# Advanced Scanning Technology for Volume Change Measurement of Residual Soil
## 4 Proposed Soil Volume Change Measurement Procedures  
Due to the irregularities of a soil specimen during drying, a three-dimensional (3D) scanner was used to capture a precise and accurate 360\({}^{\circ}\) view of the soil specimen. A Matter and Form Scanner with the optics of a high-definition sensor and two Class 1 eye-safe lasers with a scanning accuracy of within \(\pm 0.1\) mm was utilized in the 3D scanning test. The 3D scanner requires MFStudio software v2, which can be downloaded from [[https://www.matterandform.net/pages/v2](https://www.matterandform.net/pages/v2)]([https://www.matterandform.net/pages/v2](https://www.matterandform.net/pages/v2)) (accessed on 21 November 2024). Prior to the commencement of the scanning process, the 3D scanner needs to be calibrated, and a calibrating card should be placed on the 3D scanner for proper calibration, as shown in Figure 2. When the 3D scanner is moved or the lighting situation changes substantially, it is advised that it be calibrated. The MeshLab and Meshmixer software are available for download at [[http://www.meshlab.net/#download](http://www.meshlab.net/#download)]([http://www.meshlab.net/#download](http://www.meshlab.net/#download)) (accessed on 19 November 2024) and [[http://www.meshmixer.com/download.html](http://www.meshmixer.com/download.html)]([http://www.meshmixer.com/download.html](http://www.meshmixer.com/download.html)) (accessed on 19 November 2024), respectively. MeshLab software is required for meshing and trimming cloud points and measuring the volume of the solid soil specimen. Meanwhile, the Meshmixer software is necessary to convert the cloud point into a solid soil specimen. The initial stage in 3D scanning soil specimens in a shrinkage test was to place a soil specimen covered in plastic film on the scanner turntable. Prior to scanning, the following criteria should be met. 1. The bottom surface of the soil specimen is flat, as the surface will not be captured in scanning and is assumed to be flat when editing the cloud point. 2. The plastic film has no fines or stains, especially around the circumference of the soil specimen. The option 'Laser 1' in the MFstudio software should be selected for greater accuracy of scanning. To achieve great accuracy in the scanning process, the following settings should be used:  
1. For a good set of laser lines, the geometry should be set to 60% or adjusted according to the lighting changes in the environment. 2. Texture settings should be set to 60% for optimal color capture exposure, and texture capture should be turned off. Otherwise, the settings should be adjusted to match the soil specimen's color and texture. 3. If the height of the soil specimen is different, adjust the vertical scan path accordingly. 4. For scanning a soil specimen with a height of 30 mm, the vertical scan path should be set to two bars. If the height of the soil specimen is different, the vertical scan path should be modified accordingly. 5. The horizontal scan path should be increased to 100% to scan the entire soil specimen in 360\({}^{\circ}\). After adjusting to the required settings, the quick scan that generally takes about 4 min should be carried out with the above settings. When the scanning is completed,  
Figure 2: Initial calibration of the 3D scanner. any unwanted points of the point cloud may be cleaned using the editing tools. Editing the point cloud with a brush cleaning tool is advised for accuracy. Figure 3 shows the point cloud of a soil specimen after editing in MFstudio. The file should be exported using 'Export' under the file menu and saved as XYZ files. Then, the 'Import Mesh' under the file menu should be chosen by opening the previous XYZ file in the MeshLab software. The point cloud of a soil specimen will appear, as shown in Figure 4. Under the filter's 'Normals, Curvatures and Orientation' menu, the 'Compute normals for sets' should be selected, and an appeared pop-up box should be closed by clicking 'Apply' with the default setting.