Author Topic: Practicalities of compass and map navigation  (Read 2575 times)

GoneWest

  • Full Member
  • ***
  • Posts: 122
Re: Practicalities of compass and map navigation
« Reply #30 on: 13:54:51, 27/08/20 »
If you can navigate with a hand held compass to an accuracy of less than 5 degrees I'd be amazed. In my youth I was a national level orienteer, and did lots of detailed navigation in the Army, 5 degrees was always the quoted accuracy variation.


I'm not sure what others were talking about but the variation I was referring to was between grid north and magnetic north, true north is never considered when map reading.


I agree with you that when walking on a heading, 5 degrees is about as good as it gets, and that corresponds well with the inherent capabilities of a normal baseplate compass. That's enough for "dead reckoning" navigation but when it comes to establishing a fix (which every so often we must), we tend to rely heavily on terrain association and a good map to get more accuracy. That works well for most of us, most of the time. In more challenging environments, such as woodland or, conversely, feature-poor moors we may have to rely on accurate back-bearings or resection using features quite far away. For those situations, we need a better sighting compass, IMHO. A mirror compass can give us 2 degrees accuracy with care. A prismatic compass is twice as good as that, but you'll have to go to a chandlers to find a good one, these days, at a reasonable price!

The term "variation" was (AFIK) defined long ago, by mariners to mean the difference (E or W) between magnetic north and true north. The term "declination" is never used, at sea, as a synonym for "variation" because it is used instead to describe a completely different kind of angle in astro-navigation. The two norths for mariners are true north and magnetic north. The lines on a marine chart are lines of latitude and longitude. The latter are aligned N-S (true) and the chart projections commonly used (Mercator and Polar) cause lines of longitude always to be straight lines. In the former projection, lines of latitude are also straight lines; in the latter they are concentric circles. Marine charts do not utilise a regular grid and there is therefore no such thing as grid north.

On land, we use gridded maps because we can (there are technical reasons why regular square grids are feasible only for relatively small areas and won't work on oceanic scales) and because they are much more convenient. Consequently, it is grid north which is most useful. As I said in an earlier post, grid north (be it UTM, OS or whatever) cannot be the same as true north, except at one designated meridian. Therefore, the angle between magnetic north and grid north is nearly always different from the "variation" described above. This is why I chose to use the term Grid Magnetic Angle (GMA) in my previous post.

I've looked up "magnetic declination" and in every definition I've seen it is identical to "variation" i.e. it is related to true north, not whatever grid north one might happen to be using. Misuse of these terms is confusing and if this applies to military training (which I hope it doesn't) it's positively dangerous. Imagine what might happen if an SAS soldier were to call in a missile from a ship using a bearing which the soldier and the sailor  interpreted differently!

pauldawes

  • Veteran Member
  • *****
  • Posts: 1391
Re: Practicalities of compass and map navigation
« Reply #31 on: 14:04:30, 27/08/20 »
Apart from proving you can do it...what is point nowadays of navigating with a compass as opposed to a GPS?


What are the advantages?? (Yes..I know ability to interpret a map is necessary...but GPS doesn’t magically stop you understanding a map!)

BuzyG

  • Veteran Member
  • *****
  • Posts: 1938
Re: Practicalities of compass and map navigation
« Reply #32 on: 14:24:24, 27/08/20 »
Apart from proving you can do it...what is point nowadays of navigating with a compass as opposed to a GPS?


What are the advantages?? (Yes..I know ability to interpret a map is necessary...but GPS doesn’t magically stop you understanding a map!)

Light weight.
No power requirements.
No subscriptions.

Plus, for me personally I find using a compass quicker to glance at and follow in low viz on a bearing, than a GPS. So for me, actually better in those limited circumstances too.

Don't get me wrong my standard navigating technique in low Viz these days is... I use GPS for location.  I then set my compass from the GPS map, takes seconds to do. Then I follow the bearing on my compass. O0

There are also those frequent occasions when navigating by eye, where you lose sight of your next way point due to an obstruction, typically walking into the base of a hill or in intermittent cloud.  It's so simple to just set a compass bearing, before the obstruction obscures your view, then follow it until you pick up the sighted way point again.
« Last Edit: 14:31:28, 27/08/20 by BuzyG »

pauldawes

  • Veteran Member
  • *****
  • Posts: 1391
Re: Practicalities of compass and map navigation
« Reply #33 on: 14:56:21, 27/08/20 »
Light weight.
No power requirements.
No subscriptions.

Plus, for me personally I find using a compass quicker to glance at and follow in low viz on a bearing, than a GPS. So for me, actually better in those limited circumstances too.

