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# Changes

## User:Necolatis/terrain detection from nasal

, 02:20, 5 January 2017
Second example
print("The planes has clear view of each other");
}
}
</syntaxhighlight>

== Find terrain from radar beam==
In this example, we have a Mig21 with a forward down looking terrain detecting radar.
The radar beam is fixed 15 degs down from the nose of the aircraft.
<syntaxhighlight lang="nasal">
# First we need this helper method:
var getGPS = func(x, y, z) {
#
# get Coord from body structural position. x,y,z must be in meters.
# derived from Vivian's code in AIModel/submodel.cxx.
#
var ac = geo.aircraft_position();

if(x == 0 and y==0 and z==0) {
return geo.Coord.new(ac);
}

var ac_roll = getprop("orientation/roll-deg");
var ac_pitch = getprop("orientation/pitch-deg");

var in = [0,0,0];
var trans = [[0,0,0],[0,0,0],[0,0,0]];
var out = [0,0,0];

in[0] = -x * M2FT;
in[1] = y * M2FT;
in[2] = z * M2FT;
# Pre-process trig functions:
var cosRx = math.cos(-ac_roll * D2R);
var sinRx = math.sin(-ac_roll * D2R);
var cosRy = math.cos(-ac_pitch * D2R);
var sinRy = math.sin(-ac_pitch * D2R);
var cosRz = math.cos(ac_hdg * D2R);
var sinRz = math.sin(ac_hdg * D2R);
# Set up the transform matrix:
trans[0][0] = cosRy * cosRz;
trans[0][1] = -1 * cosRx * sinRz + sinRx * sinRy * cosRz ;
trans[0][2] = sinRx * sinRz + cosRx * sinRy * cosRz;
trans[1][0] = cosRy * sinRz;
trans[1][1] = cosRx * cosRz + sinRx * sinRy * sinRz;
trans[1][2] = -1 * sinRx * cosRx + cosRx * sinRy * sinRz;
trans[2][0] = -1 * sinRy;
trans[2][1] = sinRx * cosRy;
trans[2][2] = cosRx * cosRy;
# Multiply the input and transform matrices:
out[0] = in[0] * trans[0][0] + in[1] * trans[0][1] + in[2] * trans[0][2];
out[1] = in[0] * trans[1][0] + in[1] * trans[1][1] + in[2] * trans[1][2];
out[2] = in[0] * trans[2][0] + in[1] * trans[2][1] + in[2] * trans[2][2];
# Convert ft to degrees of latitude:
out[0] = out[0] / (366468.96 - 3717.12 * math.cos(ac.lat() * D2R));
# Convert ft to degrees of longitude:
out[1] = out[1] / (365228.16 * math.cos(ac.lat() * D2R));
# Set position:
var mlat = ac.lat() + out[0];
var mlon = ac.lon() + out[1];
var malt = (ac.alt() * M2FT) + out[2];
var c = geo.Coord.new();
c.set_latlon(mlat, mlon, malt * FT2M);

return c;
}

#in this example we will just assume the radar is at the center of aircraft, thats pretty trivial to change though.
var myPos = geo.aircraft_position();

#first find a coord in the radar beam in aircraft coordinates:
var beam_x = -5000*math.cos(-15*D2R);#15 deg down, 5Km out
var beam_y = 0;
var beam_z = 5000*math.sin(-15*D2R);
var beam = getGPS(beam_x, beam_y, beam_z);

#we now find the vector the beam is pointed in:
v = get_cart_ground_intersection(myPos.x(), myPos.y(), myPos.z(), beam.x()-myPos.x(), beam.y()-myPos.y(), beam.z()-myPos.z());
if (v == nil) {
printf("No terrain");
} else {
var terrain = geo.Coord.new();
terrain.set_xyz(v[0],v[1],v[2]);
var terrainDist = myPos.direct_distance_to(terrain);
printf("terrain found %0.1f meters down the beam", terrainDist);
}
</syntaxhighlight>
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edits