Newbie Navigation Questions

Blake

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First of probably many, im looking for a bit of a hand on some of the finer aspects of navigation.

I'll be the first to admit ive let my map and compass skills slide a fair bit. As most of my walking and 4wding navigation have been on tracks for a long time I have let my overland skills fall by the wayside which is a bad thing for such a critical skill. However Im rectifying that and getting myself refreshed.

Ive come to a conundrum and was wondering if someone can give me the thumbs up or correct me if im misunderstanding. Ive come across this because I normaly use a Silva baseplate compass but Im learning to use a lensatic compass also. With the lensatic compass Im going to use (Cammenga Lensatic). It has the ruler on the edge and a lubers line with a bezel. So although you dont have the orienting lines you should be able to do everything (and more) you can with the baseplate?

What I was doing in testing was placing the compass lined up with grid north, rotating the map and compass (on a flat surface) untill it points north. (no need for declination calculations) Then line the compass up from location to destination to get my heading. If I was taking bearings from "outside info" based on true north I would have to adjust for declination however is that correct? Is that the correct way to use that style of lensatic compass?

Just want to see if im gon the right track or learning bad habbits doing it that way.

Cheers,
Blake
 
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Corin

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What I was doing in testing was placing the compass lined up with grid north, rotating the map and compass (on a flat surface) untill it points north. (no need for declination calculations) Then line the compass up from location to destination to get my heading. If I was taking bearings from "outside info" based on true north I would have to adjust for declination however is that correct? Is that the correct way to use that style of lensatic compass?
I don't use this type of compass so forgive me if I am also a bit out of my usual field however you comment interests me.

On a standard topographic map which in our area normally has say 12 degrees declination, if you did as you say, the map would be out by 12 degrees in its orientation, when you orientated grid north to magnetic north. when you take your bearing between the two points on the map, you would be out by the same amount, hence would the declination not cancel out. You could not navigate directly off the orientated map with this method but you could set and follow a bearing.

I don't do it this way. It confuses me for some reason. something about intentionally working with errors.
I find it easier to work with bearings on the map in respect to grid north, and convert to magnetic if required. (or visa versa).

Mostly it is grid north and magnetic north that will be used, You rarely need to work with true north for anything. Unless you are into Navigating by the Sun and Stars.
 

chutes

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Blake, it sounds to me like you got the basic gist of it from what I remember.

I used to use an old US Army lensatic compass when I was in Venturers, but I have since lost the art due to those mega-easy Silva baseplate compi. Now I just get confused ;) However, you've inspired me to get hold of another lensatic compass and re-learn the art - I seem to remember using one was complex but they are very accurate.

Here's a Youtube tutorial on using a lensatic compass -

[video=youtube;8a-RvrR_IOo]http://www.youtube.com/watch?v=8a-RvrR_IOo[/video]
[video=youtube;Y9PMLXLQa4Y]http://www.youtube.com/watch?v=Y9PMLXLQa4Y&feature=related[/video]
[video=youtube;3QlhsuwVj5g]http://www.youtube.com/watch?v=3QlhsuwVj5g&feature=related[/video]

And for good measure, a PDF on using the Cammeranga Lensatic Compass from a Pommy perspective (remember they are also used to using a Silva type or a UK military type prismatic compass) - http://www.cunninghameramblers.org.uk/TW - Lensatic Compass Evaluation.pdf

A US Army training PDF for orienting a map using Cammeranga - http://trainingnco.pbworks.com/f/071-329-1011+Orient+a+Map+Using+a+Lensatic+Compass.pdf

And finally, the US Army training handbook on Land Navigation designed for use with the very same compass - http://www.uvm.edu/~goldbar/FM3_25.26.pdf
 

Templar

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With the Lensatic, if you open it up and lay it flat on the map, it's basiclly become a baseplate compass that you can use like your Silva type, just line the two points up with the ruler edge and read your bearing off from the compass card using the non-movable lubbers line.

As for the differences, you still need to do your mag to grid and grid to mag calculations for accurate Nav.
 

Bartnmax

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Just a small word of caution.
The Cammenga is a compass designed for use by the US military & as such it's usually oriented toward navigation in the northern hemisphere.
As I understand it (please feel free to correct me if I'm wrong) the weighting of the compass needle differs between compass' designed for use in northern vs sourthern hemnispheres.
The reason for this is that the Earth's actual magnetic poles are not on the surface of the planet but rather they are inside the Earth. This means that a certain amount of weighting of the needle is required to counteract needle 'dip'. The weighting of the needle differs between nthrn & sthrn hemisphere compasses as the depth of the magnetic poles also differ between Nth & Sth.
This can lead to inaccuracies if using the wrong compass.