Don't get me wrong my standard navigating technique in low Viz these days is... I use GPS for location.  I then set my compass from the GPS map, takes seconds to do. Then I follow the bearing on my compass. O0

There are also those frequent occasions when navigating by eye, where you lose sight of your next way point due to an obstruction, typically walking into the base of a hill or in intermittent cloud.  It's so simple to just set a compass bearing, before the obstruction obscures your view, then follow it until you pick up the sighted way point again.


That’s an excellent summary.


And I must admit that I do quite often use a compass when a “fairly rough direction” will do...e.g. if you know if you keep walking on more or less right direction you are going to hit a rail feature, and know which way you want to follow the rail feature once you hit it.


But..for pin point navigation especially in bad visibility...the GPS will be coming out of rucksack before the words “Jack Robinson” can be uttered.

GoneWest

  • Full Member
  • ***
  • Posts: 122
Re: Practicalities of compass and map navigation
« Reply #34 on: 15:02:21, 27/08/20 »
Apart from proving you can do it...what is point nowadays of navigating with a compass as opposed to a GPS?


What are the advantages?? (Yes..I know ability to interpret a map is necessary...but GPS doesn’t magically stop you understanding a map!)


Broadly, I'm with BuzyG on this one. To give you another reason, though, it's possible, now and then, just to want to navigate with a map and compass. Geeky, perhaps, but it can add interest (for me) to a solo walk. As a "born" scientist/engineer, as someone who once sailed a lot and as a onetime member of the Royal Institute of Navigation, I just can't leave stuff like this alone. ::)

ninthace

  • Veteran Member
  • *****
  • Posts: 7236
Re: Practicalities of compass and map navigation
« Reply #35 on: 15:22:11, 27/08/20 »
My GPS has a compass screen and is clipped to my shoulder strap so is instantly accessible.  If I am likely to be out in poor visibility I will have loaded the gps with a route.  This had 2 advantages over the standard compass.  If I need to do the handheld bit, I already know where I am and  I can just walk, keeping the arrow on the line.  If I am pushed off my line by an obstacle such as a bog, I can see how far off line I am and converge gently on my intended route.  My gps can be set to alarm if I stray too far off route.  Provided I am on, or close to, my intended line it stays silent.  If my get more than a predetermined distance off route, it will give a beep to draw my attention so I do not even need to look at it - I can just enjoy the walk and picking my line.  I find that I make much better progress as a result.
Solvitur Ambulando

ninthace

  • Veteran Member
  • *****
  • Posts: 7236
Re: Practicalities of compass and map navigation
« Reply #36 on: 15:24:05, 27/08/20 »
Light weight.
No power requirements.
No subscriptions.

Plus, for me personally I find using a compass quicker to glance at and follow in low viz on a bearing, than a GPS. So for me, actually better in those limited circumstances too.

Don't get me wrong my standard navigating technique in low Viz these days is... I use GPS for location.  I then set my compass from the GPS map, takes seconds to do. Then I follow the bearing on my compass. O0

There are also those frequent occasions when navigating by eye, where you lose sight of your next way point due to an obstruction, typically walking into the base of a hill or in intermittent cloud.  It's so simple to just set a compass bearing, before the obstruction obscures your view, then follow it until you pick up the sighted way point again.
I bet you use a pen and paper or pocket calculator to fill in a spreadsheet too  ;D
Solvitur Ambulando

BuzyG

  • Veteran Member
  • *****
  • Posts: 1938
Re: Practicalities of compass and map navigation
« Reply #37 on: 15:39:30, 27/08/20 »
I bet you use a pen and paper or pocket calculator to fill in a spreadsheet too  ;D


What's a pen.  ;D


As for using a pocket calculator, I have a mk1 Cranium, full of wee cells. that still runs fine on Weetabix. If that can't do the job, I use a computer. ;)

GinAndPlatonic

  • Veteran Member
  • *****
  • Posts: 1002
Re: Practicalities of compass and map navigation
« Reply #38 on: 16:05:17, 27/08/20 »
A compass may be fine for many situations such as highlands , Welsh hills , Dartmoor etc etc , but if you are going to take a walk in many of the Midlands counties like Warwickshire or Worcestershire then you are forever changing direction to go round field edges , estates , farm buildings and the list goes on & on . It is virtually all fenced off one way or another .

So a bearing toward a way point is not an option because in low lying and reasonably flat land , as in these counties you do not get to see one or head toward , that is further away than a few hundred yards any way .
But yesterday at Hay Bluff in Wales with my paper map tile in pocket , and the high winds & some rain , I still relished using my little & very, very practical gps rather than clinging onto my paper map .

