Four bearings while moving, with variable time intervals

Efshapo · 08-05-21, 06:22 PM

Hello everyone!

I developed a graphical method to get target data using four bearings while moving. The new thing is that it does not require time intervals to be constant.

You can find a tuto here: 4 Bearings, Moving, Variable Time Intervals

Do you know if something similar exist? I mean, beside usual TMA that requires a lot of maths, something graphical and simple.

derstosstrupp · 08-05-21, 07:02 PM

I can’t say I’ve seen any versions put out there with unequal time intervals, this is very novel. I’m not sure it’s simpler, but I think you’ve laid it out well. Putting my personal feelings about the 4-bearing method aside, I think you’ve done a good job here.

Efshapo · 08-07-21, 01:03 AM

Ok, thanks!

And I think we agree on the lack of practicality of the 4-bearing method. :]
I just find the exercise kinda fun. Also, it can be useful with the hydrophone, when the convoy is not in sight. That rarely happens in WP though.

By the way, I'm not saying it is simpler to do the 4-bearing method this way, I'm saying it's the simplest way I found to do it with variable time intervals.

Variable time intervals is a cool feature though, because it's more flexible. Here are some of the advantages from the top of my head:
- You can take your time to do an accurate bearing measurement (E.g. at a round angle value) and then note the exact time it was done, without the need to do it at a specific moment.
- You can also re-do any measurement if you find out it has been done at a bad position (E.g. close to a singularity) without having to ditch all the previous work.

ljqcn101 · 08-08-21, 12:31 AM

Elegant!

So I was actually using the fixed interval version of this method (the first half) for a long time? (https://www.subsim.com/radioroom/sho...d.php?t=240883)

I guess the philosophy is to find out the segments that are of the same ratio as time intervals.

Pisces · 08-08-21, 06:32 AM

Yes, this method is quite elegant. You are doing 2 times 2 the same procedure. Although it may be a lengthy procedure, it's routine procedure all around. No need for choosing a particular bearing-line to do further geometrical constructions that looks more usefull than others.

First starting with a near and far assumption on position on the first bearing. Then choose a point on the second bearing to assume a target course (for that particular case). Then these are projected forward to the 3rd bearing time and target course corrected (for that particular case) to find the point on the 3rd bearing (using the parallel of the 1st bearing) that satisfies the constant target speed across the 3 bearings at that distance. From those 2 near and far lines you predict the point of the locusline for the time of the 4th bearing. The target has to be somewhere on that line at the 4th bearing time depending on the initial unknown distance. Then the position of the target at the time of the 4th bearing is fixed by the actual 4th bearing intersecting the locusline.

To find the position of the target at the time of the 1st bearing Efshapo does the same thing in reverse, starting from the 4th back to the first. Then he fixes the line through the 2 points which is the target course. And the overall distance between them, or the intermediate bearing intersections, indicate the target speed.

Sean C · 08-08-21, 07:53 AM

08-05-21, 06:22 PM	#1
Efshapo Watch Join Date: May 2021 Location: France Posts: 29 Downloads: 3 Uploads: 0	Four bearings while moving, with variable time intervals Hello everyone! I developed a graphical method to get target data using four bearings while moving. The new thing is that it does not require time intervals to be constant. You can find a tuto here: 4 Bearings, Moving, Variable Time Intervals Do you know if something similar exist? I mean, beside usual TMA that requires a lot of maths, something graphical and simple. Last edited by Efshapo; 11-17-21 at 04:13 AM.

08-05-21, 07:02 PM	#2
derstosstrupp Grey Wolf Join Date: Aug 2008 Posts: 883 Downloads: 489 Uploads: 0	I can’t say I’ve seen any versions put out there with unequal time intervals, this is very novel. I’m not sure it’s simpler, but I think you’ve laid it out well. Putting my personal feelings about the 4-bearing method aside, I think you’ve done a good job here. __________________ Ask me anything about the Type VII or IX! One-Stop Targeting Shop: https://drive.google.com/drive/folde...WwBt-1vjW28JbO My YT Channel: https://www.youtube.com/channel/UCIJ...9FXbD3S2kgwdPQ

08-08-21, 12:31 AM	#4
ljqcn101 Sailor man Join Date: Jan 2013 Location: Hong Kong Posts: 50 Downloads: 78 Uploads: 3	Elegant! So I was actually using the fixed interval version of this method (the first half) for a long time? (https://www.subsim.com/radioroom/sho...d.php?t=240883) I guess the philosophy is to find out the segments that are of the same ratio as time intervals. __________________ Automatic TMA calculator (metric system) Automatic TMA line detector and solver for DW/SC/688i Automatic TMA line detector and solver for maneuvering target (new) Last edited by ljqcn101; 08-08-21 at 12:54 AM.

08-08-21, 06:32 AM	#5
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,892 Downloads: 300 Uploads: 0	Yes, this method is quite elegant. You are doing 2 times 2 the same procedure. Although it may be a lengthy procedure, it's routine procedure all around. No need for choosing a particular bearing-line to do further geometrical constructions that looks more usefull than others. First starting with a near and far assumption on position on the first bearing. Then choose a point on the second bearing to assume a target course (for that particular case). Then these are projected forward to the 3rd bearing time and target course corrected (for that particular case) to find the point on the 3rd bearing (using the parallel of the 1st bearing) that satisfies the constant target speed across the 3 bearings at that distance. From those 2 near and far lines you predict the point of the locusline for the time of the 4th bearing. The target has to be somewhere on that line at the 4th bearing time depending on the initial unknown distance. Then the position of the target at the time of the 4th bearing is fixed by the actual 4th bearing intersecting the locusline. To find the position of the target at the time of the 1st bearing Efshapo does the same thing in reverse, starting from the 4th back to the first. Then he fixes the line through the 2 points which is the target course. And the overall distance between them, or the intermediate bearing intersections, indicate the target speed. __________________ My site downloads: https://ricojansen.nl/downloads

08-08-21, 07:53 AM	#6
Sean C Grey Wolf Join Date: Jun 2017 Location: Norfolk, VA Posts: 906 Downloads: 12 Uploads: 2	You might be interested in this: __________________ If you have a question about celestial navigation ... ask me! Celestial Navigation Spreadsheet

08-07-21, 01:03 AM	#3
Efshapo Watch Join Date: May 2021 Location: France Posts: 29 Downloads: 3 Uploads: 0	Ok, thanks! And I think we agree on the lack of practicality of the 4-bearing method. :] I just find the exercise kinda fun. Also, it can be useful with the hydrophone, when the convoy is not in sight. That rarely happens in WP though. By the way, I'm not saying it is simpler to do the 4-bearing method this way, I'm saying it's the simplest way I found to do it with variable time intervals. Variable time intervals is a cool feature though, because it's more flexible. Here are some of the advantages from the top of my head: - You can take your time to do an accurate bearing measurement (E.g. at a round angle value) and then note the exact time it was done, without the need to do it at a specific moment. - You can also re-do any measurement if you find out it has been done at a bad position (E.g. close to a singularity) without having to ditch all the previous work.