If you are encountering problems with the accuracy of the 3D data when using a 3D scanner, there is a chance that the scanner wasn’t calibrated properly. Calibration is perhaps the most important part of setting up a 3D scanner. A good calibration is the key prerequisite for capturing accurate 3D scan data.
The calibration process is important because this is where the scanner determines its environmental conditions such as its position, rotation and behavior in relation to the scan object. The process involves calibrating the scanner’s field of view (FOV), the observable area that the 3D scanner is able to capture from a specific distance. The scanner uses its cameras to define its field of view.
Caption: This diagram illustrates the field of view of a 3D scanner. The Center Depth of Focus is where the scanner is the most focused and this is where the scan object is placed. The Z-Near is the closest distance that the scanner can scan while still in focus. In contrast, the Z-Far is the furthest distance that the scanner can scan while still in focus.
A scanner calibration defines the conversion from 2D images into 3D geometry. During the calibration process, the operator uses the scanner to take calibration images with a calibration plate to aid the scanner in mapping out the positioning of the scanner's optics in 3D space. A good calibration is one that will provide the 3D scanner with an accurate representation of the field of view.
Caption: An example of a calibration plate used for calibrating a white light 3D scanner.
Things to Remember When Calibrating a Scanner
- While taking calibration images during the process, the calibration plate must remain absolutely still as it will affect the accuracy of the scanner calibration. It is best not to hold the calibration plate by hand if possible. For the calibration plate to remain still, it can lean against an object when taking calibration images.
- A scanner calibration is good for a specific field of view. If you are scanning a smaller or larger object that requires a different field of view, you would need to recalibrate the scanner again. In this case, you might also need to use a calibration plate of a different size and/or use camera lenses of a different focal length.
- Using a high accuracy calibration plate will have a direct impact on the accuracy of your scan results. If accuracy is important for your scan project, purchase professionally made calibration boards from your 3D scanner supplier.
- Poor calibration produces inaccurate 3D scans. When calibrating for the first time, try not to rush the process. It may take some practice to achieve the desired calibration accuracy.
- After calibrating the scanner, you can check the accuracy of the 3D scanner by scanning an object of known measurement. If you are interested in this process, please read the blog post: The Importance of Checking the Accuracy of Your 3D Scanner
Do you have any questions related to 3D scanner calibration? Please post in the comments section.
This blog post was previously posted on Tue, May 29, 2012 on 3D3 Solutions blog. LMI Technologies acquired 3D3 Solutions on May 1, 2013. 3D3 Solutions website will be redirected to LMI Technologies website.
Posted by Thomas Tong