Virtue is more to be feared than vice, because it's excesses are not subject to the regulation of conscience - Adam Smith

ninthace

  • Veteran Member
  • *****
  • Posts: 7236
Re: Practicalities of compass and map navigation
« Reply #39 on: 16:30:21, 27/08/20 »
There was that glorious moment when I was in a minesweeper out of Dartmouth learning to fix a ship's position using a bearing compass.  The process was the usual take 3 bearings on known objects, draw 3 lines on a chart and Bingo, we were somewhere in the resulting triangle.  This process was repeated ad nauseam but at one point I made an error and I ended up with an odd looking triangle.  The boss asked what I was going to do, to which the staff reply was take the bearings again and replot. He then asked me what I should tell the captain in the interim.  The book said I should assume I was in the corner of the triangle closest to danger and advise the captain accordingly so I told him to go left at the next set of lights and head for the harbour as I had us in Weymouth High Street!
Solvitur Ambulando

Apache

  • Jr. Member
  • **
  • Posts: 64
Re: Practicalities of compass and map navigation
« Reply #40 on: 17:33:41, 27/08/20 »
Here's my take.


If you are walking then a 1:25000 map with its field boundaries and extra details is invaluable. With experience and walking greater distances being self sufficient (TGO Challenge for example) then 1:50000 will suffice. I take advantage of an OS subscription to plot the route and print it out. The paper sheet is what I use to navigate. Usually it is not necessary to consult a compass. A compass can be useful for orientating the map in the same position as the ground. It is also useful to determine which path to take by comparing the direction on the map with the direction of the path. On featureless moorland crossings a compass is invaluable for transferring a bearing to walk on from map to the ground (usually by sighting a feature on the ground and walking to it, ideally counting steps).
Of course when you get lost a way of position fixing becomes vital. A sextant or more likely nowadays Sat Nav is useful.


I personally find following a track on a Sat Nav very limiting as I then lose the big picture and get tied up with electronics.

April

  • Veteran Member
  • *****
  • Posts: 8291
Re: Practicalities of compass and map navigation
« Reply #41 on: 17:36:37, 27/08/20 »
I'm not sure what others were talking about but the variation I was referring to was between grid north and magnetic north, true north is never considered when map reading.

I was and I assume most other people were too. As a walker I have never once even thought about where true north is in 45 years of using a map and compass.

I have read the rest of the posts with interest. I still prefer to use a map and compass to navigate with GPS as backup if I need to check where we are. I admit to using GPS and Viewranger to navigate when I am feeling lazy  ;) 

@ ninthace, I planned this weekend's 3 day trip to Scotland using a paper OS map and a piece of string with mile markers on it, then counted the contour lines to work out how much ascent. I could have plotted the routes on the viewranger app on the laptop but what fun would there be in doing that?  ;)   ;D



"Who would've thought...... you are light and darkness coming through" words by Tim Armstrong

ninthace

  • Veteran Member
  • *****
  • Posts: 7236
Re: Practicalities of compass and map navigation
« Reply #42 on: 18:16:37, 27/08/20 »
I was and I assume most other people were too. As a walker I have never once even thought about where true north is in 45 years of using a map and compass.

I have read the rest of the posts with interest. I still prefer to use a map and compass to navigate with GPS as backup if I need to check where we are. I admit to using GPS and Viewranger to navigate when I am feeling lazy  ;) 

@ ninthace, I planned this weekend's 3 day trip to Scotland using a paper OS map and a piece of string with mile markers on it, then counted the contour lines to work out how much ascent. I could have plotted the routes on the viewranger app on the laptop but what fun would there be in doing that?  ;)   ;D
How quaint - you will be telling me you have a map case next!  ;D
I like my gps and/or phone because it leaves me free to walk without using a map and get that smug feeling when I sometimes glance at it to find I am exactly where I thought I was!

Solvitur Ambulando

April

  • Veteran Member
  • *****
  • Posts: 8291
Re: Practicalities of compass and map navigation
« Reply #43 on: 18:27:57, 27/08/20 »
[/font]How quaint - you will be telling me you have a map case next!  ;D  
[/font]


No, I don't have a map case  :)


The paper map and tablet are put in beefys stretchy back panel of his rucksack for ease of access if I need to check either.


I end up carrying neither  :D
"Who would've thought...... you are light and darkness coming through" words by Tim Armstrong

sparnel

  • Veteran Member
  • *****
  • Posts: 962
Re: Practicalities of compass and map navigation
« Reply #44 on: 20:37:10, 27/08/20 »
'in 45 years of using a map and compass'   No way April......you're just a slip of a girl!