Bill A.
 

swampy99

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You can get a southern weighted cammenga http://www.fusiongear.com.au/compasses-cammenga-c-32_68.html
As with all map and compass I refer to my old army way. When going from a grid to a mag bearing I find what the difference is from the map I am using. it may be an old map so you will have to do some calculation of change over the years. But for the northan hemisphere it was GRID TO MAG ADD. MAG TO GRID GET RID. For the southern hehisphere this is reversed (like everything else) MAG TO GRID =ADD. GRID TO MAG =GET RID. With this simple thing you realy cant go wrong.

I now use the silva sighting baseplate compass so you can get a good mag bearing by sighting and then still use it as a good baseplate for the maps.
But would love a cammenga as they seem bomb proof and cost about the same as the silva.

Hope that helps.
 

Corin

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On a standard topographic map which in our area normally has say 12 degrees declination, if you did as you say, the map would be out by 12 degrees in its orientation, when you orientated grid north to magnetic north. when you take your bearing between the two points on the map, you would be out by the same amount, hence would the declination not cancel out. You could not navigate directly off the orientated map with this method but you could set and follow a bearing.
I had a think about this and I am wrong. If you do this way you will be out by the declination, ie signifigantly out on your bearing. for your method to work you would need to orientate the map first. (see my article on the subject)
 

Blake

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Just a small word of caution.
The Cammenga is a compass designed for use by the US military & as such it's usually oriented toward navigation in the northern hemisphere.
As I understand it (please feel free to correct me if I'm wrong) the weighting of the compass needle differs between compass' designed for use in northern vs sourthern hemnispheres.
The reason for this is that the Earth's actual magnetic poles are not on the surface of the planet but rather they are inside the Earth. This means that a certain amount of weighting of the needle is required to counteract needle 'dip'. The weighting of the needle differs between nthrn & sthrn hemisphere compasses as the depth of the magnetic poles also differ between Nth & Sth.
This can lead to inaccuracies if using the wrong compass.

Bill A.
Gday Bill, yep thats correct. However..

In regards to the Cammenga specifically (I cant speak for others) Cammenga Lensatic compasses are designed to function accurately anywhere in the world, although their may be a slight noticeable dip it (allegedly) wont effect the accuracy even in Australia (zone 5). However, Cammenga do supply models balanced specifically for the Southern Hemisphere if you want perfect balance.
 

Blake

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you would need to orientate the map first.
Ah... yes thank you your right. (had to sit and think about it for 10 minutes before I got it. :sorrriso:)

What if alternitavley I had the declination scale available? So if I line up my compass on the declination line, rotate the map and compass untill it points north. Would that be an acceptable way to orient the map? What are the disadvantages to this. Basicly the whole point of this is to try and reduce my need to adding and subtracting declinaton since im terrible with numbers. Although only easy, basic add and subtract im still parinoid off making a mistake therefore trying to reduce the mathematical steps.

I found a video which shows exactly what im trying to do, with the same compass too:

[video=youtube;H4SKU20vVL0]http://www.youtube.com/watch?v=H4SKU20vVL0[/video]
 
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swampy99

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Thats a good example and is great if you are in a class room doing this as you will have a nice hard surface to keep the map on and not move it. Try that on grassy ground or uneven ground and you will have errors. Plus as I stated you need to take in the age of the map. as the mag north may change by example 0.5 degrees a year and say the map is 10 years old it could be out by 5 degrees. If your walking on a bearing over 5ks you could be 500m's off target unless you are using the aim off method.

Just my 2p worth.
 

Dusty Miller

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Yes, the magnetic field is changing, and the rate of change is also getting faster too. A little OT, but I was just reading some geology books and apparently there is a lava flow with one magnetic orientation (NS) at the bottom and a different one at the top (SN). The experts say it would have taken 15 days for tthe lava to cool and solidify, so the entire field flipped in around 15 days. Had no idea it could happen so rapidly. Hope it doesn't happen when away on a longer trip, could be difficult navigating with that sort of thing going on.
 

Walker

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We normally use a traditional baseplate compass (Silva, etc) to work from map to compass, or compass to map (accuracy is important), then use a lensatic compass to hold the bearing to follow (sighting).

So, the baseplate compass is kept secure in a map case with the maps, while the lensatic is only used when trudging through the bush - they are more robust.

We'd never use a lensatic to triangulate our position onto a map unless only a rough estimation is needed.
 

Corin

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Thats a good example and is great if you are in a class room doing this as you will have a nice hard surface to keep the map on and not move it. Try that on grassy ground or uneven ground and you will have errors. Plus as I stated you need to take in the age of the map. as the mag north may change by example 0.5 degrees a year and say the map is 10 years old it could be out by 5 degrees. If your walking on a bearing over 5ks you could be 500m's off target unless you are using the aim off method.

Just my 2p worth.
I totally agree. Though again think I would be lost with this compass. I have never used one.

Note: Even if you are using the aim off method you will be out with a potential for bad results. If you are aiming off 200m on one side of your target on a creek line and the error puts you out 500m you will be either 700m away from your target, or 300m off on the wrong side. Either way it is going to give you a headache.

