source: branches/Robocode.TrunkInt/HeuristicLab.Problems.Robocode/3.3/robocode/robots/samplesentry/BorderGuard.java @ 13083

/**
 * Copyright (c) 2001-2014 Mathew A. Nelson and Robocode contributors
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://robocode.sourceforge.net/license/epl-v10.html
 */
package samplesentry;


import robocode.*;
import robocode.util.Utils;

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.geom.Point2D;
import java.util.*;


/**
 * BorderGuard - is a sample robot that demonstrates how the BorderSentry interface can be used for
 * creating a robot that guards the border area of the battle field, and which is efficient against
 * robots trying to hide at corners and robots sneaking around near the borders.
 * <p>
 * This robot is somewhat advanced due to:<br>
 * 1) it uses linear targeting for predicting how to hit robots that moves in straight lines.<br>
 * 2) it will only fire at a robot, if it figures out that its bullets will do damage to that
 * particular robot, e.g. when the robots predicted future position will be within the sentry border
 * attack range.<br>
 * 3) it has an efficient scanner that keeps the scan angle as little as possible to get as new
 * scanned data for enemy robots as possible.<br>
 * 4) it picks a target robot to fire at, which is the nearest robot our robot will be able to
 * damage (by predicting its future position using linear targeting).<br>
 * 5) it only moves along the borders of the battle field and constantly changes its direction, so
 * it is not an easy target, and it will try to get as close to its target robot as possible.<br>
 * <p>
 * Lots of improvements can be made to this robot by copying it - making it even stronger. The
 * intention with of this sample robot is to serve as a more advanced example of how a AdvancedRobot
 * can be made, and how it can be structured as most sample robots are far simpler.
 * <p>
 * 
 * Credits goes to the hard working Robocoders at the RoboWiki. :-)
 * <p>
 * 
 * This robot makes use of the Oldest Scanned melee scanner from the RoboWiki:<br>
 * http://robowiki.net/wiki/Melee_Radar
 * <p>
 * 
 * In addition, it makes use of the Exact Non-iterative Solution for Linear Targeting from the
 * RoboWiki:<br>
 * http://robowiki.net/wiki/Linear_Targeting
 * 
 * @author Flemming N. Larsen
 * 
 * @version 1.0
 * 
 * @since 1.9.0.0
 */
public class BorderGuard extends AdvancedRobot implements BorderSentry {

  // Constants
  final double FIREPOWER = 3; // Max. power => violent as this robot can afford it!
  final double HALF_ROBOT_SIZE = 18; // Robot size is 36x36 units, so the half size is 18 units

  // Map containing data for all scanned robots.
  // The key to the map is a robot name and the value is an object containing robot data.
  final Map<String, RobotData> enemyMap;

  // Scanning direction, where the radar turns to the right with positive values, and turns
  // to the left with negative values.
  double scanDir = 1;

  // Oldest scanned robot. Can be null.
  RobotData oldestScanned;

  // Target robot for the gun. Can be null meaning that there is currently no target robot.
  RobotData target;

  // Last time when the robot shifted its direction
  long lastDirectionShift;

  // Current direction, where 1 means ahead (forward) and -1 means back
  int direction = 1;

  /**
   * Constructs this robot.
   */
  public BorderGuard() {
    // We initialize a specialized HashMap that uses a linked list for the access order.
    // This means that the last accessed robot entry is listed first, when we iterate over its
    // values. This robot always sweep the radar towards the oldest scanned robot.
    enemyMap = new LinkedHashMap<String, RobotData>(5, 2, true);
  }

  /**
   * Main method that is called by the game when the robot engage in the next round of a battle.
   */
  @Override
  public void run() {
    // Do initialization stuff here before the loop
    initialize();

    // Loop forever. If the robot does not take action, the game will disable our robot!
    while (true) {
      // Handle a single turn...

      // Handle the radar that scans enemy robots
      handleRadar();
      // Handle the gun by turning it and fire at our target
      handleGun();
      // Move the robot around on the battlefield
      moveRobot();

      // Scan for other robots. Note that this method will execute all pending commands for
      // the next turn. Hence, scan() ends the turn for our robot.
      scan();
    }
  }

  /**
   * This method is called by the game when your robot sees another robot, i.e. when the robot's
   * radar scan "hits" another robot.
   * 
   * @param scannedRobotEvent
   *            is a ScannedRobotEvent event.
   */
  @Override
  public void onScannedRobot(ScannedRobotEvent scannedRobotEvent) {
    // Check that the scanned robot is not a sentry robot
    if (!scannedRobotEvent.isSentryRobot()) {
      // The scanned robot is not a sentry robot...

