| | | 1 | | using UnityEngine; |
| | | 2 | | |
| | | 3 | | // The iterative launch planner class is a launch planner that performs an iterative process to |
| | | 4 | | // determine the intercept point. The algorithm continuously performs the following 2-step iterative |
| | | 5 | | // process: |
| | | 6 | | // 1. Time-to-intercept estimation: The algorithm determines the time it takes the interceptor to |
| | | 7 | | // reach the target at the predicted intercept position, which is initialized to the target's |
| | | 8 | | // current position. |
| | | 9 | | // 2. Intercept position estimation: The algorithm predicts the target position at the estimated |
| | | 10 | | // time-to-intercept. |
| | | 11 | | public class IterativeLaunchPlanner : ILaunchPlanner { |
| | | 12 | | // Maximum number of iterations before declaring failure. |
| | | 13 | | private const int MaxNumIterations = 10; |
| | | 14 | | |
| | | 15 | | // Maximum intercept position threshold to declare convergence. |
| | | 16 | | private const float InterceptPositionThreshold = 1000; |
| | | 17 | | |
| | | 18 | | public IterativeLaunchPlanner(ILaunchAnglePlanner launchAnglePlanner, IPredictor predictor) |
| | 15 | 19 | | : base(launchAnglePlanner, predictor) {} |
| | | 20 | | |
| | | 21 | | // Plan the launch. |
| | 5 | 22 | | public override LaunchPlan Plan() { |
| | 5 | 23 | | PredictorState initialState = _predictor.Predict(time: 0); |
| | 5 | 24 | | Vector3 targetPosition = initialState.Position; |
| | 5 | 25 | | Vector2 initialTargetPositionDirection = |
| | | 26 | | ILaunchAnglePlanner.ConvertToDirection(initialState.Position); |
| | | 27 | | |
| | 5 | 28 | | LaunchAngleOutput launchAngleOutput = new LaunchAngleOutput(); |
| | 5 | 29 | | Vector2 interceptDirection = Vector2.zero; |
| | 5 | 30 | | Vector2 predictedDirection = Vector2.zero; |
| | 30 | 31 | | for (int i = 0; i < MaxNumIterations; ++i) { |
| | | 32 | | // Estimate the time-to-intercept. |
| | 10 | 33 | | launchAngleOutput = _launchAnglePlanner.Plan(targetPosition); |
| | 10 | 34 | | float timeToIntercept = launchAngleOutput.TimeToPosition; |
| | 10 | 35 | | LaunchAngleInput launchAngleInput = _launchAnglePlanner.GetInterceptPosition(targetPosition); |
| | | 36 | | |
| | | 37 | | // Estimate the intercept position. |
| | 10 | 38 | | PredictorState predictedState = _predictor.Predict(timeToIntercept); |
| | 10 | 39 | | targetPosition = predictedState.Position; |
| | | 40 | | |
| | | 41 | | // Check whether the intercept direction has changed, in which case the algorithm has |
| | | 42 | | // converged. |
| | 10 | 43 | | Vector2 newInterceptDirection = |
| | | 44 | | new Vector2(launchAngleInput.Distance, launchAngleInput.Altitude); |
| | 14 | 45 | | if (interceptDirection == newInterceptDirection) { |
| | 4 | 46 | | break; |
| | | 47 | | } |
| | 6 | 48 | | interceptDirection = newInterceptDirection; |
| | 6 | 49 | | predictedDirection = ILaunchAnglePlanner.ConvertToDirection(targetPosition); |
| | | 50 | | |
| | | 51 | | // Check that the target is moving towards the intercept position. |
| | 6 | 52 | | if (Vector2.Dot(interceptDirection - initialTargetPositionDirection, |
| | 1 | 53 | | predictedDirection - initialTargetPositionDirection) < 0) { |
| | | 54 | | // The interceptor should wait to be launched. |
| | 1 | 55 | | return LaunchPlan.NoLaunch; |
| | | 56 | | } |
| | 5 | 57 | | } |
| | | 58 | | |
| | | 59 | | // Check whether the intercept position and the predicted position are within some threshold |
| | | 60 | | // distance of each other. |
| | 7 | 61 | | if (Vector2.Distance(interceptDirection, predictedDirection) < InterceptPositionThreshold) { |
| | 3 | 62 | | return new LaunchPlan(launchAngleOutput.LaunchAngle, targetPosition); |
| | | 63 | | } |
| | 1 | 64 | | return LaunchPlan.NoLaunch; |
| | 5 | 65 | | } |
| | | 66 | | } |