We teach kids as young as 10 and 11 to calculate declination, I am pretty sure you will manage Blake!
 
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Blake

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righto, ill stick to that. Just thought I would ask the question thats all.
 

Corin

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I sounded a bit blunt in my last post, I did not mean to. It is a valid point you make though Whatever way you do it it must be simple and you must be so implicitly familiar with it that you can do it confidently when you are stressed and under pressure. Times when you will get confused even if you don't think you are. Like anything the key is practice practice practice!
 

Blake

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No not at all mate, I didn't take it that way at all. This is the problem with forums. :) I'll be sure to practice and practice some more. Thanks for the help guys
 

Stewart Townsend

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I don't know if this will help.

I call it magnetic variation. It should have a diagram on the map. It will say how much easterly of westerly variation when the map is made and will also the annual change. You have to make that calculation to be accurate.
I thought there was both easterly and westerly variation on both hemispheres.
The compass is magnetic. A map is grid.
If you calculate a bearing or whatever on the map (grid) you must take the variation into account when using the compass. Sama sama to take a bearing with your compass and want to transfer it to your map you have to take the magnetic variation.
For easterly variation, Magnetic Grid Add and Grid Magnetic Subtract. Just always remember Grand Ma Sucks for easterly.

Hope it might help
 

Walker

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Knowing The System

Here's an article I recently came across:

Altered Grid References

Any bushwalker who uses grid references probably knows that the system used in Australia was changed a few years ago. It has actually been changed a few times, and the whole business is quite complicated, but most of these complications do not affect us because we normally only work to the nearest 100 metres and we do not use very old maps. In fact we only have to worry about the systems which were adopted in 1966, 1984 and 1994.

Also, the 1966 and 1984 systems are the same, as far as walkers are concerned, so we only have to know about the ‘old’ system (1966/1984) and the ‘new’ system (1994).

The basic reason for the changes is that the earth is not a perfect sphere. If it was, latitudes and longitudes would be very simple. However the earth is a slightly flattened sphere and has other irregularities, and is represented by a ‘spheroid’ rather than a sphere. Various spheroids (and ‘ellipsoids’ – we are not concerned about the difference here) have been used in different times and places and, when the Government decides to change spheroids, the latitude and longitude of a given point, such as the top of Kosciuszko, change. This changes the grid reference of the point, because grid systems are related to latitude and
longitude.

The recent history of changes in Australia is as follows:

1. Before 1966 different spheroids were used in different parts of Australia and grid references were given in yards. I do not know how such grid references can be converted to the current system, but would any bushwalker want to do so anyway?

2. In 1966 the Government adopted an Australia-wide metric system, known as the Australian Map Grid 1966 (AMG66), based on the Australian Geodetic Datum 1966 (AGD66). It is generally called ‘AGD66’.

3. In 1984 the previous system was refined and became the Australian Map Grid 1984 (AMG84), based on the Australian Geodetic Datum 1984 (AGD84). It is generally called ‘AGD84’.

4. The changes from AGD66 to AGD84 were only a few metres and are not relevant to walkers, so these systems can be regarded as the same system. You will find that AGD66 and AGD84 have been used on your older maps and on some current ones, such as the maps that apply to Kakadu.

5. In 1994 the Government adopted an international system, and used it to create the Map Grid of Australia 1994 (MGA94), based on the Geocentric Datum of Australia 1994 (GDA94). It is generally called ‘GDA94’. It differs from AGD66 and AGD84 by up to about 200 metres and is used on most new maps in Australia, including all new maps in NSW. It is also used in GPS units.

Whenever you give a grid reference you would normally say which map it is on, and you should also say which system it is based on, which will normally be AGD66, AGD84 or GDA94.

Informally, walkers often use ‘old system’ for AGD66 and AGD84 and ‘new system’ or ‘current system’ for GDA94. Sometimes you will have to convert grid references from AGD66 or AGD84 to GDA94. The following method can be used.

Grid references used by walkers look like 123456, where 123 is the ‘easting’ and 456 is the ‘northing’. Add 1 to the easting, to get 124. Add 2 to the northing, to get 458. Join the new northing and easting to get a grid reference of 124458. To convert from GDA94 to AGD66 or AGD84, subtract 1 from the easting and 2 from the northing. Thus 124458 becomes 123456.

The ‘1’ that you used for the easting and the ‘2’ that you used for the northing represent 100 metres and 200 metres respectively. These are good approximations throughout Australia. Anyone who wanted to work to greater accuracy, say the nearest 10 metres, would have to allow for variations within Australia.

One effect of changing the system is that a new map may cover a slightly different area to the equivalent old map. Therefore, if you are using a new map and an old one which are adjacent to each other, they may overlap by up to 200 metres, or there may be a gap between the areas covered. Hopefully, there will not be an important feature in this gap!
 
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