# Voxel-Based Digital Twin Framework for Earthwork Construction
## 4 Implementation of the Proposed System
### Graphical Simulation Environment for Model-Equipment Interaction
#### 4.1.3 Model Integration in Platform
Figure 12: Comparison results between virtual and actual earthwork entities. (**a**) Volume comparison, and (**b**) activities comparison. ### Operational-Level Voxel-Based Progress Monitoring

In this scenario, the earthwork operational-level progress is monitored using a voxel-to-voxel comparison. The demonstration steps are as follows: (i) data collection, (ii) twin model creation, (iii) alignment of as-planned and as-built models, and (iv) progress visualization and quantification. #### 4.2.1 As-Planned and As-Built Model Creation

The digital twin models include both as-planned and as-built models. Both of these models are created in a voxel-based representation. The as-planned models are created using original ground data, geotechnical data, and design data. On the other hand, as-built models are created using original ground data and current state data. These models are regularly aligned and compared for progress visualization and quantification. For demonstration, firstly, the coordinate system was first set up. Site calibration was performed by using the total station survey equipment. Then, the site coordinate system was developed from four nationally authorized reference points near the competition field. The coordinate system was calibrated to the GRS80 (Korean 2000/Central Belt 2010) and the Geoid KN13. Then, the earthwork site, measuring 105 m \(\times\) 35 m, was scanned with a camera mounted on a UAV, as shown in Figure 13a. Autodesk Civil 3D was used to convert the scanned data into a TIN surface. At the same time, geotechnical investigations, such as boreholes, were conducted to obtain the site's geotechnical information. Additionally, the design trench model was developed and voxelized accordingly (Figure 13b,c). To generate the TIN surface, the point cloud data after pre-processing was imported into Autodesk Civil 3D. The Surface Generation from Points function was used to create a TIN surface of the ground. This workflow inside Autodesk Civil 3D, while not fully automated through application programming interface (API), utilizes semi-automated native functions. Additionally, the geotechnical module was used for the creation of geotechnical boreholes, geotechnical surfaces, and solids. The design model was also created using Autodesk Civil 3D native functions. Figure 13: (**a**) Ground model, (**b**) target model, (**c**) voxelized model, (**d**) voxel-based planning for earthwork construction, (**e**) model update at Time-1, and (**f**) model update at Time-n (adopted from [25]). After the voxel-based as-planned model was developed, the model was divided into different sections for construction planning, and as-built data was captured accordingly (Figure 13d). During the construction stage, the planned voxels were removed, and the model was updated to represent the current state of information. Figure 13e represents the earthwork status after the data was collected at Time-1. Similarly, the data was collected at different intervals, and the model was updated accordingly to represent the current state of information. Figure 13f represents the final model, depicting the as-planned target and as-built target model. #### 4.2.2 Progress Visualization and Quantification

The models were integrated for the visualization and quantitative analysis during construction. The as-built model was compared with the as-planned model at different times, while the target model was shown to the operator and project managers throughout construction. The ground and target models are represented using surfaces, and the as-planned vs. as-built models are represented with voxels. For progress monitoring, the as-built voxel model was noted at different times, and the quantity of excavated voxels was determined. The actual excavated voxel quantities were compared with the as-planned excavation. In this way, earthwork progress was monitored using voxel excavation. On the other hand, productivity was calculated using the following: (i) the excavated voxel data and (ii) the time taken for excavation.