      // Update the enemy map
      updateEnemyMap(scannedRobotEvent);

      // Update the scan direction
      updateScanDirection(scannedRobotEvent);

      // Update enemy target positions
      updateEnemyTargetPositions();
    }
  }

  /**
   * This method is called by the game when another robot dies.
   * 
   * @param robotDeathEvent
   *            is the RobotDeathEvent that occurs, when another robot dies, which contains data
   *            for the robot that died.
   */
  @Override
  public void onRobotDeath(RobotDeathEvent robotDeathEvent) {
    // Gets the name of the robot that died
    final String deadRobotName = robotDeathEvent.getName();

    // Remove the robot data for the robot that died from the enemy map
    enemyMap.remove(deadRobotName);

    // Remove the data entry for the oldest scanned robot, if we have such an entry
    if (oldestScanned != null && oldestScanned.name.equals(deadRobotName)) {
      oldestScanned = null;
    }
    if (target != null && target.name.equals(deadRobotName)) {
      target = null;
    }
  }

  /**
   * This method is called by the every time the robot is painted. In order to see the painting,
   * make sure to enable the Paint button on the robot console for this robot.
   * 
   * @param g
   *            is the {@link Graphics2D} object, which is the graphics context used for painting
   *            various shapes like rectangles, circles, lines etc. on top of the battlefield for
   *            debugging graphics.
   */
  @Override
  public void onPaint(Graphics2D g) {
    // Set the line width to 2 pixels
    g.setStroke(new BasicStroke(2f));

    // Prepare colors for painting the scanned coordinate and target coordinate
    Color color1 = new Color(0x00, 0xFF, 0x00, 0x40); // Green with 25% alpha blending
    Color color2 = new Color(0xFF, 0xFF, 0x00, 0x40); // Yellow with 25% alhpa blending

    // Paint a two circles for each robot in the enemy map. One circle where the robot was
    // scanned the last time, and another circle where our robot must point the gun in order to
    // hit it (target coordinate). In addition, a line is drawn between these circles.
    for (RobotData robot : enemyMap.values()) {
      // Paint the two circles and a line
      fillCircle(g, robot.scannedX, robot.scannedY, color1); // scanned coordinate
      fillCircle(g, robot.targetX, robot.targetY, color2); // target coordinate
      g.setColor(color1);
      g.drawLine((int) robot.scannedX, (int) robot.scannedY, (int) robot.targetX, (int) robot.targetY);
    }

    // Paint a two circles for the target robot. One circle where the robot was
    // scanned the last time, and another circle where our robot must point the gun in order to
    // hit it (target coordinate). In addition, a line is drawn between these circles.
    if (target != null) {
      // Prepare colors for painting the scanned coordinate and target coordinate
      color1 = new Color(0xFF, 0x7F, 0x00, 0x40); // Orange with 25% alpha blending
      color2 = new Color(0xFF, 0x00, 0x00, 0x80); // Red with 50% alpha blending

      // Paint the two circles and a line
      fillCircle(g, target.scannedX, target.scannedY, color1); // scanned coordinate
      fillCircle(g, target.targetX, target.targetY, color2); // target coordinate
      g.setColor(color1);
      g.drawLine((int) target.scannedX, (int) target.scannedY, (int) target.targetX, (int) target.targetY);
    }
  }

  /**
   * Initializes this robot before a new round in a battle.
   */
  private void initialize() {
    // Let the robot body, gun, and radar turn independently of each other
    setAdjustRadarForGunTurn(true);
    setAdjustGunForRobotTurn(true);

    // Set robot colors
    setBodyColor(new Color(0x5C, 0x33, 0x17)); // Chocolate Brown
    setGunColor(new Color(0x45, 0x8B, 0x74)); // Aqua Marine
    setRadarColor(new Color(0xD2, 0x69, 0x1E)); // Orange Chocolate
    setBulletColor(new Color(0xFF, 0xD3, 0x9B)); // Burly wood
    setScanColor(new Color(0xCA, 0xFF, 0x70)); // Olive Green
  }

  /**
   * This method handles the radar that scans for enemy robots.
   */
  private void handleRadar() {
    // Set the radar to turn infinitely to the right if the scan direction is positive;
    // otherwise the radar is moved to the left, if the scan direction is negative.
    // Notice that onScannedRobot(ScannedRobotEvent) is responsible for determining the scan
    // direction.
    setTurnRadarRightRadians(scanDir * Double.POSITIVE_INFINITY);
  }

