fgdata/Aircraft/Instruments-3d/radardist/radardist.nas

### Radar Visibility Calculator

# Jettoo (glazmax) and xiii (Alexis)

# my_maxrange(myaircraft): finds our own aircraft max radar range in a table.
# Returns my_radarcorr in kilometers, should be called from your own aircraft
# radar stuff.

# radis(i, my_radarcorr): find multiplayer[i], its Radar Cross Section (RCS),
# applies factor upon our altitude, shorter radar detection distance (due to air
# turbulence), then factor upon its altitude above ground, and finaly computes if
# it is detectable given our radar range.
# Returns 1 if detectable, 0 if not. Should be called from your own aircraft
# radar stuff too.

var data_path = getprop("/sim/fg-root") ~ "/Aircraft/Instruments-3d/radardist/radardist.xml";
var aircraftData = {};
var radarData = [];

mpnode_string = nil;
var cutname   = nil;
var mpnode    = nil;
var mpname_node_string = nil;
var mpname_node = nil;
var mpname    = nil;
var splitname = nil;
var acname    = nil;
var rcs_4r    = nil; 
var radartype = nil; 
var alt_corr  = nil; 
var alt_ac    = nil; 
var agl_corr  = nil; 
var mp_lon    = nil; 
var mp_lat    = nil; 
var pos_elev  = nil; 
var mp_agl    = nil; 
var det_range = nil; 
var act_range = nil;
var max_range = nil;
var radar_range = nil;
var radar_area = nil;
var have_radar = nil;

var FT2M = 0.3048;
var NM2KM = 1.852;

var my_maxrange = func(a) {
	max_range = 0;
	radar_range = 0;
	radar_area = 0;
	acname = aircraftData[a] or 0;
	if ( acname ) {
		have_radar = radarData[acname][4];
		if ( have_radar != "none" and  have_radar != "unknown") {
			radar_area = radarData[acname][7];
			radar_range = radarData[acname][5];
			if ( radar_area > 0 ) { max_range = radar_range / radar_area }
		}
	}
	return( max_range );
}

var get_ecm_type_num = func(a) {
	acname = aircraftData[a] or 0;
	var num = 0;
	if ( acname ) {
		num = radarData[acname][8];
	}
	return( num );
} 

var get_aircraft_name = func( t ) {
	# Get the multiplayer aircraft name.
	mpnode_string = t;
	mpnode =  props.globals.getNode(mpnode_string);
	if ( find("tanker", mpnode_string) > 0 ) {
		cutname = "KC135";
	} else {
		mpname_node_string = mpnode_string ~ "/sim/model/path";
		mpname_node = props.globals.getNode(mpname_node_string);
		if (mpname_node == nil) { return(0) }

		var mpname = mpname_node.getValue();
		if (mpname == nil) { return(0) }

		splitname = split("/", mpname);
		cutname = splitname[1];
		
	}
	return( cutname );
}


var radis = func(t, my_radarcorr) {
	cutname = get_aircraft_name(t);
	# Calculate the rcs detection range,
	# if aircraft is not found in list, 0 (generic) will be used.
	acname = aircraftData[cutname];
	if ( acname == nil ) { acname = 0 }
	rcs_4r = radarData[acname][3];

	# Add a correction factor for altitude, as lower alt means
	# shorter radar distance (due to air turbulence).
	alt_corr = 1;
	alt_ac = mpnode.getNode("position/altitude-ft").getValue();
	if (alt_ac <= 1000) {
		alt_corr = 0.6;
	} elsif ((alt_ac > 1000) and (alt_ac <= 5000)) {
		alt_corr = 0.8;
	}
	# Add a correction factor for altitude AGL. Skip if AI tanker.
	agl_corr = 1;
	if ( find("tanker", t) == 0 ) {
		mp_lon = mpnode.getNode("position/longitude-deg").getValue();
		pos_elev = geo.elevation(mp_lat, mp_lon);
		if (pos_elev != nil) {
			mp_agl = alt_ac - ( pos_elev / FT2M );
			if (mp_agl <= 40) {
				agl_corr = 0.03;
			} elsif ((mp_agl > 40) and (mp_agl <= 80)) {
				agl_corr = 0.07;
			} elsif ((mp_agl > 80) and (mp_agl <= 120)) {
				agl_corr = 0.25;
			} elsif ((mp_agl > 120) and (mp_agl <= 300)) {
				agl_corr = 0.4;
			} elsif ((mp_agl > 300) and (mp_agl <= 600)) {
				agl_corr = 0.7;
			} elsif ((mp_agl > 600) and (mp_agl <= 1000)) {
				agl_corr = 0.85;
			}
		}
	}
	# Calculate the detection distance for this multiplayer.
	det_range = my_radarcorr * rcs_4r * alt_corr * agl_corr / NM2KM;

	# Compare if aircraft is in detection range and return.
	act_range = mpnode.getNode("radar/range-nm").getValue() or 500;
	if (det_range >= act_range) {
		return(1);
	}
	return(0);
}

var radar_horizon = func(our_alt_ft, target_alt_ft) {
	if (our_alt_ft < 0 or our_alt_ft == nil) { our_alt_ft = 0 }
	if (target_alt_ft < 0 or target_alt_ft == nil) { target_alt_ft = 0 }
	return( 2.2 * ( math.sqrt(our_alt_ft * FT2M) + math.sqrt(target_alt_ft * FT2M) ) );
}


var load_data = func {
	# a) converts aircraft model name to lookup (index) number in aircraftData{}.
	# b) appends ordered list of data into radarData[],
	# data is:
	# - acname (the index number)
	# - the first (if several) aircraft model name corresponding to this type,
	# - RCS(m2),
	# - 4th root of RCS,
	# - radar type,
	# - max. radar range(km),
	# - max. radar range target seize(RCS)m2,
	# - 4th root of radar RCS.
	var data_node = props.globals.getNode("instrumentation/radar-performance/data");
	var aircraft_types = data_node.getChildren();
	foreach( var t; aircraft_types ) {
		var index = t.getIndex();
		var aircraft_names = t.getChildren();
		foreach( var n; aircraft_names) {
			if ( n.getName() == "name") {
				aircraftData[n.getValue()] = index;
			}
		}
		var t_list = [
			index,
			t.getNode("name[0]").getValue(),
			t.getNode("rcs-sq-meter").getValue(),
			t.getNode("rcs-4th-root").getValue(),
			t.getNode("radar-type").getValue(),
			t.getNode("max-radar-rng-km").getValue(),
			t.getNode("max-target-sq-meter").getValue(),
			t.getNode("max-target-4th-root").getValue(),
			t.getNode("ecm-type-num").getValue()
		];
		append(radarData, t_list);
	}
}


var init = func {
	print("Initializing Radar Data");
	io.read_properties(data_path, props.globals);
	load_data();
}