Three-dimensional volume measurement of stockpile based on machine vision technology

1. Introduction: In the industrial field, industrial production requires the stacking of various mineral raw materials, such as coal, sand, gravel, rare earths and ores, thus forming a large number of material piles of various shapes. Real-time and accurate estimation of the volume (earth volume) of these material piles is an important data guarantee to ensure the normal production. There are currently two main methods: 1) Use a mobile 3D laser scanner: A manual handheld 3D laser scanner can be used to perform a 360° scan of the material pile in a mobile non-contact measurement mode to collect 3D data, and then the data is 3D modeled by professional analysis and processing software, restored to the real material pile topography, and then the volume is calculated. Advantages: The measurement results are relatively accurate and do not require the position of the material pile to be fixed; Disadvantages: It is labor-intensive and difficult to be real-time, and the 3D scanner is expensive; Applicable: Fields that require very accurate volume estimation and high budgets;

Figure 1. Volume measurement with a handheld 3D laser scanner (from a certain manufacturer) 2) Use multi-point fixed laser ranging: multiple laser ranging scanners can be installed around a fixed material pile, and the local elevation information of each surface of the material pile can be collected. Combined with the installation position of the scanner, the overall 3D estimation modeling of the material pile can be performed, and the volume of the material pit can be estimated. Advantages: The laser ranging scanner is low-priced, and real-time measurement does not require human intervention; Disadvantages: The estimated volume error is large, and the material pile position needs to be fixed; Applicable: Fields where the measurement error requirements are not very precise and the budget is limited;

Figure 2 Multi-point fixed laser ranging volume measurement (Danweisi software)

2. Material pile modeling: This article mainly introduces the multi-point fixed laser ranging method. It uses Danweisi 3D modeling software to obtain the surface point cloud of the material pile from the multi-point fixed laser rangefinder, and then performs 3D modeling and volume calculation based on the point cloud.

Figure 3. Steps for stockpile modeling 1) Laser ranging hardware: Obtain the stockpile contour information. The installation method is shown in Figure 2.

Figure 4 Laser distance measurement hardware (partner of Danweisi) 2) Point cloud modeling: Read point cloud information from the distance measurement hardware to start stockpile modeling

Figure 5 3D point cloud (Danweisi software) 3) 3D modeling: 3D segmentation/contour method for stockpile modeling, volume and surface area calculation

Figure 6 Three-dimensional modeling (triangulation) (Danweisi software)

Figure 7 3D modeling (outline) (Danweisi software)

3. Real-time transmission: The system can transmit the surface area, volume and three-dimensional appearance of the material pile to the server through wired/wireless network in real time for access by various information systems.

Figure 8 Real-time data (Danweisi software)

4. Error estimation: As mentioned above, the area and volume of the pile calculated by multi-point fixed laser ranging method have large errors, as follows: 1) The error size is proportional to the coverage of the laser ranging on the pile surface. That is, to improve accuracy, you can add fixed laser rangefinders to improve coverage and accuracy.

2) According to actual engineering experience, the volume of the stockpile calculated by 3D modeling differs from the actual volume by about 1%, but this data can only describe the situation of part of the project, and the actual situation requires specific analysis.