  /**
   * Method that handles the gun be turning it and fire at a target.
   */
  private void handleGun() {
    // Update our target robot to fire at
    updateTarget();
    // Update the gun direction
    updateGunDirection();
    // Fires the gun, when it is ready
    fireGunWhenReady();
  }

  /**
   * Method that moves our robot around the battlefield.
   */
  private void moveRobot() {

    // The movement strategy is to move as close to our target robot as possible.
    // Our robot should move along the borders all the time, vertically or horizontally.
    // When we get close to our target, or have no where to go, our robot should shift its
    // direction from side to side so it does not stand still at any time.
    // If the robot stands still, it will be an easy target for enemy robots.

    int newDirection = direction;

    // Get closer to our target if we have a target robot
    if (target != null) {
      // Calculate the range from the walls/borders, our robot should keep within
      int borderRange = getSentryBorderSize() - 20;

      // The horizontal and vertical flags are used for determining, if our robot should
      // move horizontal or vertical.
      boolean horizontal = false;
      boolean vertical = false;

      // Initialize the new heading of the robot to the current heading of the robot
      double newHeading = getHeadingRadians();

      // Check if our robot is at the upper or lower border and hence should move horizontally
      if (getY() < borderRange || getY() > getBattleFieldHeight() - borderRange) {
        horizontal = true;
      }
      // Check if our robot is at the left or right border and hence should move vertically
      if (getX() < borderRange || getX() > getBattleFieldWidth() - borderRange) {
        vertical = true;
      }

      // If we are in one of the corners of the battlefield, we could move both horizontally
      // or vertically.
      // In this situation, we need to choose one of the two directions.
      if (horizontal && vertical) {
        // If the horizontal distance to our target is lesser than the vertical distance,
        // then we choose to move vertically, and hence we clear the horizontal flag.
        if (Math.abs(target.targetX - getX()) <= Math.abs(target.targetY - getY())) {
          horizontal = false; // Do not move horizontally => move vertically
        }
      }
      // Adjust the heading of our robot with 90 degrees, if it must move horizontally.
      // Otherwise the calculated heading is towards moving vertically.
      if (horizontal) {
        newHeading -= Math.PI / 2;
      }
      // Set the robot to turn left the amount of radians we have just calculated
      setTurnLeftRadians(Utils.normalRelativeAngle(newHeading));

      // Check if our robot has finished turning, i.e. has less than 1 degrees left to turn
      if (Math.abs(getTurnRemaining()) < 1 || Math.abs(getVelocity()) < 0.01) {
        // If we should move horizontally, the set the robot to move ahead with the
        // horizontal distance to the target robot. Otherwise, use the vertical distance.
        double delta; // delta is the delta distance to move
        if (horizontal) {
          delta = target.targetX - getX();
        } else {
          delta = target.targetY - getY();
        }
        setAhead(delta);

        // Set the new direction of our robot to 1 (meaning move forward) if the delta
        // distance is positive; otherwise it is set to -1 (meaning move backward).
        newDirection = delta > 0 ? 1 : -1;

        // Check if more than 10 turns have past since we changed the direction the last
        // time
        if (getTime() - lastDirectionShift > 10) {
          // If so, set the new direction to be the reverse direction if the velocity < 1
          if (Math.abs(getVelocity()) < 1) {
            newDirection = direction * -1;
          }
          // Check if the direction really changed
          if (newDirection != direction) {
            // If the new direction != current direction, then set the current direction
            // to be the new direction and save the current time so we know when we
            // changed the direction the last time.
            direction = newDirection;
            lastDirectionShift = getTime();
          }
        }
      }
    }
    // Set ahead 100 units forward or backward depending on the direction
    setAhead(100 * direction);
  }

  /**
   * Method the updates the enemy map based on new scan data for a scanned robot.
   * 
   * @param scannedRobotEvent
   *            is a ScannedRobotEvent event containing data about a scanned robot.
   */
  private void updateEnemyMap(ScannedRobotEvent scannedRobotEvent) {
    // Gets the name of the scanned robot
    final String scannedRobotName = scannedRobotEvent.getName();

    // Get robot data for the scanned robot, if we have an entry in the enemy map
    RobotData scannedRobot = enemyMap.get(scannedRobotName);

