparent layers.Advantages of wireframe 3D modeling over exclusively 2D methods include:
- Flexibility, ability to change angles or animate images with quicker rendering of the changes;
- Ease of rendering, automatic calculation and rendering photorealistic effects rather than mentally visualizing or estimating;
- Accurate photorealism, less chance of human error in misplacing, overdoing, or forgetting to include a visual effect.