@ErAnushka • 24 Sep, 2012
Fore Bearing - Back Bearing = 180?

OR
Back Bearing - Fore Bearing = 180.

I fully understood the concept of meridian and bearing 😀

😲 But this thing is little confusing, as far as I know, Back Bearing - Fore Bearing should be 180, but I read somewhere that, Fore Bearing - Back Bearing = 180, but if you imagine, FB-BB would be negetive!

and let's say we have ABCD traverse,
Back bearing of AB line - Fore bearing of AB line = 180,

But if we go further and take the line DA,
Fore Bearing of DA - Back Bearing of DA = 180,

Now I don't understand, why some people fixed FB-BB = 180?
or my imagination is wrong ? What's the correct method and principle?

@Saiwal • 25 Sep, 2012 • 3 likes there is no absolute relation between the forebearing and backbearing.
Depending on the survey direction and location of north the following relation exists:
Fore bearing = Back bearing ± 180°
or
Back Bearing = Fore Bearing ± 180°

thus both your arguments are true.
refer: https://goo.gl/ql1p3
@Jeffrey Arulraj • 25 Sep, 2012 • 1 like We just use each one when the other is more than !80

If FB=350 then BB=FB-180=170

And if BB =350 then FB=BB-180=170
@ErAnushka • 25 Sep, 2012 • 1 like
Saiwal
there is no absolute relation between the forebearing and backbearing.
Depending on the survey direction and location of north the following relation exists:
Fore bearing = Back bearing ± 180°
or
Back Bearing = Fore Bearing ± 180°

thus both your arguments are true.
refer: https://goo.gl/ql1p3
You saved my day! ☕ Thank you ^_^
@ErAnushka • 25 Sep, 2012
jeffrey samuel
We just use each one when the other is more than !80

If FB=350 then BB=FB-180=170

And if BB =350 then FB=BB-180=170
I got it ^_^ Thank you 😀
@Jeffrey Arulraj • 26 Sep, 2012 • 1 like Most welcome pal
@Rock Rohit • 13 Oct, 2015 If fb is 145 then what will be the BB
@Vinay Mishra • 25 Jan, 2020 • 3 likes

The relation is:

FB = BB ± 180 ('+' sign when BB is less than 180 and '-' sign when BB is more than 180).

BB = FB ± 180 ('+' sign when FB is less than 180 and '-' sign when FB is more than 180).

If FB is 145 then BB will be 325.

@bill yorke • 25 Jan, 2020 • 1 like

No major variation exists between fore bearing and back bearing. Direction of survey and location of the north however guides the relation between back bearing and fore bearing based on the reference point.

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