Accuracy and resolution in 3D scanning

Contents: WHAT IS ACCURACY AND RESOLUTION | HOW TO UNDERSTAND THE ACCURACY OF A 3D SCANNER | RESOLUTION IN 3D SCANNING | RELATIONSHIP BETWEEN RESOLUTION AND ACCURACY | SUMMARY

WHAT IS ACCURACY AND RESOLUTION?

In the world of 3D scanning, the terms "accuracy" and "resolution" are ranked among the most important parameters. Often these two concepts are confused or understood as one. In this article, we will take a closer look at what each term means and how it is important. As a result, these key parameters are very closely related. However, it is important to understand these terms separately when choosing a 3D scanner.

HOW TO UNDERSTAND THE ACCURACY OF A 3D SCANNER?

The accuracy of the device, in this case the 3D scanner, is determined by the manufacturer. Based on the technology used, the manufacturer is able to determine with what accuracy a given 3D scanner is able to create a 3D scan in digital form. The resulting accuracy is based on the technology used in the device and the way the device detects the given object. The user does not need to know which cameras and components the device uses, as the manufacturer guarantees the resulting accuracy. When exploring accuracies, you may come across three possible names. Different manufacturers list different, seemingly interchangeable designations for accuracy. In reality, however, accuracy is viewed from a different angle in each of them. We highly recommend paying extra attention to these characteristics when choosing a device. We may encounter:

• Accuracy from (Flyers and catalogs most often state the accuracy from. Therefore, a scanned 3D model can be created on a computer after a 3D scan with an error from the specified value. However, we are not able to determine from this accuracy the worst error with which the given part can be scanned.)
• Single frame accuracy (A 3D scanner creates a 3D model of a part from one view. The specified accuracy guarantees that one of these images will be created with the specified accuracy. However, it takes X images to scan the entire part. What will the resulting accuracy be when all the images are merged into one whole? From this method accuracy determination it is not possible to determine the resulting accuracy of the scan.)
• Volumetric accuracy (The manufacturer carries out 3D scanning tests. In a certain space, he tries to scan the artifact and thus find out the maximum possible deviations. After the tests, he is therefore able to guarantee that the permissible deviation for the given size is X.xx mm. The resulting scan can therefore vary in accuracy up to X etc.)

RESOLUTION IN 3D SCANNING

The most common output from a 3D scanner is a cloud of points or a polygon network (it forms the surface of the scanned object).

• For a point cloud, the term resolution means how far apart the created points are in space.
• The resolution of the polygon mesh determines how large the triangles that make up the final 3D scan will be. According to the specified resolution, the scanning program creates a polygon network so that each triangle has an edge length of X mm.

Thanks to the resolution, we are therefore able to determine how detailed a scan we want to create. The larger the resolution value, the fewer triangles will appear on the 3D scan. The smaller the resolution value we set, the more triangles the final scan will have, and the more detailed it will be.

The resolution value significantly affects the length of the scan, the time of calculations and the resulting size of the 3D scan in MB. We recommend choosing a resolution so that the necessary details can be reliably seen on the scan, but it is not overly fine. How to do it? Let's see what smallest detail we need to capture on the piece. If, for example, it were a radius of R4, then at least 4 triangles should be created on the surface of the radius for a quality representation. So radius 4mm : 4 triangles = 1mm resolution.

RELATIONSHIP BETWEEN RESOLUTION AND ACCURACY

So, in general, the values ​​"accuracy" and "resolution" are not related. Both parameters express a different characteristic of the 3D scan. However, if we set the wrong resolution (too few triangles), the resulting 3D scan will be less detailed and the accuracy of the 3D scan will also deteriorate. However, the vertices of the triangles lie within the specified accuracy of the device on the surface of the scanned object. Only due to the small number of triangles, the detail is degraded and there are large deviations from the surface. However, this is not due to the inaccuracy of the 3D scanner.

Which 3D scan is more accurate? None. The accuracy is the same, only the resolution is different.

SUMMARY

As we described in the article, the accuracy of the resulting 3D scan is conditioned by external conditions and compliance with the correct 3D scanning methodology. The reduction in accuracy is always due to operator error. For example, we misplace position points, the part vibrates during 3D scanning (position points are around it) and more.

The resolution affects the number of triangles that make up the resulting 3D scan. A poorly chosen resolution can indirectly affect the accuracy of the resulting 3D scan.