    // Check if data entry exists for the scanned robot
    if (scannedRobot == null) {
      // No data entry exists => Create a new data entry for the scanned robot
      scannedRobot = new RobotData(scannedRobotEvent);
      // Put the new data entry into the enemy map
      enemyMap.put(scannedRobotName, scannedRobot);
    } else {
      // Data entry exists => Update the current entry with new scanned data
      scannedRobot.update(scannedRobotEvent);
    }
  }

  /**
   * Method that updates the direction of the radar based on new scan data for a scanned robot.
   * 
   * @param scannedRobotEvent
   *            is a ScannedRobotEvent event containing data about a scanned robot.
   */
  private void updateScanDirection(ScannedRobotEvent scannedRobotEvent) {
    // Gets the name of the scanned robot
    final String scannedRobotName = scannedRobotEvent.getName();

    // Change the scanning direction if and only if we have no record for the oldest scanned
    // robot or the scanned robot IS the oldest scanned robot (based on the name) AND the enemy
    // map contains scanned data entries for ALL robots (the size of the enemy map is equal to
    // the number of opponent robots found by calling the getOthers() method).
    if ((oldestScanned == null || scannedRobotName.equals(oldestScanned.name)) && enemyMap.size() == getOthers()) {

      // Get the oldest scanned robot data from our LinkedHashMap, where the first value
      // contains the oldest accessed entry, which is the robot we need to get.
      RobotData oldestScannedRobot = enemyMap.values().iterator().next();

      // Get the recent scanned position (x,y) of the oldest scanned robot
      double x = oldestScannedRobot.scannedX;
      double y = oldestScannedRobot.scannedY;

      // Get the heading of our robot
      double ourHeading = getRadarHeadingRadians();

      // Calculate the bearing to the oldest scanned robot.
      // The bearing is the delta angle between the heading of our robot and the other robot,
      // which can be a positive or negative angle.
      double bearing = bearingTo(ourHeading, x, y);

      // Update the scan direction based on the bearing.
      // If the bearing is positive, the radar will be moved to the right.
      // If the bearing is negative, the radar will be moved to the left.
      scanDir = bearing;
    }
  }

  /**
   * Updates the target positions for all enemies. The target position is the position our robot
   * must fire at in order to hit the target robot. This robot uses Linear Targeting (Exact
   * Non-iterative Solution) as described on the RoboWiki here:
   * http://robowiki.net/wiki/Linear_Targeting
   */
  private void updateEnemyTargetPositions() {
    // Go thru all robots in the enemy map
    for (RobotData enemy : enemyMap.values()) {

      // Variables prefixed with e- refer to enemy and b- refer to bullet
      double bV = Rules.getBulletSpeed(FIREPOWER);
      double eX = enemy.scannedX;
      double eY = enemy.scannedY;
      double eV = enemy.scannedVelocity;
      double eH = enemy.scannedHeading;

      // These constants make calculating the quadratic coefficients below easier
      double A = (eX - getX()) / bV;
      double B = (eY - getY()) / bV;
      double C = eV / bV * Math.sin(eH);
      double D = eV / bV * Math.cos(eH);

      // Quadratic coefficients: a*(1/t)^2 + b*(1/t) + c = 0
      double a = A * A + B * B;
      double b = 2 * (A * C + B * D);
      double c = (C * C + D * D - 1);

      // If the discriminant of the quadratic formula is >= 0, we have a solution meaning that
      // at some time, t, the bullet will hit the enemy robot if we fire at it now.
      double discrim = b * b - 4 * a * c;
      if (discrim >= 0) {
        // Reciprocal of quadratic formula. Calculate the two possible solution for the
        // time, t
        double t1 = 2 * a / (-b - Math.sqrt(discrim));
        double t2 = 2 * a / (-b + Math.sqrt(discrim));

        // Choose the minimum positive time or select the one closest to 0, if the time is
        // negative
        double t = Math.min(t1, t2) >= 0 ? Math.min(t1, t2) : Math.max(t1, t2);

        // Calculate the target position (x,y) for the enemy. That is the point that our gun
        // should point at in order to hit the enemy at the time, t.
        double targetX = eX + eV * t * Math.sin(eH);
        double targetY = eY + eV * t * Math.cos(eH);

        // Assume enemy stops at walls. Hence, we limit that target position at the walls.
        double minX = HALF_ROBOT_SIZE;
        double minY = HALF_ROBOT_SIZE;
        double maxX = getBattleFieldWidth() - HALF_ROBOT_SIZE;
        double maxY = getBattleFieldHeight() - HALF_ROBOT_SIZE;

        enemy.targetX = limit(targetX, minX, maxX);
        enemy.targetY = limit(targetY, minY, maxY);
      }
    }
  }

