Difference between revisions of "Radar"

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The radar is one of the most vital components of your robot. Without it, [[targeting]] is effectively impossible and [[movement]] is purely random. Just as with movement and targeting, there are many simple and complex algorithms for radar control. In most robots the radar takes up the smallest portion of code.
+
[[Image:Radar.png|thumb|right|300px|Radar in [[Robocode]]]]
  
−
In robots that do a lot of processing, it is best to place the radar code near the beginning of the processing loop for each tick, as this will allow the radar to avoid slipping if the robot [[Skipped Turns|skips a turn]] due to too much processing.
+
'''Radar''' is one of the most vital components of your robot. Without it, [[targeting]] is effectively impossible and [[movement]] is purely random. Just as with movement and targeting, there are many simple and complex algorithms for radar control. In most robots the radar takes up the smallest portion of code.
  
 +
== Technical information ==
 +
A radar in Robocode can turn a maximum of 45° or &pi;/4 rad in a single tick. The radar scans robots up to 1200 units away. The angle that the radar rotates between two ticks creates what is called a radar arc, and every robot detected within the arc is sent to the <code>onScannedRobot()</code> method in order of distance from the scanning bot. The closest bot is detected first, while the furthest bot is detected last. By default, the <code>onScannedRobot()</code> method has the lowest event priority of all the event handlers in Robocode, so it is the last one to be triggered each tick.
  
−
== Technical Information ==
+
== Prerequisites ==
−
A radar in Robocode can turn a maximum of 45° or &pi;/4<sup>rad</sup> in a single tick. The radar scans robots up to 1200 units away. The angle that the radar rotates between two ticks creates what is called a radar arc, and every robot detected within the arc is sent to the <code>onScannedRobot()</code> method in order of distance from the scanning bot. The closest bot is detected first, while the furthest bot is detected last. By default, the <code>onScannedRobot()</code> method has the lowest [[event priority]] of all the event handlers in Robocode, so it is the last one to be triggered each tick.
+
Before you start implementing a radar, you should have:
 +
# Followed the [[Robocode/My First Robot|My First Robot Tutorial]], and created a robot.
 +
# Read the [[Robocode/FAQ|FAQ]], understood non-blocking calls, and switched your robot to an <code>AdvancedRobot</code>.
 +
# Gotten a good understanding of Java and at least a basic familiarity of the [http://robocode.sourceforge.net/docs/robocode/ Robocode API].
  
−
== 1-vs-1 Radars ==
+
If you haven't done all of these, do them first. Otherwise, this article will only make you more confused.
−
1-vs-1 radars are the smallest of the bunch and many can get a scan in every turn, producing a perfect lock.
 
  
−
=== Spinning radar ===
+
== Display scan arcs ==
−
A simple spin of the radar, this is very ineffective in one on one, but still used in [[NanoBot]]s.
+
By default, Robocode hides radar arcs, to prevent visual overload. This is a good idea in large [[melee]] battles, but not when debugging your radar.
  
−
Here is an example of this type of radar:
+
Scan arcs can be enabled in Robocode's Preferences:
−
<pre>
 
−
public void run() {
 
−
    // ...
 
  
−
    do {
+
[[File:EnableScanArcs.png]]
−
        turnRadarRightRadians(Double.POSITIVE_INFINITY);
 
−
    } while (true);
 
−
}
 
−
</pre>
 
  
−
=== The infinity lock ===
+
== Configure the radar ==
−
The infinity lock is the simplest radar lock and it is used frequently in [[NanoBots]]. It has the disadvantage of "slipping" and losing its lock frequently. But is a much better alternative to the Spinning radar in one on one combat.
+
Your first action in <code>run()</code> should '''always''' be:
  
−
Here is an example of this type of radar:
+
<syntaxhighlight>
−
<pre>
+
setAdjustGunForRobotTurn(true);
−
public void run() {
+
setAdjustRadarForGunTurn(true);
−
    // ...
+
</syntaxhighlight>
−
    turnRadarRightRadians(Double.POSITIVE_INFINITY);
 
−
}
 
  
−
public void onScannedRobot(ScannedRobotEvent e) {
+
This allows your robot's base, gun, and radar to rotate independently. It is practically essential for radar locks and any form of accurate targeting.
−
    // ...
 
