# Path Planning Strategy for Implementing a Machine Control System in Grader Operations
## 3 Path Generation Algorithm for Graders
### Heuristics of Grader Operators and Site Managers  
The operation of a grader is time consuming and labor intensive because of the simultaneous execution of measurement, calibration, driving, and grading during the grading process [27]. The quality and duration of work are highly dependent on the skill level of the operator. Therefore, this study conducted a heuristic investigation into the actual driving methods and patterns of graders by targeting skilled operators with 10 to over 30 years of experience as well as site managers (see Figure 3). As shown in Tables 1 and 2, the heuristic investigation was conducted based on grading, excluding the spread of materials. First, grading tasks typically involve handling a relatively small amount of material and are performed consistently. The progression of the work lines usually starts from the edge lines and moves inward towards the center, although in some cases, such as when adjusting the road's slope, the work may proceed from the center toward the edges. Because the amount of material to be graded is usually small, there is minimal buildup of soil on the blade, meaning that there is no fixed maximum advance distance, and operators can advance as needed. The sequence of work lines generally starts from the edge and moves towards the center of the road; however, in certain situations, such as setting the cross slope of the road, work may start from the center and proceed outward to the edge lines. The method for changing work lines is primarily determined based on the length of the work segment and the width of the non-working area, adjusted for the convenience of the operator. When a grader performs a task, it slightly overlaps the blade to ensure the quality and completeness of the work. In this study, the degree of this overlap is referred to as \"repeated rate\", and the blade width excluding the repeated area is termed \"effective width\". Typically, the repeated rate was approximately 50% [see Figure 4]. In Figure 4, x represents the extent of repeated rate. However, in cases where the work area is large or site conditions vary, the repeated rate can approach zero. The maximum advance distance of the grader varies depending on the type of work and amount of material to be handled. For grading tasks with minimal material, the grader may operate over long distances exceeding 300 m without restrictions. Conversely, in spreading tasks in which large quantities of material are processed, the working distance is often limited to approximately 5 m, depending on the volume of the material. Figure 3: Information of interviewees. In edge-line work on the road, the method can vary depending on the operator's skill level. In general, because the width of the grader's blade exceeds the width of the grader's body, skilled operators may extend the blade's edge slightly beyond the edge of the road or align it as closely as possible to achieve a perfect finish. In contrast, for less experienced operators, there is a risk of the equipment tipping over, so they typically keep the edge of the blade inside the road's edge line to ensure safety. The patterns of work are divided into two main types. In Pattern (a), the grader moves forward to complete a section, then turns around, and returns to proceed with the next work line by moving forward again (see Figure 5a). In Pattern (b), the grader moves forward to complete a section and then reverses back to the original starting line before moving forward again to begin the next work line (see Figure 5b).