  /**
   * Updates which enemy robot from the enemy map that should be our current target.
   */
  private void updateTarget() {
    // Set target to null, meaning that we have no target robot yet
    target = null;

    // Create a list over possible target robots that is a copy of robot data from the enemy map
    List<RobotData> targets = new ArrayList<RobotData>(enemyMap.values());

    // Run thru all the possible target robots and remove those that are outside the attack
    // range for this border sentry robot as our robot cannot do harm to robots outside its
    // range.
    Iterator<RobotData> it = targets.iterator();
    while (it.hasNext()) {
      RobotData robot = it.next();
      if (isOutsideAttackRange(robot.targetX, robot.targetY)) {
        it.remove();
      }
    }

    // Set the target robot to be the one among all possible target robots that is closest to
    // our robot.
    double minDist = Double.POSITIVE_INFINITY;
    for (RobotData robot : targets) {
      double dist = distanceTo(robot.targetX, robot.targetY);
      if (dist < minDist) {
        minDist = dist;
        target = robot;
      }
    }

    // If we still haven't got a target robot, then take the first one from our list of target
    // robots if the list is not empty.
    if (target == null && targets.size() > 0) {
      target = targets.get(0);
    }
  }

  /**
   * Method that updates the gun direction to point at the current target.
   */
  private void updateGunDirection() {
    // Only update the gun direction, if we have a current target
    if (target != null) {
      // Calculate the bearing between the gun and the target, which can be positive or
      // negative
      double targetBearing = bearingTo(getGunHeadingRadians(), target.targetX, target.targetY);
      // Set the gun to turn right the amount of radians defined by the bearing to the target
      setTurnGunRightRadians(targetBearing); // positive => turn right, negative => turn left
    }
  }

  /**
   * Method that fires a bullet when the gun is ready to fire.
   */
  private void fireGunWhenReady() {
    // We only fire the fun, when we have a target robot
    if (target != null) {
      // Only fire when the angle of the gun is pointing at our (virtual) target robot

      // Calculate the distance between between our robot and the target robot
      double dist = distanceTo(target.targetX, target.targetY);
      // Angle that "covers" the the target robot from its center to its edge
      double angle = Math.atan(HALF_ROBOT_SIZE / dist);

      // Check if the remaining angle (turn) to move the gun is less than our calculated cover
      // angle
      if (Math.abs(getGunTurnRemaining()) < angle) {
        // If so, our gun should be pointing at our target so we can hit it => fire!!
        setFire(FIREPOWER);
      }
    }
  }

  /**
   * Method that checks if a coordinate (x,y) is outside the Border Sentry's attack range.
   * 
   * @param x
   *            is the x coordinate.
   * @param y
   *            is the y coordinate.
   * @return true if the coordinate is outside the attack range; false otherwise.
   */
  private boolean isOutsideAttackRange(double x, double y) {
    double minBorderX = getSentryBorderSize();
    double minBorderY = getSentryBorderSize();
    double maxBorderX = getBattleFieldWidth() - getSentryBorderSize();
    double maxBorderY = getBattleFieldHeight() - getSentryBorderSize();

    return (x > minBorderX) && (y > minBorderY) && (x < maxBorderX) && (y < maxBorderY);
  }

  /**
   * Method that returns a value that is guaranteed to be within a value range defined by a
   * minimum and maximum value based on an input value.<br>
   * If the input value is lesser than the minimum value, the returned value will be set to the
   * minimum value.<br>
   * If the input value is greater than the maximum value, the returned value will be set to the
   * maximum value.<br>
   * Otherwise the returned value will be equal to the input value.
   * 
   * @param value
   *            is the input value to limit.
   * @param min
   *            is the allowed minimum value.
   * @param max
   *            is the allowed maximum value.
   * @return the limited input value that is guaranteed to be within the specified minimum and
   *         maximum range.
   */
  private double limit(double value, double min, double max) {
    return Math.min(max, Math.max(min, value));
  }

  /**
   * Methods that returns the distance to a coordinate (x,y) from our robot.
   * 
   * @param x
   *            is the x coordinate.
   * @param y
   *            is the y coordinate.
   * @return the distance to the coordinate (x,y).
   */
  private double distanceTo(double x, double y) {
    return Math.hypot(x - getX(), y - getY());
  }

