What is 3d scanning and why it is needed

What is 3d scanning and why it is needed | 2022

Hello, dear visitors to the site! With this post I open a series of articles about 3d scanners and 3d scanning. In this article we will look at what methods of scanning exist, how they differ and where they are used. To begin with let’s understand what 3d scanning is all about.

To begin with, let’s understand what 3d scanning is all about. Imagine that there is a part with a lot of complex surfaces, which an ordinary caliper can not measure, or you will have a long and painful to labor to get the results of the required accuracy. And then you have to get a mathematical model from that data. This is where the 3D scanner comes in. It allows many times less time to obtain a mathematical model suitable for comparison with a reference model. The use of scanning does not end here. 3d scanning is also used to obtain accurate models of complex objects, which can later be used to obtain product prototypes, the construction of new products on the basis of existing ones. They are also used in the film industry, in medicine, in museums, in industrial design and in the entertainment industry, for example, in creating computer games. With three-dimensional scanning it is possible to digitize cultural heritage, archaeological objects, and objects of art. In addition, three-dimensional scanning is widely used in medical prosthetics, in digital archiving, and so on. Now let’s understand what methods of 3d scanning exist.

At the moment there are the following scanning methods:

  1. Contact method.
  2. Non-contact methods:
  • Active method.
  • Passive method.

Areas of application of these methods:

  • Engineering analysis
  • Quality Control &
  • Inspection
  • Packaging Design
  • Digital Archiving
  • Industrial Design
  • Entertainment & Games
  • Accessories Market
  • Reproduction and customization
  • Medical & Orthopedics

Contact method

The basic principle of this method is to surround the object being scanned with a special mechanical device, which is a sensor and is called a stylus. Before scanning begins, a grid is applied to the object, the cell size of which should be minimum in areas of high surface curvature and largest in areas of low curvature. Points are formed where the grid lines intersect. The coordinates of these points are measured with the stylus and entered into the computer. This method is used when manually tracing the surface of the object. The modern development of this method is the use of a special device for scanning. In this case, there is no need to trace and grid the object manually. The stylus moves along the surface of the object and the coordinates of its position are entered into the computer. A three-dimensional model of the scanned object is built on the basis of these coordinates.

The advantages of contact 3D scanning:

simplicity of the process,
independent of lighting conditions,
high-precision scanning of ribbed surfaces and prismatic parts,
compact volume of obtained files.

Disadvantages:

Inability to capture the texture of the object being scanned,
Difficulty or inability to scan objects of large size.

Non-contact methods:

Active method

The active method is based on registering reflected rays from the object being scanned. The source of such rays is the 3d scanner itself. The scanner can irradiate the object with the following types of rays:

– directional light,
– laser,
– ultrasound,
– X-rays.


The principle of this method is based on measuring the distance from the scanner to the points of the object being scanned. These points can be reflective self-adhesive markers. Also widely used is the scanning of optical systems that use modulated or structured illumination. In the case of modulated illumination, the object is illuminated by light pulses that change in a certain way. The camera reads the reflections and receives the appearance of the scanned object from the distortions. In the case of structured illumination, the object is illuminated by a certain “pattern” (grid), according to the distortions of which the camera forms a 3d model. These data are either stored in the scanner memory and then transmitted to a computer, or immediately sent to the computer, where they are processed and build a three-dimensional model. Since 3d scanner at one point in time sees only part of the object, in the process of scanning it is necessary to move the scanning object, or move the scanner itself. Thus, in the end we get a model by stitching together the resulting pieces of the object. In most cases, the scanned piece of the object is displayed immediately on the computer screen. This allows you to check immediately how well the scanning angle is chosen, and to understand how many iterations of the object can be scanned. By choosing the right angles to scan, you can achieve a reduction in scanning by reducing the number of pieces of the object scanned.

The advantages of the active 3d scanning method:

low scanning cost,
Can be used outdoors,
Use in different lighting conditions,
No need to apply a grid on the object,
scanning is done by non-contact technology,
It is possible to scan objects that are inaccessible to other scanning methods.


Disadvantages:

difficulty or inability to scan transparent and mirrored surfaces,
Scanning of small items requires the use of more accurate optics, and therefore more expensive 3d scanners.

Passive method

The passive method uses already existing ambient light. The reflection of this light from the object and is analyzed by 3d scanner. In fact, this method of scanning is either shooting an object with ordinary video cameras in different light conditions and restore them in 3d, or capture the silhouette of the object on a high-contrast background using stereoscopic or “silhouette” cameras.

Result:

Each method is good and attractive in its own way. The choice between these methods should be based on financial considerations, the complexity of the object to be scanned and the accuracy you want to get as a result.