The 3D scanning is a now widespread technique in almost all industrial and commercial sectors, but also in art, architecture, and in the medical sector.

The merit of this widespread diffusion lies in the fact that 3D scanners are increasingly easier to use even for non-expert users.

Furthermore, 3D scanning technologies allow to speed up most of the production activities and make possible previously unthinkable processes or interventions.

Nevertheless, some problems can always occur during the 3D scanning phase , which can be overcome with easy tricks.

In this article we want to examine the various difficulties that can arise during a 3D scanning session and reveal the tricks and techniques to solve them, making 3D scanning possible for any type of application.

 

HOW TO PERFORM A 3D SCAN IN ANY SITUATION

If you have ever tried your hand at a 3D scan using optical 3D scanners, you will surely have found yourself faced with some questions including:

  1. How to scan glossy or black surfaces ?
  2. How to scan cavities ?
  3. How to scan thin objects like foil?
  4. How to behave in case of loss of alignment with both markers and without markers?
  5. How to exclude some areas of the scene from 3D scanning?
  6. How to automatically or manually align two 3D scans of different parts of the same piece?

 

In all these situations it is still possible to perform a quality 3D scan but with due precautions, techniques and tools. Let's analyze each point individually.

 

1. 3D SCANNING OF GLOSSY OR BLACK SURFACES

With shiny or black or shiny and black surfaces, most optical 3D scanners have difficulty detecting 3D geometry correctly, as light is reflected excessively from surfaces or completely absorbed.

What can therefore occur is a non-acquisition or a partial acquisition of the objects.

To overcome this difficulty, first of all professional and advanced 3D scanners can be used, which allow manual and / or automatic adjustment of some optical 3D scanning parameters such as exposure .

The 3D scanners that allow this adjustment can be either laser 3D scanners , such as Shining 3D's FreeScan series , or structured light 3D scanners , such as Shining 3D's EinScan Pro series , or with new technological advances, it is It is possible to have hybrid 3D scanners, which combine laser and structured light 3D scanning technologies in a single tool, such as the Shining 3D EinScan HX and H series 3D scanners .

In general, however, 3D laser scanners are often the most suitable for surfaces with different optical characteristics.

Some 3D scanners are able to self-adjust the exposure in real time according to the surface to be scanned; others allow manual adjustment, which in this case must be low for light surfaces and high for dark surfaces.

If there are both light and dark surfaces in an object at the same time, automatic exposure is the best solution.

In those cases in which the 3D scanner is not equipped with adjustable optical parameters, or if even by adjusting the parameters it is not possible to acquire the surface, it will be possible to perform the 3D scan by opacification with special powders, some of which are evanescent and do not leave no trace on the surfaces. One such product is Aesub Blue spray.

2. 3D SCANNING OF OBJECTS WITH CAVITIES

In the event that the objects to be scanned have holes and cavities, it will not always be possible to 3D scan even the cavities themselves, since normally only the surfaces that the laser or structured light of the 3D scanner can reach are scannable.

To scan cavities totally internal to objects, 3D scanning can be replaced with computed tomography (CT), if instead the cavities have an outlet on the external surface, you can try to scan them as far as the light reaches.

Some 3D laser scanners, such as Shining 3D's FreeScan X7, are equipped with a special laser blade capable of going deeper into cavities and through which it is also possible to acquire some narrow holes.

3. 3D SCANNING OF THIN OBJECTS

In the case of thin objects such as foils, the difficulty in scanning lies in the fact that around the edges of the thin wall the 3D scan can be very noisy or even the edges may not be scanned at all. This is due to the fact that light reflects unpredictably around a very thin edge, resulting in clusters, holes and errors.

In this case, the adjustment of the optical scanning parameters and the possibility of using a 3D laser scanner can overcome this drawback or at least limit it.
In general we can say that the more professional and metrological the 3D laser scanner is, the more successful the 3D scanning of thin objects can be.

However, even in the event of errors or clusters near the edges, the exact geometry of the sheet can always be reconstructed thanks to the best performing 3D modeling and mesh editing software, which can be combined with any 3D scanner.

 

4. WHAT TO DO IN CASE OF MISALIGNMENT DURING A 3D SCAN

If you use automatic portable or even tabletop 3D scanners, 3D scanning takes place in real time through the automatic alignment of each scan frame on the previous one, using physical markers, or using geometric or color characteristics.

In the event that real-time alignment is momentarily lost during 3D scanning, the 3D scanner will either no longer acquire 3D data, or will misalign it.

In both cases there is an effective solution to remedy the problem.

In the event of temporary loss of alignment in the presence of markers, simply reposition the 3D scanner so that it will re-acquire a certain number of previously acquired markers. In this case the alignment will be restored and the 3D scanning can continue without problems. Generally, in order not to lose alignment, it is necessary to position the markers so that there are always at least 4 markers in common between one 3D scan frame and the next.

In case of loss of alignment in the absence of markers, the 3D scanner must be repositioned on a previously acquired geometry, so that it can be recognized and the alignment restored. If this fails automatically, in some 3D scanners it is possible to select an option through which the frame from which to restart can be selected to regenerate the alignment.

Generally, in order not to lose alignment in the absence of markers, it is necessary to move the 3D scanner so that there is always a sufficient overlap area between one 3D scan frame and the next.

In any case, if misaligned or misaligned frames are recorded during the misalignment, with most 3D scanners you can select and delete them, so that the 3D scanning continues without problems.

5. 3D SCANNING EXCLUDING SOME AREAS OF THE SCENE

In case you want to exclude a part of the scene from 3D scanning, such as when you want to eliminate the table on which an object is placed, some 3D scanners and some 3D software allow you to do this automatically by defining work plans that delimit the region of space that you want to scan. These cutting planes are very useful for isolating the objects you want to view within the 3D scan.

6. THE ALIGNMENT OF DIFFERENT 3D SCANS OF THE SAME OBJECT

In some situations it may be useful to scan the same object from two different perspectives and then combine the two 3D scans to form a single 3D model. In this case the alignment can be done either by target or by geometric characteristics.

This operation requires the use of software for mesh registration and can be performed by selecting any targets in common on the two parts of the object, or parts with overlapping geometry and aligning them using best fit algorithms.