The Ultimate Guide for Measurement Accuracy

One concept that comes up repeatedly when talking about 3D scanners is accuracy. How do you understand the concept of accuracy? Does it mean correctness, quality, or authenticity? If you too feel that this concept is a bit vague, then this article is for you.

Here, we will explain accuracy and a concept closely related to it, precision, as well as what affects accuracy when measuring. We will also help you quickly choose a metrology-grade 3D scanner suitable for the accuracy you need.

Accuracy VS Precision VS Volumetric Accuracy

When taking measurements, accuracy and precision are essential, as they indicate the proximity of a measured value to a recognized or established value. These two concepts are crucial in determining the measurement's reliability.

The accuracy is the closeness of the measurement results to the true value. ISO calls this trueness. Alternatively, ISO defines accuracy as a combination of random and systematic errors. For applications such as automotive tuning and industrial manufacturing, accurate data is undoubtedly crucial.

Accuracy test with FreeScan Trak

Precision is also known as repeatable measurement accuracy, which means the degree of stability (conformity) between measured values under the same conditions, measured several times over. Like an athlete shooting at a target, a quality player can consistently hit the center area. The accuracy of the 3D scanner can be compared to the hitting area of a target, and the precision to the stability of the performance of multiple hits.

Accuracy VS Precision

Additionally, there is a volumetric accuracy during alignment. There is a linear cumulative error in the alignment of images during the scanning process, which can be expressed as initial accuracy + cumulative alignment error. It will be introduced in detail in part 3, and how we should eliminate this error.

Factors Affecting Measurement Accuracy

Regardless of the manufacturer or market position, the accuracy of a 3D scanner can fluctuate somewhat due to various factors such as temperature, data integrity, algorithms, and scanning angles. It is important to understand how to prevent deviations in accuracy and obtain the most reliable and accurate 3D data.

1. Temperature

To ensure optimal scanning accuracy, it is crucial to allow the scanner to warm up and maintain a stable temperature. After the temperature stabilizes, calibration should be performed before scanning to achieve the best possible accuracy. This sequence of warming up, stabilizing the temperature, calibrating, and then scanning will yield the most accurate results.

2. Data integrity

The integrity of the data is an important factor affecting accuracy. Incomplete data can lead to inaccurate or distorted results, compromising the overall quality of the 3D information. Therefore, it is important to ensure that the data is complete and authentic to obtain the most accurate results.

3. Algorithm

Algorithms play a vital role in 3D information acquisition, from calibration to data processing. It is a complex set of mathematical equations that ensure the accurate reconstruction of the scanned object. Calibration is also an important part of the process, ensuring the accuracy of the scanner and providing the necessary data for the algorithm to work correctly.

4. Angle of scanning

The angle at which the scanner is positioned relative to the object being scanned is critical to obtaining accurate and complete 3D information. Ideally, the scanner should be positioned as perpendicular to the object as possible. This positioning helps the scanner to extract markers more accurately and thus obtain more accurate 3D information.

Scanning with FreeScan UE

Volumetric Accuracy

Volumetric accuracy is the closeness between the measured value and the true value in a given measurement space. For example, if a device has an accuracy of 0.02 mm and the deviation increases by 0.04 mm per meter, its volumetric accuracy is 0.02 mm + 0.04 mm per meter.

The cumulative error of scanning a larger object is higher. However, such deviations are not negligible and there are scanning methods that can help reduce errors, such as global marking and photogrammetry.

Global markers

Before scanning the point cloud, we can first scan the global markers so that algorithms can optimize accuracy to obtain more precise data, ultimately improving volumetric accuracy.

Photogrammetry

Photogrammetry can enhance the accuracy of global marker data. We can import suitable scale bar files and place matching scale bars near the object before scanning, depending on the size of the scanned object. Generally, photogrammetry is suitable for measuring large parts in industrial applications that require high accuracy. Of the two methods, photogrammetry is considered better than global markers.

Scanning Airplane Models Using Photogrammetry

SHINING 3D Metrology Family

For objects that require high accuracy and with a small size, two models are recommended: AutoScan Inspec and OptimScan 5M Plus. Autoscan Inspec is fully automatic, which provides greater convenience, while OptimScan 5M Plus can handle slightly larger objects than AutoScan Inspec.

High accuracy and high detail

How should we choose from the FreeScan series? If the object we are scanning is large and requires high accuracy, we can choose FreeScan UE Pro, because it is equipped with photogrammetry, which can greatly reduce the error of the alignment process.

FreeScan UE application site

FreeScan UE Pro application site

Finally, Let’s talk about FreeScan Trak. This scanner is different from other scanners in that it does not require markers on the scanned object. If it is difficult to paste markers on some large objects, you can consider this scanner.

Now that you are familiar with what is accuracy, what is precision, and what is volumetric accuracy, you can now think about which scanner is best for you based on the accuracy you need. SHINING 3D is happy to provide one-to-one demonstrations while offering quality solutions.

Talk to the experts today to learn more about 3D scanning technologies and how they can have a lasting impact on your business.