−
    setTurnRadarLeftRadians(getRadarTurnRemainingRadians());
 
−
}
 
−
</pre>
 
  
−
=== Perfect radar locks ===
+
== At round start ==
−
There are several "perfect" radar locks that will not slip once they have a lock.
+
One of the first actions your robot performs should be to turn the radar as much as possible. A simple implementation would be:
  
−
==== Narrow lock ====
+
<syntaxhighlight>
−
Point the radar at the enemy's last known location. This results in a thin beam which follows the enemy around the battlefield. It works because most of the time, the enemy isn't able to move entirely outside our radar beam in the space of a single turn. This might not be true in some extreme cases, and radar lock can occasionally be lost but this can be fixed by factor describe below. Most top bot (that I figure out) use this kind of radar.
+
setTurnRadarRight(Double.POSITIVE_INFINITY);
 +
</syntaxhighlight>
  
−
Here is an example of this kind of radar:
+
This causes the radar to begin turning clockwise, forever. However, it may not be wise to always turn the radar clockwise. Sometimes, turning it counterclockwise might provide more information, faster. The optimal scan direction is the one with the shortest rotational difference to the angle between the robot and the battlefield center.  
−
<pre>
 
−
import robocode.util.Utils;
 
  
−
public void run() {
+
For even faster information collection, you should turn the gun (or even the robot base as well) in the same direction as the radar. Due to [[Robocode/Game Physics|Robocode game physics]], spinning the gun and radar at the same time will give your robot a 65° (20° + 45°) scan arc, instead of a 45° arc.
−
    // ...
 
  
−
    turnRadarRightRadians(Double.POSITIVE_INFINITY);
+
== 1-vs-1 radar ==
−
    do {
+
: ''Main article: [[One on One Radar]]
−
        // Check for new targets
+
One on one radars are the smallest of the bunch and many can get a scan in every turn, producing a perfect lock. This simplest lock is:
−
        scan();
 
−
    } while (true);
 
−
}
 
  
 +
<syntaxhighlight>
 
public void onScannedRobot(ScannedRobotEvent e) {
 
public void onScannedRobot(ScannedRobotEvent e) {
−
     double radarTurn =
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     setTurnRadarRight(2.0 * Utils.normalRelativeAngleDegrees(getHeading() + e.getBearing() - getRadarHeading()));
−
        // Absolute bearing to target
 
−
        getHeadingRadians() + e.getBearingRadians()
 
−
        // Subtract current radar heading to get turn required
 
−
        - getRadarHeadingRadians();
 
−
 
 
−
    setTurnRadarRightRadians(Utils.normalRelativeAngle(radarTurn));
 
−
 
 
−
    // ...
 
−
}
 
−
</pre>
 
−
 
 
−
The problem of the odd slippage can be resolved by multiplying the sweep angle by a factor, eg. factor*Utils.normalRelativeAngle(radarTurn)
 
−
* 1.0 Just gives the same behaviour as above.
 
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* 1.99 Gives a lock that slowly narrows down to the minimal necessary to stay on target.
 
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* 2.0 Keeps sweeping a little bit ahead and behind the target to stay locked on. This is factor which most top bot used.
 
−
 
 
−
==== Wide lock ====
 
−
The wide radar locks are used to avoid the rare slipping of the narrow lock. They scan a wider portion of the battlefield and will not slip. This type of lock is generally the largest of the 1-vs-1 radars.
 
−
 
 
−
Here is an example of this type of radar:
 
−
<pre>
 
−
import robocode.util.Utils;
 
−
 
 
−
public void run() {
 
−
    // ...
 
−
 
 
−
    while(true) {
 
−
        turnRadarRightRadians(Double.POSITIVE_INFINITY);
 
−
    }
 
 
}
 
}
 +
</syntaxhighlight>
  
−
public void onScannedRobot(ScannedRobotEvent e) {
+
Other types of [[One on One Radar|1v1 radar]] include the [[One on One Radar#Width Lock|width lock]] and the [[One on One Radar#The Infinity Lock|infinity lock]].
−
    double absoluteBearing = getHeadingRadians() + e.getBearingRadians();
 
−
    double radarTurn = Utils.normalRelativeAngle(absoluteBearing - getRadarHeadingRadians());
 
−
 
 
−
    // Width of the bot, plus twice the arc it can move in a tick, limit it to the max turn
 
−
    double arcToScan = Math.min(Math.atan(36.0 / e.getDistance()), PI/4.0);
 
−
 
 
−
    // We want to sent the radar even further in the direction it's moving
 
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    radarTurn += (radarTurn < 0) ? -arcToScan : arcToScan;
 
−
    setTurnRadarRightRadians(radarTurn);
 
−
 
 
−
    // ...
 
