BeaconPoseProvider

java.lang.Object
- lejos.robotics.localization.BeaconPoseProvider

All Implemented Interfaces:

PoseProvider, MoveListener
```
public class BeaconPoseProvider
extends java.lang.Object
implements PoseProvider, MoveListener
```
A PoseProvider that uses beacon triangulation to pinpoint the pose (x, y, heading) of a robot. The starting position of the robot must be such that it roughly points in the direction of beacon 2, with beacon 1 to the right of the robot, and beacon 3 to the left. This ensures that when it performs the first scan, the beacons are scanned in order 1, 2, 3. After the first scan, the robot can move about on its own and will be able to scan them in any order.

After it does a scan, you will either hear a beep or a buzz. A beep means the calculation worked. A buzz means something went wrong with the calculation. This could be the beacon ordering is wrong, or it didn't scan three beacons in, or the calculated beacon pose deviated significantly from the estimated odometry pose. In this case, the results are thrown out, the odometry pose is used, and it will try another scan after the next move. If you hear a lot of buzzes in a row, it probably means it will not recover.

The class uses an OdometryPoseProvider internally for three reasons:
1. To serve as a backup pose provider if the BeaconLocator detects less than 3 beacons, or greater than 3 (meaning a false reflection occurred).
2. It is time consuming to scan beacons after every move. Instead, this will scan about every 5 moves. In between these scans, it uses the OdometryPoseProvider to navigate.
3. It is essential to scan the beacons in order. This allows it to determine the identity of each beacon so they are properly fed to the equations. The OdometryPoseProvider keeps track of heading so it knows which beacons were scanned.

The downside of using an OdometryPoseProvider to assist with detecting pose is that the robot needs to be placed with an approximate heading prior to first scan. Also, if the robot is moved at any time (lifted and placed with a different heading), it probably will no longer be able to identify the beacons and become hopelessly lost. As long as the wheels are always on the ground, this should not happen.

Field Summary

Fields
Modifier and Type	Field and Description
`private BeaconLocator`	`bl`
`private BeaconTriangle`	`bt`
`private double`	`distance`
`private boolean`	`hasScanned`
`private int`	`moves`
`private OdometryPoseProvider`	`opp`
`private int`	`scanInterval`

Constructor Summary

Constructors
Constructor and Description
`BeaconPoseProvider(BeaconLocator bl, BeaconTriangle bt, MoveProvider mp)` Creates a PoseProvider using beacons.
`BeaconPoseProvider(BeaconLocator bl, BeaconTriangle bt, MoveProvider mp, int scanInterval)` Creates a PoseProvider using beacons.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`private static double`	`betweenAngles(double greater, double lesser)` Subtracts two angles in a clockwise direction.
`private static double`	`convertToRelative(double robotBearing, double cartesianHeading)` Converts the absolute Cartesian heading into the relative angle values the robot sees when scanning.
`static int`	`getLargestIndex(java.util.ArrayList<java.lang.Double> angles)`
`Pose`	`getPose()`
`void`	`moveStarted(Move move, MoveProvider mp)` Called when a Move Provider starts a move
`void`	`moveStopped(Move move, MoveProvider mp)` Called by the movement provider when a move stops
`void`	`setPose(Pose aPose)`
`private static boolean`	`sortBeacons(java.util.ArrayList<java.lang.Double> beacons, java.util.ArrayList<java.lang.Double> angles)` This sorts the beacons into the proper order so that beacons.get(0) returns beacon1, and so on.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - bt
```
private BeaconTriangle bt
```
  - bl
```
private BeaconLocator bl
```
  - opp
```
private OdometryPoseProvider opp
```
  - moves
```
private int moves
```
  - scanInterval
```
private int scanInterval
```
  - distance
```
private double distance
```
  - hasScanned
```
private boolean hasScanned
```
- Constructor Detail
  - BeaconPoseProvider
```
public BeaconPoseProvider(BeaconLocator bl,
                          BeaconTriangle bt,
                          MoveProvider mp)
```
    Creates a PoseProvider using beacons. The BeaconLocator must be capable of scanning the angles to 3 beacons. The BeaconTriangle contains the coordinates of the three beacons. The MoveProvider is simply a Pilot, such as DifferentialPilot, which is used to keep track of odometry.
    
