# Automating the Short-Loading Cycle: Survey and Integration Framework
## 3 Automation of Wheel Loaders
### Survey
#### 3.2.2 Navigation  
When it comes to navigation between the pile and the tipping body, very little has been achieved in terms of examining how data-driven approaches can be used for navigation; however, quite a lot of rule-based solutions have been proposed. Very few of these solutions have been demonstrated on a real wheel loader in a realistic environment. Clothoid-based path generation and tracking have been used not only to navigate towards the pile but also to navigate between the pile and the dump truck [37]. The generated path consists of two symmetrical clothoids connected at the reversal point, where the first clothoid is tracked during reversing and the second is tracked during forward motion. Due to wheel loaders being a type of actuated vehicle, the tracking point on the wheel loader has to change throughout navigation. While reversing, the tracking point is the centre of the back axle and while moving forward, the tracking point is the centre of the front axle. This clothoid solution is extended to include a larger amount of types of path generation situations, including the generating a path between pile and dump truck [38]. A canonical path skeleton is defined between a set of points costing three line segments and two clothoids, which is then optimized using two different methods. The first method is a genetic algorithm and the second is a form of quadratic programming. The methods search through the variables and parameters for a set amount of time and once finished, the semi-optimal path is retrieved, where it is optimally defined as the length of the path. A similar optimization algorithm is based on a genetic algorithm, where the path is assumed to include a straight line, a clothoid curve, and a circle line [39]. The optimization criterion is the path length, and the genetic algorithm runs for 1000 iterations before returning the semi-optimal path. Both of these solutions are validated on a miniature wheel loader, showing that both solutions have potential. An extended version of the Reeds-Shepp [40] algorithm has been used to generate the trajectory between the pile and the tipping body [41]. The generated optimal path, where the optimality criteria are based on distance and cusp minimization, consists of circular arcs and straight segments. To perform the path following the generated trajectory, a PID is used to control the lateral position with constant velocity. Ref. [42] used an algorithm based on RRT* and CC steer to plan the trajectory between the pile and the tipping body. The generated trajectory was tracked using an AMPC tracking system that considers the curvature disturbances in the trajectory resulting from the wheel loader's acceleration and deceleration. Neither of these solutions considered the lift speed of the boom in the proposed solutions. Most of the previous work has examined cases where a trajectory needs to be generated between a single loading and unloading point. However, the short-loading cycle consists of multiple scooping and unloading points as it takes more than a single bucket to fill the tipping body of a dump truck. Ref. [43] proposed an algorithm that calculates multiple scooping points for a single unload point and tested it in a simulation. This was achieved by creating a score space containing the length of each path in the global space and generating, from this score space, all paths using CC paths. The solution was validated on a miniature wheel loader. Furthermore, ref. [44] proposed another solution to generate paths between multiple arbitrary loading points and a single unloading point. This was achieved by decomposing the problem into three distinct tasks. The first task revolves around finding a set of candidate scooping points from a cost map. The second task ranks these points using reinforcement learning to obtain the actual set of scooping points. From this, the last task uses CC paths to generate the continuous path to excavate the gravel pile and transfer the material to the tipping body of the dump truck.