−
}
 
−
</pre>
 
  
 
== Melee radars ==
 
== Melee radars ==
−
Melee radars are more complex and take up considerable more room inside a robot. Since the field of opponents does not usually fall within a 45° area, compromises must be made between frequent data of one bot (e.g., the firing target) and consistently updated data of all bots.
+
: ''Main article: [[Melee Radar]]
−
 
+
Melee radars are more complex and take up considerably more room inside a robot. Since the field of opponents does not usually fall within a 45° area, compromises must be made between frequent data of one bot (e.g., the firing target) and consistently updated data of all bots. Common melee radars include:
−
=== Spinning radar ===
+
* Spinning radar ‒ Simple but inefficient.
−
Just as with one on one, there is the generic spinning radar. This is the most used melee radar as it is by far the easiest to implement.
+
* Oldest scanned radar ‒ Scan all bots, and then reverse (unless it would be more efficient to not do that). Probably good enough.
−
 
+
* Optimal radar ‒ Present in all top melee bots. Left as an exercise to the reader.
−
<pre>
+
* Gun heat lock ‒ Lock on a target before firing, spin otherwise. Some bots do this.
−
public void run() {
 
−
    // ...
 
−
 
 
−
    while(true) {
 
−
        turnRadarRightRadians(Double.POSITIVE_INFINITY);
 
−
    }
 
−
}
 
−
</pre>
 
−
 
 
−
==== Corner Arc ====
 
−
A variation on the spinning radar, if the robot is in a corner it scans back and forth across the 90 degree arc away from the corner, as not to waste time scanning where there cannot be any robots. Typically, this is used only in smaller melee robots, which do not ahve room for a more complicated radar system. Melee bots with room tend to use one of the implementations below.
 
−
 
 
−
=== Oldest Scanned ===
 
−
This type of melee radar spins towards the robot it hasn't seen in the longest amount of time. Here is an example of this type of radar.
 
−
<pre>
 
−
import java.util.*;
 
−
import robocode.*;
 
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import robocode.util.*;
 
−
 
 
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// ... Within robot class
 
−
 
 
−
static LinkedHashMap<String, Double> enemyHashMap;
 
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static double scanDir;
 
−
static Object sought;
 
−
 
 
−
public void run() {
 
−
    scanDir = 1;
 
−
    enemyHashMap = new LinkedHashMap<String, Double>(5, 2, true);
 
−
 
 
−
    // ...
 
−
 
 
−
    while(true) {
 
−
        setTurnRadarRightRadians(scanDir * Double.POSITIVE_INFINITY);
 
−
        scan();
 
−
    }
 
−
}
 
−
 
 
−
public void onRobotDeath(RobotDeathEvent e) {
 
−
    enemyHashMap.remove(e.getName());
 
−
    sought = null;
 
−
}
 
−
 
 
−
public void onScannedRobot(ScannedRobotEvent e) {
 
−
    String name = e.getName();
 
−
    LinkedHashMap<String, Double> ehm = enemyHashMap;
 
−
 
 
−
    ehm.put(name, getHeadingRadians() + e.getBearingRadians());
 
−
 
 
−
    if ((name == sought || sought == null) && ehm.size() == getOthers()) {
 
−
scanDir = Utils.normalRelativeAngle(ehm.values().iterator().next()
 
−
            - getRadarHeadingRadians());
 
−
        sought = ehm.keySet().iterator().next();
 
−
    }
 
−
 
 
−
    // ...
 
−
}
 
−
</pre>
 
−
With above code, the radar will spin passed every bot, and then reverse it's direction until passed all bots and repeat again. if spin take more than 4 ticks, Radar will continue spinning like spinning radar above. This kind of radar are use in many top bots include Shadow and Phoenix. I prefer you to use this kind of radar unless you need a melee radar lock or your targeting system require you to have enemy scan every 8 ticks.
 
−
 
 
−
=== Gun Heat Lock ===
 
−
A technique developed by [[Paul Evans]]/[[Kawagi]] for [[SandboxDT]]/[[FloodHT]]. This radar locks onto a target when the robot has low gunheat. Normally this is best for melee robots which use GuessFactor Targeting.
 
−
<pre>
 
−
 
 
−
public void run() {
 
−
    // ...
 
