General principles

Anleitung für den perfekten 3D Scan

Part I – General Principles

This document is a guide for anyone new to 3D scanning. The advice contained herein provides general guidelines for optimizing scan results obtained with a 3D scanner. These tips refer to the technology used by ScanXpert: active stereo vision 3D scanning. Therefore, they are generally applicable to all 3D scanners in the same category, although some are specifically tailored to ScanXpert.

Structured Light Technology

Active stereo vision structured-light technology is an optical 3D scanning method for capturing the geometry of a physical object. A video projector illuminates the object with various shaped patterns that encode its different spatial positions (Fig. 1).

Two cameras, in a stereo configuration, store the images of the scanned part and the software processes them to generate two coded images (see Fig. 2).

Ein Bereichsbild wird durch Triangulation erfasst. Das Bereichsbild (Abb. 3) ist eine Art Bild, das die 3D-Koordinaten der Objektoberfläche enthält.

3D model generation

To obtain a complete 3D model, the entire area must be captured in different views, which must then be aligned and converted into a mesh of triangles, the digital model (see Figure 4).

TIPP! Proper optical alignment and calibration ensure accurate 3D model generation. These setup steps are required the first time you use the 3D scanner and subsequently only when you change the work area, as described in the quick start guide (see Fig. 5). It is strongly recommended that you follow the quick start guide step by step.

Optimal scans

To obtain an optimal 3D reconstruction, factors that can influence the outcome of the process must be taken into account:

1. the ambient light;
2. the object characteristics such as material, color and shape;
3. the background.

Ambient light

The ideal ambient light for using the 3D scanner is obtained in a room with normal daylight, where the only artificial light is generated by the scanner's projector (see Fig. 6).

It is recommended to use homogeneous light of medium intensity. It should not shine directly on the scene (see Fig. 7) or on the 3D scanner (see Fig. 8).

It is equally important that no shadow is projected onto the object (see Fig. 9).

Direct sunlight can cause problems if it interferes with the projector light. It's best to avoid using the scanner in rooms where sunlight shines directly onto the object being scanned. Controlled ambient lighting is crucial to prevent suboptimal scanning results. Here are some errors that can occur due to poor lighting:

1. Waves caused by light reflected off the object
   (see Fig. 10);
2. Roughness on the scan surface caused by overexposure (see Figure 11);
3. A scan with an orange peel effect, referred to as "noise" when the projector light is lacking compared to the ambient light (see Fig. 12);
4. In the worst case, a scan with many missing areas results in holes on the surface of the digital model (see Fig. 13).

The use of the 3D scanner in outdoor environments is not recommended; use at night may be possible.

TIP! The exposure time, which controls the amount of light absorbed by the cameras, is preset in the IDEA software. In extreme cases where ambient light is a problem, it is possible to manually adjust the camera exposure time, either decreasing or increasing it to create more favorable conditions.

The following images show an object captured by the cameras under the correct lighting conditions with several exposure values: a lower exposure (see Fig. 14), a normal exposure (see Fig. 15) and a higher exposure (see Fig. 16).

PRO TIP! Changing the exposure time is also useful for capturing very dark details that cannot be achieved with a normal exposure setting (see Figs. 17-18).

Object characteristics

There are materials, colors, and shapes that are perfect for digitization, and others that cause critical errors.

Material

Objects with a uniform, non-reflective, and opaque surface are best for scanning. This is because the light creates high-contrast patterns on the surface. Good examples include chalk, clay, and matte sandblasted surfaces. Shiny, polished, or reflective surfaces produce reflections from the projector light during scanning. Similar problems can arise with transparent or semi-transparent materials. In these materials, the light passes through the object's surface, preventing the formation of patterns. Some of these materials that are not recommended include mirrored surfaces, glass and other transparent surfaces, and glossy and metallic surfaces.

TIP! There are hardly any surfaces that cannot be scanned. To scan an object that presents the difficulties just described, simply spray it with a professional coating spray. The white layer allows for the correct pattern formation on the scanned surface and can be easily removed after scanning without damaging the object. Another option is to use a powder, such as talc.

- Color

There are no color restrictions when scanning the object. However, lighter colors yield better results. It is not recommended to scan a model with a completely black or very dark surface, as the projected light will be absorbed by the object and the cameras will not capture enough data to create the 3D model. In this case, the scans will be noisy (orange peel effect).

TIP! The default setting for the "Surface Color" filter is a medium shade. However, it is possible to change this value and choose a lighter or darker shade. In this way, the filter's threshold can be adjusted to eliminate areas of lesser relevance (see Fig. 19).

PRO TIP! If, after the first scan, the 3D image color does not match the real model or is not good enough (see Fig. 20), it is possible to delete the result and perform a color adjustment (optical setup and scan calibration) (see Fig. 21).

Color calibration depends on the ambient light during the scan. Calibration must be performed optimally before scanning. It is recommended to perform color calibration before starting the scan sequence, as otherwise color differences may occur in the overlapping areas of the 3D scan (see Figs. 22-23).

– Form

The shape of the object can influence the scan output. For complex shapes, special attention must be paid to holes or cavities, hidden surfaces, or undercuts on the object's surface. In these cases, it is recommended to perform a larger number of scans from different angles. Outliers can then be removed using the tools available in the IDEA software. To obtain a clear scan, it is crucial that the object does not deform or move during the scanning process. Any vibration of the object during the scan phase will result in significant waviness and missing parts in the 3D image. A deformed object creates alignment problems, and a flawless 3D model cannot be generated. For these reasons, it is not advisable to scan animated objects such as body parts or other objects that can be easily bent or whose shape changes easily, like an extremely soft shoe sole.

TIP! To achieve the best positions for capturing the entire object surface, both the object and the scanner can be moved. It is recommended to utilize the tripod's capabilities. Please note that the correct distance between the projector and the model is important. You can check the correct distance in the software using LIVE mode (with the yellow crosshairs) (see Figs. 24-26).

It is recommended to utilize the tripod's capabilities. Note that the distance between the projector and the model is crucial. The correct distance can be easily checked in the IDEA software using LIVE mode (with the yellow crosshairs) (see Fig. 27).

- Background

The technology used by Scan in a Box enables selective capture of the object. External elements (see Fig. 28) such as the background of the scene or the work surface are excluded from the scan of the object.

In cases where the background is a similar color to the object, some external points may be detected (see Fig. 29). In this case, a manual selection tool or an automatic selection and cleaning tool in the IDEA software can be used to remove these points.

TIP! A work surface with high contrast to the object's surface can achieve optimal results. It is recommended to use a dark, opaque surface such as a black mat as the working plane (see Fig. 30).