I'm not sure if this is the right forum to ask this question but here it goes: I'm trying to write a program that simulates an old but simple target tracking device used on ships in WWII but I've been having problems trying to understand how to use a few geometrical equations in a code.
The program should be able to come up with new ranges and bearings over time based on initial values.
Here are the equations in question, pgs 24-25 of this 1944 manual:
http://www.hnsa.org/doc/tdc/pg024.htm
http://www.hnsa.org/doc/tdc/pg025.htm
The terminology for the variables can be found here on pgs. 13/15:
http://www.hnsa.org/doc/tdc/pg013.htm
http://www.hnsa.org/doc/tdc/pg015.htm
I'm trying to figure out how to calculate delta R from equation VIII on pg25 and delta B equation X on pg25.
This is the "wrong" quick code I came up with in C# for testing (I'm sure I'm missing something):
- Code: Select all
public partial class Form1 : Form
{
float R, B, So, St, Co, Ct, A, Br, iR, iB;
float dR, dB, dt;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
//********** RANGES
iR = 5000; // Initial range in yards
R = iR; // Range
//********* COURSES AND SPEEDS
Ct = 120; // Target course in degrees
St = 10 * 0.5626f; // Target speed in knots (converted to yards/sec)
Co = 270; // Ownship course
So = 5 * 0.5626f; // Ownship speed in knots (converted to yards/sec)
//************** ANGLES
Br = 25; // Relative target bearing
iB = Co + Br; // Initial true target bearing in degrees
B = iB; // True target bearing
A = 180 + B - Ct; // Target angle
//********** INSTANTANEOUS CHANGES
dB = 0; // Instantaneous change in true bearing
dR = 0; // Instantaneous change in range
dt = 1f; // time step?
for (float t = 1f; t < 1000f; t += dt)
{
dR = dR + (St * (float)Math.Cos(DegToRad(A)) + So * (float)Math.Cos(DegToRad(Br)));
R = iR - dR;
dB = dB + ((St * (float)Math.Sin(DegToRad(A)) + So * (float)Math.Sin(DegToRad(Br)))*t) / R;
B = iB + dB;
if (B > 360)
B = B % 360;
if (B < 0)
B = B + 360;
if (B > 359.5 && B < 360.5)
B = 0;
Br = B - Co;
if (Br > 360)
Br = Br % 360;
if (Br < 0)
Br = Br + 360;
if (Br > 359.5 && Br < 360.5)
Br = 0;
A = 180 + B - Ct;
if (A > 360)
A = A % 360;
if (A < 0)
A = A + 360;
if (A > 359.5 && A < 360.5)
A = 0;
listBox1.Items.Add( "t = " + t.ToString("000.00") + " Range (R) = " + R.ToString("0000") + " True Bearing (B) = " + B.ToString("000.00")
+ " Relative Bearing (Br) = " + Br.ToString("000.00") + " Angle A = " + A.ToString("000.00") + " dB = " + dB.ToString("0.0000")
+ " dR = " + dR.ToString("0.0000"));
}
}
double DegToRad(float dd) { return (double)(0.0174532925f * dd); }
}
But once I run some of these test problems:
http://www.hnsa.org/doc/tdc/pg220.htm
...the new range and bearing results aren't even close to the values shown.
What I'm not understanding is how to integrate the equations over time and how to keep track of time in seconds or minutes(not in real time I mean). If any of you guys have ideas on how to correctly code these equations (in C# or any other language) I'd really appreciate!
I'm sorry if this seems like a very basic question, but I'm just not seeing how to solve it.
Thanks!