−
    setTurnRadarRightRadians(Double.POSITIVE_INFINITY);
 
−
}
 
−
 
 
−
public void onScannedRobot(ScannedRobotEvent e) {
 
−
    // ... your own target selection
 
−
    double absoluteBearing = getHeadingRadians() + e.getBearingRadians();
 
−
    if (isCurrentTarget && getGunHeat() < 0.5) { // Lock for 5 ticks
 
−
        setTurnRadarRightRadians(3.5 * Utils.normalRelativeAngle(absoluteBearing - getRadarHeadingRadians()));
 
−
    else
 
−
        setTurnRadarRightRadians(Double.POSITIVE_INFINITY);
 
−
}
 
−
</pre>
 
−
The code above uses a Narrow Lock but the simpler Infinity Lock works just as well. For a narrow lock, it is recommended you multiply by a large factor to continue scanning other robots while locked.
 
−
 
 
−
== Notes ==
 
−
For most of these radar locks, you will need to add one of the following to your <code>run()</code> method:
 
−
 
 
−
<pre>
 
−
setAdjustRadarForRobotTurn(true);
 
−
setAdjustGunForRobotTurn(true);
 
−
setAdjustRadarForGunTurn(true);
 
−
</pre>
 
−
 
 
−
[[Category:Code Snippets]]
 
−
[[th:เรดาร์]]
 

Latest revision as of 02:01, 28 August 2017

Radar in Robocode

Radar is one of the most vital components of your robot. Without it, targeting is effectively impossible and movement is purely random. Just as with movement and targeting, there are many simple and complex algorithms for radar control. In most robots the radar takes up the smallest portion of code.

Technical information

A radar in Robocode can turn a maximum of 45° or π/4 rad in a single tick. The radar scans robots up to 1200 units away. The angle that the radar rotates between two ticks creates what is called a radar arc, and every robot detected within the arc is sent to the onScannedRobot() method in order of distance from the scanning bot. The closest bot is detected first, while the furthest bot is detected last. By default, the onScannedRobot() method has the lowest event priority of all the event handlers in Robocode, so it is the last one to be triggered each tick.

Prerequisites

Before you start implementing a radar, you should have:

  1. Followed the My First Robot Tutorial, and created a robot.
  2. Read the FAQ, understood non-blocking calls, and switched your robot to an AdvancedRobot.
  3. Gotten a good understanding of Java and at least a basic familiarity of the Robocode API.

If you haven't done all of these, do them first. Otherwise, this article will only make you more confused.

Display scan arcs

By default, Robocode hides radar arcs, to prevent visual overload. This is a good idea in large melee battles, but not when debugging your radar.

Scan arcs can be enabled in Robocode's Preferences:

EnableScanArcs.png

Configure the radar

Your first action in run() should always be: 

setAdjustGunForRobotTurn(true);
setAdjustRadarForGunTurn(true);

This allows your robot's base, gun, and radar to rotate independently. It is practically essential for radar locks and any form of accurate targeting.

At round start

One of the first actions your robot performs should be to turn the radar as much as possible. A simple implementation would be: 

setTurnRadarRight(Double.POSITIVE_INFINITY);

This causes the radar to begin turning clockwise, forever. However, it may not be wise to always turn the radar clockwise. Sometimes, turning it counterclockwise might provide more information, faster. The optimal scan direction is the one with the shortest rotational difference to the angle between the robot and the battlefield center.

For even faster information collection, you should turn the gun (or even the robot base as well) in the same direction as the radar. Due to Robocode game physics, spinning the gun and radar at the same time will give your robot a 65° (20° + 45°) scan arc, instead of a 45° arc.

1-vs-1 radar

Main article: One on One Radar

One on one radars are the smallest of the bunch and many can get a scan in every turn, producing a perfect lock. This simplest lock is: 

public void onScannedRobot(ScannedRobotEvent e) {
    setTurnRadarRight(2.0 * Utils.normalRelativeAngleDegrees(getHeading() + e.getBearing() - getRadarHeading()));
}

Other types of 1v1 radar include the width lock and the infinity lock.

Melee radars

Main article: Melee Radar

Melee radars are more complex and take up considerably more room inside a robot. Since the field of opponents does not usually fall within a 45° area, compromises must be made between frequent data of one bot (e.g., the firing target) and consistently updated data of all bots. Common melee radars include:

  • Spinning radar ‒ Simple but inefficient.
  • Oldest scanned radar ‒ Scan all bots, and then reverse (unless it would be more efficient to not do that). Probably good enough.
  • Optimal radar ‒ Present in all top melee bots. Left as an exercise to the reader.
  • Gun heat lock ‒ Lock on a target before firing, spin otherwise. Some bots do this.
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