extern void object::Defend()
{
    int enemyType = AlienAnt;      // put enemy category here (i.e. AlienWorm)
    int parimeterToScan = 50;      // adjust value to look farther if needed 
	
    point campSpot = position;     // position/spot to defend (default origin)
    int maxDistFromCampSpot = 10;  // patrol radius
	
    object enemy;
	
    while(true)
    {
        enemy = radar(enemyType,0,360,0,parimeterToScan);

        if(enemy == null)                                     // if no enemy around 
            basicMaintE();                                    // fill up on energy if needed 
        else
            moveAndDestroy(enemy);                            // otherwise attack
		
        enemy = radar(enemyType,0,360,0,parimeterToScan);     // between recharging, enemy spotted?

        if(enemy == null)                                     // if no enemy around 
             basicMaintS();                                   // fill up on shields if needed
        else
	     moveAndDestroy(enemy);                           // otherwise attack
		
        enemy = radar(enemyType,0,360,0,parimeterToScan);     // between recharging, enemy spotted?

	if(enemy == null)                                     // if no further enemies around
	    getBackToPosition(campSpot,maxDistFromCampSpot);  // move back into position
        else
           moveAndDestroy(enemy);                             // otherwise attack
    }
	
}

void object::basicMaintE()                             // basic energy maintenance
{
    if(energyCell.energyLevel < 0.5)                   // adjust energy tolerance here
    {
        object power;
		
        if( (power = radar(PowerStation)) != null )    // if there is a powerstation
        {
            goto(power.position);                      // go there
            while(energyCell.energyLevel < 1)          // and fill up
                wait(1);
        }
    }
}  

void object::basicMaintS()                             // basic shield maintenance
{
    if(shieldLevel < 0.8)                              // adjust shield tolerance here
    {
        object repair; 
		
        if( (repair = radar(RepairCenter)) != null )   // if there is a repaircenter
        {
            goto(repair.position);                     // go there
            while(shieldLevel < 1)                     // and get repaired
                wait(1);
        }
    }
}

void object::getBackToPosition(point pos, int parimeter)
{ 
    float dis = distance(position,pos);
	
    if(dis > parimeter)                  // if outside of patrol radius
    {
        float dif = pos.z-position.z;
        float ang = asin(dif/dis);
		
        jet(1-(ang/-20));
		
        float dir = direction(pos);
		
        motor(1-dir/22.5,1+dir/22.5);    // move back into position
    }
	
    else
    {
        motor(0,0);                      // otherwise camp
        if(topo(position) > 0)           // if groundlevel is above water
            jet(-1);                     // then it's safe to land
    }
}

void object::moveAndDestroy(object target)
{
    float dir;    // direction of target from shooter
    float dis;    // distance of target from shooter
    float dif;    // difference in altitude of target & shooter (relative to sea-level)
    float ang;    // angle shooter must aim (-20 degrees favorable)
	
    dis = distance(position,target.position);
    dif = target.position.z-position.z;
    ang = asin(dif/dis);
	
    jet(1-(ang/-20));                         // thrust until 20 degress above target
	
    dir = direction(target.position); 
	
    motor(1-dir/22.5,1+dir/22.5);             // move towards enemy
	
    dis = distance(position,target.position);   
    dif = target.position.z-position.z;         
    ang = asin(dif/dis);                        
	
    aim(ang);                                 // take aim
	
    dir = direction(target.position);           
	
    if(dis < 30 and dir > -10 and dir < 10)   // if within range
        fire(0.1);
}