A couple of years ago I wrote an article for Sign & Digital Graphics about the wonders of 3D modeling. As I’m sure you realize, in the world of digital technology things change pretty fast so I thought I’d present a few updates to this exciting new method of creating in-the-round objects as digital files.

The previous article—“3D Breakthroughs,” June 2013, SDG—was a general overview of the technology and included modeling, scanning, carving and printing. In this article we’ll focus a little more on the specifics and terminology. I’ll present the initial steps in creating 3D forms: 3D software for the purpose of generating 3D models from scratch, and 3D scanners for capturing existing 3D models. Look for part two of this two-part series in my “Digital Eye” column in the November issue of Sign & Digital Graphics.

3D Modeling Software

The process of creating 3D objects from scratch begins by building a virtual design in a 3D modeling program. 3D modeling software packages provide the artist with virtual tools for sculpting on a computer. For an online list of available modeling programs, visit https://en.wikipedia.org/wiki/List_of_3D_modeling_software.

Polygons

3D programs divide the surface of a model into polygons. Polygonal modeling is technique for configuring objects by approximating their surfaces using multi-sided shapes (see Figure 1). The polygons are usually triangles, but they can also sometimes be quadrangles (four-sided) or N-Gons (five-or more sides).

3D forms can consist of NURBS (non-uniform rational b-splines) used for very smooth objects that are created using Bezier curves. To form a NURBS surface, the artist draws two or more curves in 3D space, which can be manipulated by moving handles called control vertices along the x, y, or z axis (see Figure 2). The software application interpolates the space between curves and creates a smooth mesh between them. NURBS surfaces have the highest level of mathematical precision, and are therefore most commonly used in modeling for engineering and automotive design.

Surfaces can also include NURMS (non-uniform rational mesh smooth) that are related to polygonal geometry. NURMS use an algorithm to smooth polygon geometry, sort of like a virtual rasp.

3D Components

3D models consist of Vertices. A vertex is the smallest component of a polygon model. It is simply a point in 3D space. By connecting multiple vertices, a polygon model is created. These control points can be manipulated to create the desired shape.

Polygons consist of Faces which are the defining characteristic of a polygonal model. Unlike NURBS surfaces, polygonal meshes are faceted, meaning the surface of the 3D model is comprised of a mesh of hundreds or thousands of geometric faces.

3D models also contain Edges. An edge is any point on the surface of a 3D model where two polygonal faces meet (see Figure 3).

The number of polygons in a mesh is called the poly-count. Polygon density is called resolution. The best 3D models have more polygons where more detail is required—like a character's facial features—and lower densities in less detailed regions of the surface (see Figure 4). Typically, the higher the overall resolution of the mesh, the smoother it will appear when it is finally rendered. Conversely, low-resolution meshes will look faceted or boxy.

The Scene

The 3D form exists within an environment called a Scene (see Figure 5). The scene is composed of three planes: the X is the horizontal plane and is represented by a red line, Y is the vertical plane represented by a green line and Z is the depth plane represented by a blue line. The model can be rotated or moved within any of the three axes so that all sides can be viewed and developed.

Using 3D software can be compared to sculpting, only virtually. The software contains tools for manipulating the shape and surface texture of the 3D model in a multitude of ways (see Figure 6). A 2D concept drawing can be developed into a 3D model and its surfaces can be smoothed. The form can be wrapped with a material (a texture or surface element) and the form can be can be lit with a single or multiple light sources. When completed, the file is rendered and exported into other software for realistic stills, computer animation and of course, imaging to a 3D printer.

3D Scanning

If a solid object already exists, it can be scanned with a 3D scanner. 2D systems create flat digital images with a specific height and width, while 3D systems create digital forms with height width and depth. For a 2D system, depth is missing and flattened within two-dimensional space. In a scan of a photo, for example, depth is perceived from color, shadows and lighting. A 3D scan by comparison, produces an in-the-round 3D shape by measuring and analyzing dimensional information. Although they are different, 2D and 3D systems are not incompatible. Many of today’s 3D scanning devices combine both technologies. For example, some 3D scanners collect color and tonal data and map it to the 3D form.

These devices measure the physical world using a light source (typically lasers or LEDs). Software interprets the captured data into polygon meshes. The common uniting factor of all 3D scanners is that they capture the geometry of physical objects with hundreds, thousands or millions of measurements. A 3D scanner can collect data that can ultimately produce accurate, high-resolution digital 3D models from real-world objects.

Triangulation

Surveyors have been using triangulation to plot maps and build roads for hundreds of years. By analyzing the angles and lengths of a triangle, distances can be calculated. Triangulation is the principle that enables 3D scanning technologies to determine the dimensions and surface geometry of real-world objects (see Figure 7).

3D scanning devices measure the distance and angles between the origin of the light source (usually a laser) and the imager (usually a camera). As the device scans the surface of the object, the distance between the projected light source and the imager creates the base of the triangle. The angle of the projected light bouncing off the object and returning to the imager completes a triangle where the distances are calculated. By applying this principle of triangulation of numerous points on the surface, a digital 3D representation of an object is created. Scanning software assembles the data into an image defined by a polygonal mesh.

Visualization

Current 3D scanning technology is capable of collecting an enormous amount of data from the scanned object’s surface. With this data the software can produce a detailed, high resolution, accurate 3D digital model of the real-world object. This is known as 3D visualization (see Figure 8).

There are many types of 3D scanning technologies on the market today, from commercially used game controllers to industrially designed smart scanning devices. Some 3D scanners are stable and project their laser beam as the object rotates on a turntable and some are hand-held (see Figure 9). There are basically four types of 3D scanning devices:

• Displacement devices use a single point laser beam projection to measure the height, thickness, or position of an object.
• Line Profile devices typically use a projected laser line to create a cross section profile for measuring aspects of an object’s contour. The object rotates under the laser line and creates many profiles that can be combined into a complete 3D shape.
• Snapshot devices use structured light (non-laser) and stereo-vision to generate 3D data. Because Snapshot technology captures so much 3D data at one time, objects need to remain stationary during the scanning process.
• A 3D Sensor is a single device that uses fixed optics, a light source (typically laser) and at least one digital imager to acquire 3D data. Typically, 3D sensors are pre-calibrated and operate in manufacturing facilities as part of an automated production workflow.

Much like the human eye, 3D scanning devices merely collect data and transmit it to a computer with 3D software. The software analyses the data and creates the visualization.

Hopefully this article has shown you a bit about 3D models and how they are either virtually sculpted or scanned. Now you know what a Vertex is, as well as NURBS and an N-Gons. To sum up, 3D models are simply complex geometric shapes with a multitude of little polygonal faces that can be manipulated. While, it's undoubtedly interesting to read about 3D models, it's more exciting and fun to make them yourself. It’s even more fun to print your 3D model to a 3D printer. So tune in to the November issue of Sign & Digital Graphics and get the inside skinny on 3D printing.