    By default, this class takes a scan every 5 moves of the robot.
    
    Parameters:
    
    bl - a BeaconLocator
    
    bt - a BeaconTriangle containing the three beacon coordinates
    
    mp - a MoveProvider (Pilot) such as DifferentialPilot. Used for odometry.
  - BeaconPoseProvider
```
public BeaconPoseProvider(BeaconLocator bl,
                          BeaconTriangle bt,
                          MoveProvider mp,
                          int scanInterval)
```
    Creates a PoseProvider using beacons. The BeaconLocator must be capable of scanning the angles to 3 beacons. The BeaconTriangle contains the coordinates of the three beacons. The MoveProvider is simply a Pilot, such as DifferentialPilot, which is used to keep track of odometry.
    
    Parameters:
    
    bl - a BeaconLocator
    
    bt - a BeaconTriangle containing the three beacon coordinates
    
    mp - a MoveProvider (Pilot) such as DifferentialPilot. Used for odometry.
    
    scanInterval - The number of moves to make between each physical scan.
- Method Detail
  - convertToRelative
```
private static double convertToRelative(double robotBearing,
                                        double cartesianHeading)
```
    Converts the absolute Cartesian heading into the relative angle values the robot sees when scanning.
    
    Parameters:
    
    robotBearing - The heading the robot is currently at
    
    cartesianHeading - The absolute angle to a beacon from the robot, in Cartesian angle.
    
    Returns:
    
    relative angle
  - getPose
```
public Pose getPose()
```
    Specified by:
    
    getPose in interface PoseProvider
  - sortBeacons
```
private static boolean sortBeacons(java.util.ArrayList<java.lang.Double> beacons,
                                   java.util.ArrayList<java.lang.Double> angles)
```
    This sorts the beacons into the proper order so that beacons.get(0) returns beacon1, and so on. This method assumes beacons will always contain the beacon angles that were scanned in counter-clockwise.
    Strategy: Pick widest theoretical angle between beacons. There will always be one at least 120 degs. Then determine which beacon is clockwise of this angle.
    
    Parameters:
    
    beacons - an array of three angles.
    
    a1 -
    
    a2 -
    
    a3 -
  - getLargestIndex
```
public static int getLargestIndex(java.util.ArrayList<java.lang.Double> angles)
```
  - betweenAngles
```
private static double betweenAngles(double greater,
                                    double lesser)
```
    Subtracts two angles in a clockwise direction.
    
    Parameters:
    
    greater - The angle counter-clockwise of the other angle
    
    lesser - The other angle, clockwise from the other one
    
    Returns:
  - setPose
```
public void setPose(Pose aPose)
```
    Specified by:
    
    setPose in interface PoseProvider
  - moveStarted
```
public void moveStarted(Move move,
                        MoveProvider mp)
```
    Description copied from interface: MoveListener
    
    Called when a Move Provider starts a move
    
    Specified by:
    
    moveStarted in interface MoveListener
    
    Parameters:
    
    move - the movement
    
    mp - the movement provider
  - moveStopped
```
public void moveStopped(Move move,
                        MoveProvider mp)
```
    Description copied from interface: MoveListener
    
    Called by the movement provider when a move stops
    
    Specified by:
    
    moveStopped in interface MoveListener
    
    Parameters:
    
    move - the movement
    
    mp - movement provider

Class BeaconPoseProvider

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

bt

bl

opp

moves

scanInterval

distance

hasScanned

Constructor Detail

BeaconPoseProvider

BeaconPoseProvider

Method Detail

convertToRelative

getPose

sortBeacons

getLargestIndex

betweenAngles

setPose

moveStarted

moveStopped