  /**
   * Method that returns the angle to a coordinate (x,y) from our robot.
   * 
   * @param x
   *            is the x coordinate.
   * @param y
   *            is the y coordinate.
   * @return the angle to the coordinate (x,y).
   */
  private double angleTo(double x, double y) {
    return Math.atan2(x - getX(), y - getY());
  }

  /**
   * Method that returns the bearing to a coordinate (x,y) from the position and heading of our
   * robot. The bearing is the delta angle between the heading of our robot and the angle of the
   * specified coordinate.
   * 
   * @param x
   *            is the x coordinate.
   * @param y
   *            is the y coordinate.
   * @return the angle to the coordinate (x,y).
   */
  private double bearingTo(double heading, double x, double y) {
    return Utils.normalRelativeAngle(angleTo(x, y) - heading);
  }

  /**
   * Method that paints a filled circle at the specified coordinate (x,y) and given color. The
   * circle will have a radius of 20 pixels (meaning that the diameter will be 40 pixels).
   * 
   * @param gfx
   *            is the graphics context to draw within.
   * @param x
   *            is the x coordinate for the center of the circle.
   * @param y
   *            is the y coordinate for the center of the circle.
   * @param color
   *            is the color of the filled circle.
   */
  private void fillCircle(Graphics2D gfx, double x, double y, Color color) {
    // Set the pen color
    gfx.setColor(color);
    // Paint a filled circle (oval) that has a radius of 20 pixels with a center at the input
    // coordinates.
    gfx.fillOval((int) x - 20, (int) y - 20, 40, 40);
  }

  /**
   * This class is used for storing data about a robot that has been scanned.<br>
   * The data is mainly a snapshot of specific scanned data like the scanned position (x,y),
   * velocity and heading, put also the calculated predicted target position of the robot when our
   * robot needs to fire at the scanned robot.<br>
   * Note that this class calculates the position (x,y) of the scanned robot as our robot moves,
   * and hence data like the angle and distance to the scanned robot will change over time. by
   * using the position, it is easy to calculate a new angle and distance to the robot.
   */
  class RobotData {
    final String name; // name of the scanned robot
    double scannedX; // x coordinate of the scanned robot based on the last update
    double scannedY; // y coordinate of the scanned robot based on the last update
    double scannedVelocity; // velocity of the scanned robot from the last update
    double scannedHeading; // heading of the scanned robot from the last update
    double targetX; // predicated x coordinate to aim our gun at, when firing at the robot
    double targetY; // predicated y coordinate to aim our gun at, when firing at the robot

    /**
     * Creates a new robot data entry based on new scan data for a scanned robot.
     * 
     * @param event
     *            is a ScannedRobotEvent event containing data about a scanned robot.
     */
    RobotData(ScannedRobotEvent event) {
      // Store the name of the scanned robot
      name = event.getName();
      // Updates all scanned facts like position, velocity, and heading
      update(event);
      // Initialize the coordinates (x,y) to fire at to the updated scanned position
      targetX = scannedX;
      targetY = scannedY;
    }

    /**
     * Updates the scanned data based on new scan data for a scanned robot.
     * 
     * @param event
     *            is a ScannedRobotEvent event containing data about a scanned robot.
     */
    void update(ScannedRobotEvent event) {
      // Get the position of the scanned robot based on the ScannedRobotEvent
      Point2D.Double pos = getPosition(event);
      // Store the scanned position (x,y)
      scannedX = pos.x;
      scannedY = pos.y;
      // Store the scanned velocity and heading
      scannedVelocity = event.getVelocity();
      scannedHeading = event.getHeadingRadians();
    }

    /**
     * Returns the position of the scanned robot based on new scan data for a scanned robot.
     * 
     * @param event
     *            is a ScannedRobotEvent event containing data about a scanned robot.
     * @return the position (x,y) of the scanned robot.
     */
    Point2D.Double getPosition(ScannedRobotEvent event) {
      // Gets the distance to the scanned robot
      double distance = event.getDistance();
      // Calculate the angle to the scanned robot (our robot heading + bearing to scanned
      // robot)
      double angle = getHeadingRadians() + event.getBearingRadians();

      // Calculate the coordinates (x,y) of the scanned robot
      double x = getX() + Math.sin(angle) * distance;
      double y = getY() + Math.cos(angle) * distance;

      // Return the position as a point (x,y)
      return new Point2D.Double(x, y);
    }
  }
}