Editing revision 20 of Radar/RadarBot

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Here's a bot implementing an effective OneOnOne radar, without regard to CodeSize. In [[Melee]] it will simply spin. Many good melee bots uses a simple spinning radar like that. If I remember correctly even the mighty TheArtOfWar. -- [[PEZ]]
<pre>
public class RadarBot extends AdvancedRobot {
    private int timeSinceLastScan = 10;
    static double enemyAbsoluteBearing;

do {
        doScanner();
        execute();
    } while true;

public void onScannedRobot(ScannedRobotEvent e) {
        enemyAbsoluteBearing = getHeadingRadians() + e.getBearingRadians();
        timeSinceLastScan = 0;
    }

private void doScanner() {
        timeSinceLastScan++;
        double radarOffset = Double.POSITIVE_INFINITY;
        if(getOthers() == 1 && timeSinceLastScan < 3) {
            radarOffset = robocode.util.Utils.normalRelativeAngle(getRadarHeadingRadians() - enemyAbsoluteBearing);
            radarOffset += sign(radarOffset) * 0.02;
        }
        setTurnRadarLeftRadians(radarOffset);
    }

int sign(double v) {
        return v > 0 ? 1 : -1;
    }
}
</pre>
This is not by any means a radar meant for minibots since it consumes way to much codesize for that. Still, it's the radar used by [[Tityus]], which leaves some room for imporvement of that bot. -- [[PEZ]]

Thanks for the code example pez, this will be easy enough to get into my Micro, I have like 150 codesize to burn :) but I know I should shrink some of the stuff I have down. It isnt very compressed as it is. -- Dan724

why do you need to keep track of "<nowiki>timeSinceLastScan</nowiki>" ? --[[SSO]]

Sometimes the radar "slips" and then I need to spin the radar full turn. Or that's the theory. I have not tried without this. Does it work? -- [[PEZ]]

If you don't do that, you need to account for the beginning of the round. -- [[Kawigi]]

What does the sign function do?  I'm not familiar with the syntax. Thanks. -- [[Tango]]

It just returns '''1''' for positive numbers and '''-1''' for negative numbers or zero. It's good for knowing in what "direction" this or that observation is going. -- [[PEZ]]

Is that some kind of special java short version of if/then/else? :-/ I really should learn java properly... -- [[Tango]]

You could see it as a short for if/then/else. But it's nothing specifically Java about it. The function is actually defined last in that code snippet. Look closer. =) I would say that it's more a math thing if it wasn't that I think you should return zero for a zero value then. I could have used an if/then/else structure, but I don't think it would have been as readable. -- [[PEZ]]

I was looking at the function definition.  I just don't recognise the syntax with question marks and colons and suchlike. :-/ As i say, i should probably learn java. -- [[Tango]]

Ah! Sorry, I misunderstood the question. The question-mark and colon is sort-of a Java short for if/then/else indeed. It's called the trinary condition operator. It's inherited from C. Since lots and lots of programming languages take a lot of inspiration from the C syntax this operator exists in many languages. A similar thingy exists in the macro language of Excel if you are more familiar with that. There it's a function "immediate if()" named IIF(''condition'', ''result-if-true'', ''result-if-false''). So you read the statement in that sign() function like so: "If the value ''v" is greater than 0 - return 1, else return -1. -- [[PEZ]]

Unlike an if/then/else this does not /do/ anything, it merely selects between which of two values to "show" to the statement outside it. Ie:
<pre>if(blah) do_something();</pre> is legal.
<pre>blah?do_something:do_somethingelse();</pre> is not, unless do_something() and do_somethingelse() return values, and even then the trinary condition needs to be assigned somewhere, it can't be a standalone statement. -- [[Kuuran]]

Anyone thought of squeezing the code into a smaller space? :
<pre>
    private void doScanner() {
        timeSinceLastScan++;
        double radaroffset = ((getOthers() == 1 && timeSinceLastScan < 3)?robocode.util.Utils.normalRelativeAngle(getRadarHeadingRadians() - enemyAbsoluteBearing):Double.POSITIVE_INFINITY)<0);
        setTurnRadarLeftRadians(radaroffset * (radaroffset > 0 ? 1.02 : 0.98 ));
    }
</pre>

-- [[nfwu]]

I do not think this is smaller in codesize, and certainly not more readable. -- [[GrubbmGait]]

I mainly use a radar that determines how much it should turn to be exactly aimed at the enemy and then add a few degrees to keep it from slipping. I have only seen it completely slip once or twice (I do have some anti-radar slip code so that accounts for a few). I am not sure about the exact codesize but it is around 80. Of course the following code is the core of mine but...
<pre>
	double turnRadar = Utils.normalRelativeAngle(Utils.angleFromPoint(myX, myY, enemyX, enemyY) - radarHeading);
	if (others == 1)
		turnRadar += ((turnRadar >= 0)? 2: -2);
	else
		turnRadar += ((turnRadar >= 0)? 45: -45);
	return turnRadar;
</pre>

It does not work to well for melee but the if statement can be changed from having a very large angle to spinning like this:
<pre>
	double turnRadar = Utils.normalRelativeAngle(Utils.angleFromPoint(myX, myY, enemyX, enemyY) - radarHeading);
	if (others == 1)
		turnRadar += ((turnRadar >= 0)? 2: -2);
	else
		turnRadar = 360;
	return turnRadar;
</pre>

(Note: The code uses degrees.)

-- [[Kinsen]]

Summary:
Consciousness check: 10 * 10 =
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