SUBSIM Radio Room Forums - View Single Post

Pisces · 10-14-09, 03:54 PM

Platapus: Did you notice he placed text descriptions of what and why he did things? He used circles to determine where all points are that are equal distances (constant speed over equal time interval) away from the center. He starts of with a random line as a guess on the course (and range and speed) of the target. Then he uses the circle to prove it is wrong because the 3rd bearing doesn't intersect the same point as where the circle and random line intersect. Then he uses two protractor tools (118 degrees drawn between bearing 1 and the guessed course) to effectively make a line parallel to bearing 1 that does go through the circle and guessed courseline. Then he locates where the parallel bearingline and the real 3rd bearing line intersect. That point, and the center of the circle on bearing 2, define the direction or course of the target. (But not the range and speed!, because those 2 are proportionally related. You need a different point of view to 'fix' that.) Anyway, he first corrects the guessed course into this new course and extends the true course line back to bearing 1. And also expands the circle and direction of the radius arrow to match that. Then he cleans up the plot, erasing: the guessed course, the aiding protractor tools, and finally the circle. And also added marks on the established bearingline intersections. (I personally would have left the circle on the map, pointing the arrow in the direction of the target's course to avoid Bernard situations. As the points where the marks are are not confirmed by range, just points that define the course in relation to the bearings. It makes them look more real positions than they are. But that's just me.)

To predict where the sound comes from at the time of bearing 4 he re-creates the circle and moves it up to the mark on bearing 3 and extends the course line again to create the intersection of the predicted bearing 4. Again, the circle is used to keep 2 points equally far away from the center, and on the same line diametrically opposed. Then he plot's a predicted 4th bearingline through it from the listening location. In the mean time he ordered course and speed to sprint away from his listening location.

Is that enough to get you back on track?

PL_Cmd_Jacek: If you move just a knot or so in the direction of the sound when you are waiting to take the first 3 bearings, then it would have minimal effect on the result. The drift of the sound bearing is primarily due to speed vector-components perpendicular to the bearing. If you move slowly and roughly along the bearingline you generate a very small, probably insignificant, perpendicular speed vector-component yourself. Just keep a steady course so you do not mess up you bearing measurments. Ideally you would want to use true bearings. But the game only reports relative bearings, so they need to have some reference direction that doesn't turn as you go.

EDIT: this might help the both of you to solve your questions: http://www.filefront.com/13598315/bearingsonly-TMA.pdf This technique uses essentially the same drawing to determine the course (relative motion), except it 'guesses' with a course perpendicular to bearing 1. Determining speed and range is quite different though. Just keep in mind, if your sub is hardly moving at all, his speed and course creates pretty much all the relative motion there is.

10-14-09, 03:54 PM	#24
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,892 Downloads: 300 Uploads: 0	Platapus: Did you notice he placed text descriptions of what and why he did things? He used circles to determine where all points are that are equal distances (constant speed over equal time interval) away from the center. He starts of with a random line as a guess on the course (and range and speed) of the target. Then he uses the circle to prove it is wrong because the 3rd bearing doesn't intersect the same point as where the circle and random line intersect. Then he uses two protractor tools (118 degrees drawn between bearing 1 and the guessed course) to effectively make a line parallel to bearing 1 that does go through the circle and guessed courseline. Then he locates where the parallel bearingline and the real 3rd bearing line intersect. That point, and the center of the circle on bearing 2, define the direction or course of the target. (But not the range and speed!, because those 2 are proportionally related. You need a different point of view to 'fix' that.) Anyway, he first corrects the guessed course into this new course and extends the true course line back to bearing 1. And also expands the circle and direction of the radius arrow to match that. Then he cleans up the plot, erasing: the guessed course, the aiding protractor tools, and finally the circle. And also added marks on the established bearingline intersections. (I personally would have left the circle on the map, pointing the arrow in the direction of the target's course to avoid Bernard situations. As the points where the marks are are not confirmed by range, just points that define the course in relation to the bearings. It makes them look more real positions than they are. But that's just me.) To predict where the sound comes from at the time of bearing 4 he re-creates the circle and moves it up to the mark on bearing 3 and extends the course line again to create the intersection of the predicted bearing 4. Again, the circle is used to keep 2 points equally far away from the center, and on the same line diametrically opposed. Then he plot's a predicted 4th bearingline through it from the listening location. In the mean time he ordered course and speed to sprint away from his listening location. Is that enough to get you back on track? PL_Cmd_Jacek: If you move just a knot or so in the direction of the sound when you are waiting to take the first 3 bearings, then it would have minimal effect on the result. The drift of the sound bearing is primarily due to speed vector-components perpendicular to the bearing. If you move slowly and roughly along the bearingline you generate a very small, probably insignificant, perpendicular speed vector-component yourself. Just keep a steady course so you do not mess up you bearing measurments. Ideally you would want to use true bearings. But the game only reports relative bearings, so they need to have some reference direction that doesn't turn as you go. EDIT: this might help the both of you to solve your questions: http://www.filefront.com/13598315/bearingsonly-TMA.pdf This technique uses essentially the same drawing to determine the course (relative motion), except it 'guesses' with a course perpendicular to bearing 1. Determining speed and range is quite different though. Just keep in mind, if your sub is hardly moving at all, his speed and course creates pretty much all the relative motion there is. __________________ My site downloads: https://ricojansen.nl/downloads Last edited by Pisces; 10-14-09 at 04:12 PM.